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xr16l2552 -industry smallest package uart with 2.25v to 5.5v operation home news careers investor relations contact us partnernet login search communications interface power management support info request how to order samples how to buy design technical documentation technical faqs product finder product tree technical support packaging evaluation boards cross references product change notifications obsolescence interface brochure ibis models bsdl ici uart finder xr16l2552 print this page industry smallest package uart with 2.25v to 5.5v operation features l wide range supply voltage operation of 2.25v to 5.5v l automatic rts/cts hardware flow control l automatic xon/xoff software flow control l 16-byte transmit/receive fifo to reduce bandwidth requirements of external cpu l wireless infrared encoder and decoder l full modem interface (txd, rxd, rts, cts, dtr,dsr, ri, cd) l pb-free, rohs compliant versions offered applications l handheld appliances l battery operated instruments l portable appliances l cdma cellular phones l cellular base stations l telecommunications network routers l industrial automation controls description this dual-channel product family is highly integrated and built for small board space, low voltage and high bandwidth requirements found in a variety of handheld and battery operated applications. these include point-of-sale (pos) terminals, tablets and notepads, cdma cellular phones, expansion modules, instrumentation, cellular base stations, wireless infrared appliances and industrial automation controls. the series consists of four devices: xr16l2450, xr16l2550, xr16l2551 and xr16l2552. each has two independently controlled uart channels and operates over a broad range power source of 2.25v to 5.5v with 5v tolerant inputs. the xr16l2551 uniquely offers a very small 32-qfn, 5x5x0.9mm, package with powersave feature to conserve power down to less than 30ua* of current consumption. these attributes are a perfect combination for tight space and/or battery operated designs. the specifications ch 2 cpuinterface intel data rate@5/3.3/2.5v 3.1/1.8/1.0 tx/rxfifo(bytes) 16/16 tx/rxfifoctrs no tx/rxfifoint trig no/ 4 levels autorts/cts yes irdasup yes 5vtolinputs yes sup v 2.25-5.5 pkgs plcc-44, tqfp-48 documents datasheets datasheet version 1.1.1 may 2005 748.60 kb schematics pci eval board schematic version 1.1.0 july 2007 167.82 kb isa eval board schematic version 1.4.0 august 2007 109.05 kb evaluation board manuals evaluation board user's manual version 1.3.0 august 2003 24.69 kb http://www.exar.com/common/content/productdetails.aspx?id=xr16l2552 (1 of 2) [31-jul-09 12:10:37 pm]
xr16l2552 -industry smallest package uart with 2.25v to 5.5v operation quality and reliability quality & reliability homepage material declaration sheets quality manual quarterly quality & reliability report rohs-green solutions powersave feature eliminates the need for two external octal transceivers to reduce board space requirement and lower overall system costs. the xr16l2551 also offers a pin select for intel or motorola data bus interface to reduce hardware design cycle. the xr16l2550, xr16l2551 and xr16l2552 have 16-byte of tx and rx fifos for larger data buffering and provide automatic hardware (rts/cts) or software (xon/xoff) flow control to eliminate receiver data overflow and wasteful re-transmissions. in addition, the devices include the wireless infrared encoder/decoder for wireless communications. the xr16l2450 has one byte of tx and rx fifo as its predecessor, the st16c2450, but with lower operating voltage and 5v tolerant inputs. the 4 devices are pin and function compatible with their previous 5v series. for uart technical support or to obtain an ibis model for this product, please email exar's uart technical support group. part number pkg code rohs min temp. (c) max temp. (c) status buy now order samples xr16l2552ij-f plcc44 -40 85 active XR16L2552IM-F tqfp48 -40 85 active part status legend active - the part is released for sale, standard product. eol (end of life) - the part is no longer being manufactured, there may or may not be inventory still in stock. cf (contact factory) - the part is still active but customers should check with the factory for availability. longer lead-times may apply. pre (pre-introduction) - the part has not been introduced or the part number is an early version available for sample only. obs (obsolete) - the part is no longer being manufactured and may not be ordered. nrnd (not recommended for new designs) - the part is not recommended for new designs. ? 2000-2009 exar corporation, fremont california, u.s.a. terms of use | site map http://www.exar.com/common/content/productdetails.aspx?id=xr16l2552 (2 of 2) [31-jul-09 12:10:37 pm]
exar corporation 48720 kato road, fremont ca, 94538 ? (510) 668-7000 ? fax (510) 668-7017 ? www.exar.com xr xr16l2552 2.25v to 5.5v duart with 16-byte fifo may 2005 rev. 1.1.1 general description the xr16l2552 (l2552) is a dual universal asynchronous receiver and transmitter (uart) with 5 volt tolerant inputs. the xr16l2552 is an improved version of the st16c2552 uart with lower operating voltages and 5 volt tolerant inputs. the l2552 provides enhanced uart functions with 16 byte tx and rx fifos, automatic hardware (rts/cts) and software (xon/xoff) flow control, and a complete modem control interface. onboard status registers provide the user with error indications and operational status. indepedendent programmable baud rate generators are provided to select transmit and receive clock rates up to 3.125mbps. an internal loop-back capability allows onboard diagnostics. the l2552 provides block mode data transfers (dma) through fifo controls. dma transfer monitoring is provided through the signals txrdy# and rxrdy#. an alternate function register provides the user with the ability to write the contro l registers for both uarts concurrently and selection of the multi-function output (baudout#, op2#, or rxrdy#). n ote : 1 covered by u.s. patent #5,649,122. applications ? portable appliances ? telecommunication network routers ? ethernet network routers ? cellular data devices ? factory automation and process controls features ? 2.25 to 5.5 volt operation ? 5 volt tolerant inputs ? pin-to-pin and functionally compatible to national pc16552 ? pin-to-pin compatible to exar?s st16c2552, xr16l2752 and xr16c2852 in the 44-plcc ? 2 independent uart channels up to 3.125mbps with external clock of 50 mhz register set compatible to 16c550 16 byte transmit fifo to reduce the bandwidth requirement of the external cpu 16 byte receive fifo with error tags to reduce the bandwidth requirement of the external cpu 4 selectable rx fifo trigger levels automatic rts/cts hardware flow control automatic xonxoff soft ware flow control wireless infrared encoder/decoder full modem interface (cts#, rts#, dsr#, dtr#, ri#, cd#) programmable character lengths (5, 6, 7, 8) with even, odd, or no parity multi-function output allows more package functions with fewer i/o pins ? concurrent write to channels a and b ? crystal oscillator or external clock input ? 48-tqfp (7x7x1.0 mm) and 44-plcc packages f igure 1. xr16l2552 b lock d iagram mfa# (op2a#, baudouta#, or rxrdya#) mfb# (op2b#, baudoutb#, or rxrdyb#) xtal1 xtal2 crystal osc/buffer txa 8-bit data bus interface uart channel a 16 byte tx fifo 16 byte rx fifo brg tx & rx uart regs 2.25 to 5.5 volt vcc gnd 2552blk uart channel b (same as channel a) a2:a0 d7:d0 cs# chsel inta intb iow# ior# reset txrdy# a/b rxrdy# a/b (48-tqfp only) cts#a/b, ri#a/b, cd#a/b, dsr#a/b rxa modem control logic dtr#a/b, rts#a/b txb rxb * 5 volt tolerant inputs
xr16l2552 xr 2.25v to 5.5v duart with 16-byte fifo rev. 1.1.1 2 f igure 2. p in o ut a ssignments ordering information p art n umber p ackage o perating t emperature r ange d evice s tatus xr16l2552im 48-lead tqfp -40c to +85c active xr16l2552ij 44-lead plcc -40c to +85c active 6 5 4 3 2 1 44 43 42 41 40 7 8 9 10 11 12 13 14 15 16 17 39 38 37 36 35 34 33 32 31 30 29 18 19 20 21 22 23 24 25 26 27 28 d5 d6 d7 a0 xtal1 gnd xtal2 a1 a2 chsel intb rxa txa dtra# rtsa# mfa# inta vcc txrdyb# rib# cdb# dsrb# cs# mfb# iow# reset gnd rtsb# ior# rxb txb dtrb# ctsb# d4 d3 d2 d1 d0 txrdya# vcc ria# cda# dsra# ctsa# xr16l2552 44-pin plcc 48 47 46 45 44 43 42 41 40 39 38 37 1 2 3 4 5 6 7 8 9 10 11 12 36 35 34 33 32 31 30 29 28 27 26 25 13 14 15 16 17 18 19 20 21 22 23 24 d5 d6 d7 a0 xtal1 gnd xtal2 a1 a2 chsel intb cs# mfb# iow# reset gnd rtsb# nc ior# rxb txb dtrb# ctsb# rxa txa dtra# rtsa# mfa# rxrdya# inta vcc txrdyb# rib# cdb# dsrb# d4 d3 d2 d1 d0 txrdya# vcc ria# cda# dsra# ctsa# nc xr16l2552 48-pin tqfp rxrdyb# 48-tqfp package 44-plcc package
xr xr16l2552 rev. 1.1.1 2.25v to 5.5v duart with 16-byte fifo 3 pin descriptions pin description n ame 48-tqfp p in # 44-plcc p in # t ype d escription data bus interface a2 a1 a0 10 9 4 15 14 10 i address data lines [2:0]. these 3 address lines select one of the internal reg - isters in uart channel a/b during a data bus transaction. d7 d6 d5 d4 d3 d2 d1 d0 3 2 1 48 47 46 45 44 9 8 7 6 5 4 3 2 i/o data bus lines [7:0] (bidirectional). ior# 20 24 i input/output read strobe (active low). the falling edge instigates an internal read cycle and retrieves the data byte from an internal register pointed to by the address lines [a2:a0]. the data byte is placed on the data bus to allow the host processor to read it on the rising edge. iow# 15 20 i input/output write strobe (active low). the falling edge instigates an internal write cycle and the rising edge transfers the data byte on the data bus to an internal register pointed by the address lines. cs# 13 18 i uart chip select (active low). this function selects channel a or b in accor - dance with the logical state of the chsel pin. this allows data to be trans - ferred between the user cpu and the l2552. chsel 11 16 i channel select - uart channel a or b is selected by the logical state of this pin when the cs# pin is a logic 0. a logic 0 on the chsel selects the uart channel b while a logic 1 selects uart channel a. normally, chsel could just be an address line from the user cpu such as a3. bit-0 of the alternate function register (afr) can temporarily override chsel function, allowing the user to write to both channel regist er simultaneously with one write cycle when cs# is low. it is especially useful during the in itialization routine. inta 30 34 o uart channel a interrupt output (active high). a logic high indicates channel a is requesting for service. intb 12 17 o uart channel b interrupt output (active high). a logic high indicates channel b is requesting for service. txrdya# 43 1 o uart channel a transmitter ready (act ive low). the output provides the tx fifo/thr status for transmit channel a. if it is not used, leave it uncon - nected. rxrdya# 31 - o uart channel a receiver ready (active low). this output provides the rx fifo/rhr status for receive channel a. this pin is only available on the 48- pin tqfp package. if it is not used, leave it unconnected. txrdyb# 28 32 o uart channel b transmitter ready (active low). the output provides the tx fifo/thr status for transmit channel b. if it is not used, leave it uncon - nected.
xr16l2552 xr 2.25v to 5.5v duart with 16-byte fifo rev. 1.1.1 4 rxrdyb# 8 - o uart channel b receiver ready (active low). this output provides the rx fifo/rhr status for receive channel b. th is pin is only available on the 48- pin tqfp package. if it is not used, leave it unconnected. modem or serial i/o interface txa 35 38 o uart channel a transmit data. if it is not used, leave it unconnected. rxa 36 39 i uart channel a receive data. normal receive data input must idle at logic 1 condition. if it is not used, tie it to vc c or pull it high via a 100k ohm resistor. rtsa# 33 36 o uart channel a request-to-send (activ e low) or general purpose output. this output must be asserted prior to using auto rts flow control, see efr[6], mcr[1] and ier[6]. if it is not used, leave it unconnected. ctsa# 38 40 i uart channel a clear-to-send (active lo w) or general purpose input. it can be used for auto cts flow control, see efr[7] and ier[7]. this input should be connected to vcc when not used. dtra# 34 37 o uart channel a data-terminal-ready (active low) or general purpose output. if it is not used, leave it unconnected. dsra# 39 41 i uart channel a data-set-ready (active low) or general purpose input. this input should be connected to vcc when not used. this input has no effect on the uart. cda# 40 42 i uart channel a carrier-detect (active low) or general purpose input. this input should be connected to vcc when not used. this input has no effect on the uart. ria# 41 43 i uart channel a ring-indicator (active low) or general purpose input. this input should be connected to vcc when not used. this input has no effect on the uart. txb 22 26 o uart channel b transmit data. if it is not used, leave it unconnected. rxb 21 25 i uart channel b receive data. normal receive data input must idle at logic 1 condition. if it is not used , tie it to vcc or pull it high via a 100k ohm resistor. rtsb# 18 23 o uart channel b request-to-send (activ e low) or general purpose output. this output must be asserted prior to using auto rts flow control, see efr[6], mcr[1] and ier[6]. if it is not used, leave it unconnected. ctsb# 24 28 i uart channel b clear-to-send (active low) or general purpose input. it can be used for auto cts flow control, see efr[7] and ier[7]. this input should be connected to vcc when not used. dtrb# 23 27 o uart channel b data-terminal-ready (active low) or general purpose output. if it is not used, leave it unconnected. dsrb# 25 29 i uart channel b data-set-ready (active low) or general purpose input. this input should be connected to vcc when not used. this input has no effect on the uart. cdb# 26 30 i uart channel b carrier-detect (active low) or general purpose input. this input should be connected to vcc when not used. this input has no effect on the uart. pin description n ame 48-tqfp p in # 44-plcc p in # t ype d escription
xr xr16l2552 rev. 1.1.1 2.25v to 5.5v duart with 16-byte fifo 5 rib# 27 31 i uart channel b ring-indicator (active low) or general purpose input. this input should be connected to vcc when not used. this input has no effect on the uart. mfa# 32 35 o multi-function output channel a. this output pin can function as the op2a#, baudouta#, or rxrdya# pin. one of these output signal functions can be selected by the user programmable bits 1-2 of the alternate function register (afr). these signal functions are described as follows: 1) op2a# - when op2a# (active low) is selected, the mf# pin is a logic 0 when mcr bit-3 is set to a logic 1 (see mcr bit-3). mcr bit-3 defaults to a logic 1 condition after a reset or power-up. 2) baudouta# - when baudouta# function is selected, the 16x baud rate clock output is available at this pin. 3) rxrdya# - rxrdya# (active low) is intended for monitoring dma data transfers. if using the 48-tqfp package, this output is already available at pin 31. if it is not used, leave it unconnected. mfb# 14 19 o multi-function output channelb. this output pin can function as the op2b#, baudoutb#, or rxrdyb# pin. one of t hese output signal functions can be selected by the user programmable bits 1-2 of the alternate function register (afr). these signal functions are described as follows: 1) op2b# - when op2b# (active low) is selected, the mf# pin is a logic 0 when mcr bit-3 is set to a logic 1 (see mcr bit-3). mcr bit-3 defaults to a logic 1 condition after a reset or power-up. 2) baudoutb# - when baudoutb# functi on is selected, the 16x baud rate clock output is available at this pin. 3) rxrdyb# - rxrdyb# (active low) is intended for monitoring dma data transfers. if using the 48-tqfp package, this output is already available at pin 8. if it is not used, leave it unconnected. ancillary signals xtal1 5 11 i crystal or external clock input. xtal2 7 13 o crystal or buffered clock output. reset 16 21 i reset (active high) - a longer than 40 ns logic 1 pulse on this pin will reset the internal registers and all outputs. the uart transmitter output will be held at logic 1, the receiver input will be ignored and outputs are reset during reset period (see external reset conditions). vcc 29, 42 44, 33 pwr 2.25v to 5.5v power supply. all input pins are 5v tolerant. gnd 6, 17 22, 12 pwr power supply common, ground. pin description n ame 48-tqfp p in # 44-plcc p in # t ype d escription
xr16l2552 xr 2.25v to 5.5v duart with 16-byte fifo rev. 1.1.1 6 pin type: i=input, o=output, i/o= input/output, od=output open drain. 1.0 product description the xr16l2552 (l2552) provides serial asynchronous receive data synchronization, parallel-to-serial and serial-to-parallel data conversions for both the tran smitter and receiver sections. these functions are necessary for converting the serial data stream into para llel data that is required with digital data systems. synchronization for the serial data stream is accomplished by adding start and stop bits to the transmit data to form a data character (character orientated protocol). da ta integrity is ensured by at taching a parity bit to the data character. the parity bit is checked by the receiv er for any transmission bit errors. the electronic circuitry to provide all these functions is fair ly complex especially when manufactur ed on a single in tegrated silicon chip. the l2552 represents such an integration with gr eatly enhanced features. the l2552 is fabricated with an advanced cmos process. transmit and receive fifos (16 bytes each) the l2552 is an upward solution th at provides a dual uart capability wi th 16 bytes of tran smit and receive fifo memory, instead of none in the 16c2450. the l2 552 is designed to work with low voltage supplies and high performance data communication systems, that requir e fast data processing time. increased performance is realized in the l2552 by the transmit and receive fifo ?s. this allows the external processor to handle more networking tasks within a given ti me. for example, the st16c2450 wit hout a receive fifo, will require unloading of the rhr in 93 microseconds (this example us es a character length of 11 bits, including start/stop bits at 115.2 kbps). this means the external cpu will have to service the receive fifo less than every 100 microseconds. however with the 16 byte fifo in the l2552, the data buffer will no t require unloading/loading for 1.53 ms. this increases the service interval giving the external cpu additional ti me for other applications and reducing the overall uart interrupt servicing time. in addition, the 4 selectable receive fifo trigger interrupt levels is uniquely provided for maximum data throughput performance especially when operating in a multi-channel environment. the fifo memory greatly reduces the bandwidth requirement of the external controlling cpu, increase s performance, and redu ces power consumption. enhanced features the xr16l2552 integrates the func tions of 2 enhanced 16c550 universal asynchronous receiver and transmitter (uart). each uart is independently cont rolled having its own set of device configuration registers. the configuration registers set is 16550 ua rt compatible for control, status and data transfer. additionally, each uart channel has automatic rts/cts hardware flow control, automatic xon/xoff and special character software flow control, infrared enco der and decoder (irda ver 1.0), programmable baud rate generator with a prescaler of divide by 1 or 4, and data rate up to 4 mbps at 5v. data rate the l2552 is capable of operation up to 3.125 mbps with a 50 mhz external clock. with a crystal or external clock input of 14.7456 mhz the user can select data rates up to 921.6 kbps. the rich feature set of the l2552 is available through in ternal registers. selectable receive fifo trigger levels, selectable tx and rx baud rates, and modem interface controls are all standard features. following a power on reset or an external reset, the l2552 is software compatible with the 16l2752 and 16c2852. nc 19, 37 - - not connected internally. pin description n ame 48-tqfp p in # 44-plcc p in # t ype d escription
xr xr16l2552 rev. 1.1.1 2.25v to 5.5v duart with 16-byte fifo 7 2.0 functional descriptions 2.1 cpu interface the cpu interface is 8 data bits wide with 3 address li nes and control signals to execute data bus read and write transactions. the l2552 data interface supports the intel compatible types of cp us and it is compatible to the industry standard 16c550 uart. no clock (oscillato r nor external clock) is required to operate a data bus transaction. each bus cycle is asynchronous usi ng cs#, ior# and iow# signals. both uart channels share the same data bus for host operations. the data bus interconnections are shown in figure 3 . . 2.2 5-volt tolerant inputs the l2552 can accept up to 5v inputs even when oper ating at 3.3v or 2.5v. but note that if the l2552 is operating at 2.5v, its v oh may not be high enough to meet the requirements of the v ih of a cpu or a serial transceiver that is operating at 5v. 2.3 device reset the reset input resets the internal registers and the seri al interface outputs in both channels to their default state (see the ta b l e 13 ). an active high pulse of longer than 40 ns duration will be required to activate the reset function in the device. 2.4 device identification and revision the l2552 provides a device identification code and a devi ce revision code to distinguish the part from other devices and revisions. to read the identification code from the part, it is required to set the baud rate generator registers dll and dlm both to 0x00. now reading the content of th e dlm will provide 0x02 to indicate l2552 and reading the content of dll will pr ovide the revision of the part; for example, a reading of 0x01 means revision a. f igure 3. xr16l2552 d ata b us i nterconnections vcc vcc (op2a#) dsra# ctsa# rtsa# dtra# rxa txa ria# cda# (op2b#) dsrb# ctsb# rtsb# dtrb# rxb txb rib# cdb# gnd a0 a1 a2 uart_cs# uart_chsel ior# iow# d0 d1 d2 d3 d4 d5 d6 d7 a0 a1 a2 cs# chsel d0 d1 d2 d3 d4 d5 d6 d7 ior# iow# uart channel a uart channel b uart_intb uart_inta intb inta (rxrdya#) txrdya# (rxrdya#) txrdya# (rxrdyb#) txrdyb# (rxrdyb#) txrdyb# uart_reset reset rs-232 serial interface rs-232 serial interface (baudoutb#) (baudouta#) pins in parentheses become available through the mf# pin. mf# a/b becomes rxrdy# a/b when afr[2:1] = '10'. mf# a/b becomes op2 # a/b when afr[2:1] = '00'. mf# a/b becomes baudout# a/b when afr[1:0] = '01'. rxrdy# pins available on 48-tqfp package.
xr16l2552 xr 2.25v to 5.5v duart with 16-byte fifo rev. 1.1.1 8 2.5 channel a and b selection the uart provides the user with the capability to bi-directionally tr ansfer information be tween an external cpu and an external serial communication device. a logic 0 on chip select pin (cs#) allows the user to select the uart and then using the channel select (chsel) pin, the user can select channel a or b to configure, send transmit data and/or unload receive data to/from th e uart. individual channel select functions are shown in ta b l e 1 . 2.6 channel a and b internal registers each uart channel in the l2552 has a set of enhanced registers for controlling, m onitoring and data loading and unloading. the configuration register set is compat ible to those already available in the standard single 16c550 and dual st16c2550. these r egisters function as data holding regi sters (thr/rhr), interrupt status and control registers (isr/ier), a fi fo control register (fcr), receive lin e status and control registers (lsr/ lcr), modem status and control regist ers (msr/mcr), programmable data rate (clock) divisor registers (dll/ dlm), and a user accessible scratchpad register (spr). beyond the general 16c2550 features and capabilities, the l2552 offers enhance d feature registers (afr, efr, xon/xoff 1, xon/xoff 2) that provide automatic rts and cts hardware flow control, automatic xon/xoff software flow control, and simultaneous writes to both channels. all the register functions are discussed in full detail later in ?section 3.0, uart internal registers? on page 21 . 2.7 simultaneous write to channel a and b during a write mode cycle, the setting of alternate function register (afr ) bit-0 to a logic 1 will override the chsel selection and allows a simultan eous write to both uart channel se ctions. this functional capability allow the registers in both uart channels to be modified concurrently, saving indivi dual channel initialization time. caution should be exer cised, however, when using this capability. any in-process se rial data transfer may be disrupted by changing an active channel?s mode. 2.8 dma mode the device does not support direct memory access. th e dma mode (a legacy term) in this document doesn?t mean ?direct memory access? but refers to data block transfer operation. the dma mode affects the state of the rxrdy# a/b (mf# a/b becomes rxrdy# a/b output when afr[2:1] = ?10?) and txrdy# a/b output pins. the transmit and receive fifo trigger levels provide additional fl exibility to the user for block mode operation. the lsr bits 5-6 provide an indication when the transmitter is empty or has an empty location(s) for more data. the user can optionally operate the transmit and receive fifo in the dma mode (fcr bit-3=1). when the transmit and receive fifo are enabled and the dma mode is disabled (fcr bit-3 = 0), the l2552 is placed in single-character mode for data transmit or receive operation. when dma mode is enabled (fcr bit- 3 = 1), the user takes advantage of block mode opera tion by loading or unloading the fifo in a block sequence determined by the programmed trigger level. the following table show their behavior. also see figure 18 through figure 23 . t able 1: c hannel a and b s elect cs# chsel f unction 1 x uart de-selected 0 1 channel a selected 0 0 channel b selected
xr xr16l2552 rev. 1.1.1 2.25v to 5.5v duart with 16-byte fifo 9 2.9 inta and intb ouputs the inta and intb interrupt outputs change according to the operating mode and enahnced features setup. ta b l e 3 and ta b l e 4 summarize the operating behavior for the transmitter and receiver. also see figure 18 through figure 23 . 2.10 crystal oscillator or external clock input the l2552 includes an on-chip oscillator (xtal1 and xtal2) to produce a clock for both uart sections in the device. the cpu data bus does not r equire this clock for bus operation. the crystal oscillator provides a system clock to the baud rate generators (brg) section found in each of the uart. xtal1 is the input to the oscillator or external clock buffer input with xtal 2 pin being the output. fo r programming details, see ?programmable baud rate generator.? t able 2: txrdy# and rxrdy# o utputs in fifo and dma m ode p ins fcr bit -0=0 (fifo d isabled ) fcr b it -0=1 (fifo e nabled ) fcr bit-3 = 0 (dma mode disabled) fcr bit-3 = 1 (dma mode enabled) rxrdy# a/b 0 = 1 byte. 1 = no data. 0 = at least 1 byte in fifo 1 = fifo empty. 1 to 0 transition when fifo reaches the trigger level, or timeout occurs. 0 to 1 transition when fifo empties. txrdy# a/b 0 = thr empty. 1 = byte in thr. 0 = fifo empty. 1 = at least 1 byte in fifo. 0 = fifo has at least 1 empty location. 1 = fifo is full. t able 3: inta and intb p ins o peration for t ransmitter fcr b it -0 = 0 (fifo d isabled ) fcr b it -0 = 1 (fifo e nabled ) inta/b pin 0 = a byte in thr 1 = thr empty 0 = at least 1 byte in fifo 1 = fifo empty t able 4: inta and intb p in o peration f or r eceiver fcr b it -0 = 0 (fifo d isabled ) fcr b it -0 = 1 (fifo e nabled ) inta/b pin 0 = no data 1 = 1 byte 0 = fifo below trigger level 1 = fifo above trigger level
xr16l2552 xr 2.25v to 5.5v duart with 16-byte fifo rev. 1.1.1 10 the on-chip oscillator is designed to use an industry standard micropro cessor crystal (p arallel resonant, fundamental frequency with 10-22 pf capacitance load, esr of 20-120 ohms and 100ppm frequency tolerance) connected externally betw een the xtal1 and xtal2 pins (see figure 2 ), with an external 500k ? to 1 m ? resistor across it. alternatively, an external clock can be connected to the xtal1 pin to clock the internal baud rate generato r for standard or custom rates. typica l oscillator connections are shown in figure 4 . for further reading on oscillator circuit please se e application note dan 108 on exar?s web site. 2.11 programmable baud rate generator a single baud rate generator is provided for the trans mitter and receiver, allowing independent tx/rx channel control. the programmable baud rate generator is capa ble of operating with a crystal frequency of up to 24 mhz. however, with an external clock input on xtal 1 pin and a 2k ohms pull-up resistor on xtal2 pin (as shown in figure 5 ) it can extend its operation up to 64 mhz (4mbps serial data rate) at room temperature and 5.0v. f igure 4. t ypical oscillator connections f igure 5. e xternal c lock c onnection for e xtended d ata r ate c1 22-47 pf c2 22-47 pf y1 1.8432 mhz to 24 mhz r1 0-120 ? (optional) r2 500 k ? ? 1 m ? xtal1 xtal2 2k xtal1 xtal2 r1 vcc external clock vcc gnd
xr xr16l2552 rev. 1.1.1 2.25v to 5.5v duart with 16-byte fifo 11 to obtain maximum data rate, it is necessary to use full rail swing on the clock input. see external clock operating frequency over power supply voltage chart in figure 6 . the l2552 divides the basic external clock by 16. the basic 16x clock provides table rates to support standard and custom applications using the sa me system design. the baud rate ge nerator divides this 16x clock by any divisor from 1 to 2 16 -1. the rate table is configured via th e dll and dlm internal register functions. customized baud rates can be achieved by selecting th e proper divisor values for the msb and lsb sections of baud rate generator. ta b l e 5 shows the standard data rates available with a 14.7456 mhz crystal or external clock at 16x sampling rate. when using a non-standard frequency crystal or ex ternal clock, the divisor value can be calculated for dll/dlm with the following equation. f igure 6. o perating f requency c hart . r equires a 2k ohms pull - up resis - tor on xtal2 pin to increase operating speed divisor (decimal) = (xtal1 or external clock frequency ) / (serial data rate x 16) t able 5: t ypical data rates with a 14.7456 mh z crystal or external clock o utput data rate mcr bit-7=0 d ivisor for 16x clock (decimal) d ivisor for 16x clock (hex) dlm p rogram v alue (hex) dll p rogram v alue (hex) d ata r ate e rror (%) 400 2304 900 09 00 0 2400 384 180 01 80 0 4800 192 c0 00 c0 0 9600 96 60 00 60 0 19.2k 48 30 00 30 0 38.4k 24 18 00 18 0 76.8k 12 0c 00 0c 0 60 50 40 30 3.0 4.5 5.5 3.5 4.0 5.0 suppy voltage xtal1 external clock frequency in mhz. 70 80 85 o c 25 o c -40 o c operating frequency for xr16l2552 with external clock and a 2k ohms pull-up resistor on xtal2 pin.
xr16l2552 xr 2.25v to 5.5v duart with 16-byte fifo rev. 1.1.1 12 2.12 transmitter the transmitter section comprises of an 8-bit transmit shift register (tsr) and 16 bytes of fifo which includes a byte-wide transmit holding register (thr). tsr shifts out every data bit with the 16x internal clock. a bit time is 16 clock perio ds. the transmitter sends the start-bit followed by the number of data bits, inserts the proper parity-bit if enabled, and adds the stop -bit(s). the status of the fi fo and tsr are reported in the line status register (lsr bit-5 and bit-6). 2.12.1 transmit holding re gister (thr) - write only the transmit holding register is an 8-bit register pr oviding a data interface to the host processor. the host writes transmit data byte to the thr to be converted in to a serial data stream including start-bit, data bits, parity-bit and stop-bit(s). the least-si gnificant-bit (bit-0) becomes first data bit to go out. the thr is the input register to the transmit fifo of 16 bytes when fifo operation is enabl ed by fcr bit-0. every time a write operation is made to the thr, the fifo data pointer is automatically bumped to the next sequential data location. 2.12.2 transmitter operation in non-fifo mode the host loads transmit data to thr one character at a time. the thr empty flag (lsr bit-5) is set when the data byte is transferred to tsr. thr flag can generate a tr ansmit empty interrupt (isr bit-1) when it is enabled by ier bit-1. the tsr flag (lsr bit-6) is set when tsr beco mes completely empty. 2.12.3 transmitter operation in fifo mode the host may fill the transmit fifo with up to 16 bytes of transmit data. t he thr empty flag (lsr bit-5) is set whenever the fifo is empty. the thr empty flag can ge nerate a transmit empty interrupt (isr bit-1) when the transmit empty interrupt is enabled by ier bit-1. the tsr flag (lsr bit-6) is set when the fifo and the tsr become empty. 153.6k 6 06 00 06 0 230.4k 4 04 00 04 0 460.8k 2 02 00 02 0 921.6k 1 01 00 01 0 f igure 7. t ransmitter o peration in non -fifo m ode t able 5: t ypical data rates with a 14.7456 mh z crystal or external clock o utput data rate mcr bit-7=0 d ivisor for 16x clock (decimal) d ivisor for 16x clock (hex) dlm p rogram v alue (hex) dll p rogram v alue (hex) d ata r ate e rror (%) transmit holding register (thr) transmit shift register (tsr) data byte l s b m s b thr interrupt (isr bit-1) enabled by ier bit-1 txnofifo1 16x clock
xr xr16l2552 rev. 1.1.1 2.25v to 5.5v duart with 16-byte fifo 13 2.13 receiver the receiver section contains an 8-bit receive shift register (rsr) and 16 bytes of fifo which includes a byte-wide receive holding regi ster (rhr). the rsr uses the 16x for ti ming. it verifies and validates every bit on the incoming character in the middle of each data bit. on the falling edge of a start or false start bit, an internal receiver counter star ts counting at the 16x. after 8 clocks the start bit period should be at the center of the start bit. at this time the start bit is sampled and if it is still a logic 0 it is validated. evaluati ng the start bit in this manner prevents the receiver from assembling a false ch aracter. the rest of the data bits and stop bits are sampled and validated in this same manner to prevent false framing. if there were any error(s), they are reported in the lsr register bits 2-4. upon unloading the receive data byte from rhr, the receive fifo pointer is bumped and the error tags are immediately updated to reflect the status of the data byte in rhr register. rhr can generate a receive data ready interrupt upon receiv ing a character or delay until it reaches the fifo trigger level. furthermore, data delivery to the host is guaranteed by a receive data ready time-out interrupt when data is not received for 4 word lengths as defined by lcr[1:0] plus 12 bits ti me. this is equivalent to 3.7- 4.6 character times. the rhr interrupt is enabled by ier bit-0. 2.13.1 receive holding register (rhr) - read-only the receive holding register is an 8-bit register that holds a receive data byte from the receive shift register. it provides the receive data interface to the host processor. the rhr register is part of the receive fifo of 16 bytes by 11-bits wide, the 3 extra bits are fo r the 3 error tags to be reported in lsr register. when the fifo is enabled by fcr bit-0, the rhr contains th e first data character received by the fifo. after the rhr is read, the next character byte is loaded into the rhr and the errors associated with the current data byte are immediately updated in the lsr bits 2-4 f igure 8. t ransmitter o peration in fifo and f low c ontrol m ode transmit data shift register (tsr) transmit data byte thr interrupt (isr bit-1) falls below the programmed trigger level and then when becomes empty. fifo is enabled by fcr bit-0=1 transmit fifo 16x clock auto cts flow control (cts# pin) auto software flow control flow control characters (xoff1/2 and xon1/2 reg. txfifo1
xr16l2552 xr 2.25v to 5.5v duart with 16-byte fifo rev. 1.1.1 14 . f igure 9. r eceiver o peration in non -fifo m ode f igure 10. r eceiver o peration in fifo and a uto rts f low c ontrol m ode receive data shift register (rsr) receive data byte and errors rhr interrupt (isr bit-2) receive data holding register (rhr) rxfifo1 16x clock receive data characters data bit validation error tags in lsr bits 4:2 receive data shift register (rsr) rxfifo1 16x clock error tags (16-sets) error tags in lsr bits 4:2 16 bytes by 11-bit wide fifo receive data characters fifo trigger=8 example : - rx fifo trigger level selected at 8 bytes data fills to 14 data falls to 4 data bit validation receive data fifo receive data receive data byte and errors rhr interrupt (isr bit-2) programmed for desired fifo trigger level. fifo is enabled by fcr bit-0=1 rts# de-asserts when data fills above the flow control trigger level to suspend remote transmitter. enable by efr bit-6=1, mcr bit-2. rts# re-asserts when data falls below the flow control trigger level to restart remote transmitter. enable by efr bit-6=1, mcr bit-2.
xr xr16l2552 rev. 1.1.1 2.25v to 5.5v duart with 16-byte fifo 15 2.14 auto rts (hardware) flow control automatic rts hardware flow control is used to prevent data overrun to the local receiver fifo. the rts# output is used to request remote unit to suspend/r esume data transmission. the auto rts flow control features is enabled to fit specific application requirement (see figure 11 ): ? enable auto rts flow control using efr bit-6. ? the auto rts function must be started by asserting rts# output pin (mcr bit-1 to logic 1 after it is enabled). if using the auto rts interrupt: ? enable rts interrupt through ier bit-6 (after setting efr bit-4). the uart issues an interrupt when the rts# pin makes a transition from low to high: isr bit-5 will be set to logic 1. 2.15 auto cts flow control automatic cts flow control is used to prevent data overrun to the remote receiver fifo. the cts# input is monitored to suspend/restart the local transmitter. the aut o cts flow control feature is selected to fit specific application requirement (see figure 11 ): ? enable auto cts flow control using efr bit-7. if using the auto cts interrupt: enable cts interrupt through ier bit-7 (after setting efr bit-4). the uart issues an interrupt when the cts# pin is de-asserted (high): isr bit-5 will be set to 1, and uart will suspend transmission as soon as the stop bit of the character in process is shifted out. transm ission is resumed after the cts# input is re-asserted (low), indicating more data may be sent.
xr16l2552 xr 2.25v to 5.5v duart with 16-byte fifo rev. 1.1.1 16 f igure 11. a uto rts and cts f low c ontrol o peration the local uart (uarta) starts data transfer by asserting rtsa# (1). rtsa# is normally connected to ctsb# (2) of remote uart (uartb). ctsb# allows its transmitter to se nd data (3). txb data arrives and fills uarta receive fifo (4). when rxa data fills up to its receive fifo trigger le vel, uarta activates its rxa data ready interrupt (5) and con - tinues to receive and put data into it s fifo. if interrupt service latency is l ong and data is not being unloaded, uarta monitors its receive data fill level to match the upper th reshold of rts delay and de-assert rtsa# (6). ctsb# follows (7) and request uartb transmitter to suspend data transfer. ua rtb stops or finishes sending the data bits in its trans - mit shift register (8). when receive fifo data in uarta is unloaded to match the lower threshold of rts delay (9), uarta re-asserts rtsa# (10), ctsb# recognizes the change (11) and restarts its transmitter and data flow again until next receive fifo trigger (12). this same event applies to the reverse direction when uarta sends data to uartb with rtsb# and ctsa# controlling the data flow. rtsa# ctsb# rxa txb transmitter receiver fifo trigger reached auto rts trigger level auto cts monitor rtsa# txb rxa fifo ctsb# remote uart uartb local uart uarta on off on suspend restart rts high threshold data starts on off on assert rts# to begin transmission 1 2 3 4 5 6 7 receive data rts low threshold 9 10 11 receiver fifo trigger reached auto rts trigger level transmitter auto cts monitor rtsb# ctsa# rxb txa inta (rxa fifo interrupt) rx fifo trigger level rx fifo trigger level 8 12 rtscts1
xr xr16l2552 rev. 1.1.1 2.25v to 5.5v duart with 16-byte fifo 17 2.16 auto xon/xoff (software) flow control when software flow control is enabled ( see table 12 ), the l2552 compares one or two sequential receive data characters with the programmed xon or xoff-1,2 character value(s). if receive character(s) (rx) match the programmed values, th e l2552 will halt transmission (tx) as soon as the current character has completed transmission. when a match occurs, the xoff (if enabled vi a ier bit-5) flag will be set and the interrupt output pin will be activated. following a susp ension due to a match of the xoff character, the l 2552 will monitor the receive data stream for a ma tch to the xon-1,2 character. if a match is found, the l2552 w ill resume operation and clear the flags (isr bit-4). reset initially sets the contents of the xon/xoff 8-bit flow control registers to a logic 0. following reset the user can write any xon/xoff value desired for software flow c ontrol. different conditions can be set to detect xon/ xoff characters ( see table 12 ) and suspend/resume transmissions. when double 8-bit xon/xoff characters are selected, the l2552 compares two consecutive receive c haracters with two software flow control 8-bit values (xon1, xon2, xoff1, xoff2) and controls tx transmissi ons accordingly. under the above described flow control mechanisms, flow control characters are not placed (sta cked) in the user accessible rx data buffer or fifo. in the event that the receive buffer is overfilling and fl ow control needs to be exec uted, the l2552 automatically sends an xoff message (when enabled) via the serial tx output to the remote modem. the l2552 sends the xoff-1,2 characters two-character-times (= time taken to send two characters at the programmed baud rate) after the receive fifo crosses the prog rammed trigger level. to clear this condition, th e l2552 will transmit the programmed xon-1,2 characters as soon as receive fifo is less than one trigger level below the programmed trigger level. see table 6 below. * after the trigger level is reached, an xoff character is se nt after a short span of time (= time required to send 2 characters); for example, after 2.083ms has elapsed for 9600 b aud and 8-bit word length, no parity and 1 stop bit setting. 2.17 special character detect a special character detect feature is provided to detect an 8-bit character when bit-5 is set in the enhanced feature register (efr). when this character (xoff2) is detected, it will be placed in the fi fo along with normal incoming rx data. the l2552 compares each incoming receive characte r with xoff-2 data. if a matc h exists, the received data will be transferred to fifo and isr bit-4 will be set to indica te detection of special character. although the internal register table shows xon, xoff registers with eight bits of character information, the actual number of bits is dependent on the programmed word lengt h. line control register (lcr) bits 0-1 defines the number of character bits, i.e., either 5 bits, 6 bits, 7 bits, or 8 bits. the word length selected by lcr bits 0-1 also determines the number of bits that will be used for the special character comparison. bit-0 in the xon, xoff registers corresponds with the lsb bit for the receive character. t able 6: a uto x on /x off (s oftware ) f low c ontrol rx t rigger l evel int p in a ctivation x off c haracter ( s ) s ent ( characters in rx fifo ) x on c haracter ( s ) s ent ( characters in rx fifo ) 1 1 1* 0 4 4 4* 1 8 8 8* 4 14 14 14* 8
xr16l2552 xr 2.25v to 5.5v duart with 16-byte fifo rev. 1.1.1 18 2.18 infrared mode the l2552 uart includes the infrared encoder and decoder compatible to the irda (infrared data association) version 1.0. the irda 1.0 standard th at stipulates the infrared encoder sends out a 3/16 of a bit wide high-pulse for each ?0? bit in the transmit data st ream. this signal encoding reduces the on-time of the infrared led, hence reduces the power consumption. see figure 12 below. the infrared encoder and decoder are enabled by setting m cr register bit-6 to a ?1?. when the infrared feature is enabled, the transmit data output, tx, idles at logic zero level. likewise, the rx input assumes an idle level of logic zero from a reset and power up, see figure 12 . typically, the wireless infrared decoder receives the input pulse from the infrared sensing diode on the rx pin. each time it senses a light pulse, it re turns a logic 1 to the data bit stream. f igure 12. i nfrared t ransmit d ata e ncoding and r eceive d ata d ecoding character data bits start stop 0000 0 11 111 bit time 1/16 clock delay irdecoder - rx data receive ir pulse (rx pin) character data bits start stop 0000 0 11 111 tx data transmit ir pulse (tx pin) bit time 1/2 bit time 3/16 bit time irencoder-1
xr xr16l2552 rev. 1.1.1 2.25v to 5.5v duart with 16-byte fifo 19 2.19 sleep mode with auto wake-up the l2552 supports low voltage system designs, hence, a sleep mode is included to reduce its power consumption when the chip is not actively used. all of these conditions must be satisf ied for the l2552 to enter sleep mode: no interrupts pending for both channels of the l2552 (isr bit-0 = 1) divisor is a non-zero value (ie. dll = 0x1) sleep mode of both channels are enabled (ier bit-4 = 1) modem inputs are not toggling (msr bits 0-3 = 0) rx input pins are idling at a logic 1 the l2552 stops its crystal oscillator to conserve power in the sleep mode . user can check the xtal2 pin for no clock output as an indication that the device has entered the sleep mode. the l2552 resumes normal operation by any of the following: a receive data start bit transition (logic 1 to 0) a data byte is loaded to the transmitter, thr or fifo a change of logic state on any of the modem or general purpose serial inputs: cts#, dsr#, cd#, ri# if the l2552 is awakened by any one of the above conditions, it will return to the sleep mode aut omatically after all interrupting conditions have been serviced and clear ed. if the l2552 is awakened by the modem inputs, a read to the msr is required to re set the modem inputs. in any case, t he sleep mode will not be entered while an interrupt is pending from channel a or b. the l2552 will stay in the sleep mode of o peration until it is disabled by setting ier bit-4 to a logic 0. if the address lines, data bus lines, iow#, ior#, csa#, csb#, and modem input lines remain steady when the l2552 is in sleep mode, th e maximum current will be in the microamp range as specified in the dc electrical characteristics on page 36 . if the input lines are floating or are toggling while the l2552 is in sleep mode, the current can be up to 100 times more. if any of those signals are toggling or floating, then an external buffer would be required to keep the address, data and control lines steady to achieve the low current. as an alternative, please refer to the xr16l2551 with the powersave feature that eliminates any unnecessary external buffer. a word of caution: owing to the star ting up delay of the crystal oscillato r after waking up from sleep mode, the first few receive characters may be lost. the number of ch aracters lost during the restart also depends on your operating data rate. more characters are lost when operati ng at higher data rate. also, it is important to keep rx a/b inputs idling at logic 1 or ?m arking? condition during sleep mode to avoid receiving a ?break? condition upon the restart. this may occur when the external inte rface transceivers (rs-232, rs-485 or another type) are also put to sleep mode and cannot maintain the ?mar king? condition. to avoid this, the designer can use a 47k-100k ohm pull-up resistor on the rxa and rxb pins.
xr16l2552 xr 2.25v to 5.5v duart with 16-byte fifo rev. 1.1.1 20 2.20 internal loopback the l2552 uart provides an intern al loopback capability for system diagnostic purposes. the internal loopback mode is enabled by setting mcr register bit-4 to logi c 1. all regular uart functions operate normally. figure 13 shows how the modem port signals are re-configured. transmit data from the transmit shift register output is internally routed to the receive shift register input allowing the system to re ceive the same data that it was sending. the tx pin is held at logic 1 or mark condition while rts# and dtr# are de-asserted, and cts#, dsr# cd# and ri# inputs are ig nored. caution: the rx input must be held to a logic 1 during loopback test else upon exiting the loopback test the uart may de tect and report a false ?break? signal. also, auto rts/ cts is not supported during internal loopback. f igure 13. i nternal l oop b ack in c hannel a and b txa/txb rxa/rxb modem / general purpose control logic internal data bus lines and control signals rtsa#/rtsb# mcr bit-4=1 vcc vcc transmit shift register (thr/fifo) receive shift register (rhr/fifo) ctsa#/ctsb# dtra#/dtrb# dsra#/dsrb# ria#/rib# cda#/cdb# op1# op2# rts# cts# dtr# dsr# ri# cd# vcc vcc (op2a#/op2b#)
xr xr16l2552 rev. 1.1.1 2.25v to 5.5v duart with 16-byte fifo 21 3.0 uart internal registers each of the uart channel in the l2552 has its own set of configuration registers selected by address lines a0, a1 and a2 with cs# and chsel selecting the channel. the registers are 16c550 compatible. the complete register set is shown in ta b l e 7 and ta b l e 8 . t able 7: uart channel a and b uart internal registers a2,a1,a0 a ddresses r egister r ead /w rite c omments 16c550 c ompatible r egisters 0 0 0 rhr - receive holding register thr - transmit holding register read-only write-only lcr[7] = 0 0 0 0 dll - div latch low byte read/write lcr[7] = 1, lcr 0xbf 0 0 1 dlm - div latch high byte read/write 0 1 0 afr - alternate function register read/write 0 0 0 drev - device revision read/write lcr[7] = 1, lcr 0xbf, dll = 0x00, dlm = 0x00 0 0 1 dvid - device id read/write 0 0 1 ier - interrupt enable register read/write lcr[7] = 0 0 1 0 isr - interrupt status register fcr - fifo control register read-only write-only 0 1 1 lcr - line control register read/write 1 0 0 mcr - modem control register read/write lcr 0xbf 1 0 1 lsr - line status register reserved read-only write-only 1 1 0 msr - modem status register reserved read-only write-only 1 1 1 spr - scratch pad register read/write e nhanced r egisters 0 1 0 efr - enhanced function register read/write lcr = 0xbf 1 0 0 xon-1 - xon character 1 read/write 1 0 1 xon-2 - xon character 2 read/write 1 1 0 xoff-1 - xoff character 1 read/write 1 1 1 xoff-2 - xoff character 2 read/write
xr16l2552 xr 2.25v to 5.5v duart with 16-byte fifo rev. 1.1.1 22 . t able 8: internal registers description. s haded bits are enabled when efr b it -4=1 a ddress a2-a0 r eg n ame r ead / w rite b it -7 b it -6 b it -5 b it -4 b it -3 b it -2 b it -1 b it -0 c omment 16c550 compatible registers 0 0 0 rhr rd bit-7 bit-6 bit-5 bit-4 bit-3 bit-2 bit-1 bit-0 lcr[7] = 0 0 0 0 thr wr bit-7 bit-6 bit-5 bit-4 bit-3 bit-2 bit-1 bit-0 0 0 1 ier rd/wr 0/ 0/ 0/ 0/ modem stat. int. enable rx line stat. int. enable tx empty int enable rx data int. enable cts int. enable rts int. enable xoff int. enable sleep mode enable 0 1 0 isr rd fifos enabled fifos enabled 0/ 0/ int source bit-3 int source bit-2 int source bit-1 int source bit-0 int source bit-5 int source bit-4 0 1 0 fcr wr rx fifo trigger rx fifo trigger 0 0 dma mode enable tx fifo reset rx fifo reset fifos enable 0 1 1 lcr rd/wr divisor enable set tx break set par - ity even parity parity enable stop bits word length bit-1 word length bit-0 1 0 0 mcr rd/wr 0/ 0/ 0/ internal lopback enable op2# output control rsvd (op1#) rts# output control dtr# output control lcr 0xbf brg pres - caler ir mode enable xonany 1 0 1 lsr rd rx fifo global error thr & tsr empty thr empty rx break rx fram - ing error rx parity error rx over - run error rx data ready 1 1 0 msr rd cd# input ri# input dsr# input cts# input delta cd# delta ri# delta dsr# delta cts# 1 1 1 spr rd/wr bit-7 bit-6 bit-5 bit-4 bit-3 bit-2 bit-1 bit-0 baud rate generator divisor 0 0 0 dll rd/wr bit-7 bit-6 bit-5 bit-4 bit-3 bit-2 bit-1 bit-0 lcr[7] = 1 lcr 0xbf 0 0 1 dlm rd/wr bit-7 bit-6 bit-5 bit-4 bit-3 bit-2 bit-1 bit-0 0 1 0 afr rd/wr rsvd rsvd rsvd rsvd rsvd rxrdy# select baudout# select concur - rent write 0 0 0 drev rd bit-7 bit-6 bit-5 bit-4 bit-3 bit-2 bit-1 bit-0 lcr[7]=1 lcr 0xbf dll=0x00 dlm=0x00 0 0 1 dvid rd 0 0 0 0 0 0 1 0
xr xr16l2552 rev. 1.1.1 2.25v to 5.5v duart with 16-byte fifo 23 4.0 internal register descriptions 4.1 receive holding register (rhr) - read- only see ?receiver? on page 13. 4.2 transmit holding regi ster (thr) - write-only see ?transmitter? on page 12. 4.3 baud rate generator divisors (dll and dlm) - read/write the baud rate generator (brg) is a 16-bit counter that generates the data rate for the transmitter. the rate is programmed through registers dll and dlm which are on ly accessible when lcr bit-7 is set to ?1?. see ?programmable baud rate generator? on page 10. for more details. 4.4 interrupt enable register (ier) - read/write the interrupt enable register (ier) masks the interrupts from receive data ready, transmit empty, line status and modem status registers. these interrupts are r eported in the interrupt status register (isr). 4.4.1 ier versus receive fifo interrupt mode operation when the receive fifo (fcr bit-0 = 1) and receive interr upts (ier bit-0 = 1) are enabled, the rhr interrupts (see isr bits 2 and 3) status will reflect the following: a. the receive data available interrupts are issued to the host when the fifo has reached the programmed trigger level. it will be cleared when the fifo drops below the programmed trigger level. b. fifo level will be reflected in the isr register when the fifo trigger level is reached. both the isr register status bit and the interrupt will be cleared wh en the fifo drops below the trigger level. c. the receive data ready bit (lsr bit-0) is set as soon as a character is transferred from the shift register to the receive fifo. it is rese t when the fifo is empty. enhanced registers 0 1 0 efr rd/wr auto cts enable auto rts enable special char select enable ier [7:4], isr [5:4], fcr[5:4], mcr[7:5] soft - ware flow cntl bit-3 soft - ware flow cntl bit-2 soft - ware flow cntl bit-1 soft - ware flow cntl bit-0 lcr=0 x bf 1 0 0 xon1 rd/wr bit-7 bit-6 bit-5 bit-4 bit-3 bit-2 bit-1 bit-0 1 0 1 xon2 rd/wr bit-7 bit-6 bit-5 bit-4 bit-3 bit-2 bit-1 bit-0 1 1 0 xoff1 rd/wr bit-7 bit-6 bit-5 bit-4 bit-3 bit-2 bit-1 bit-0 1 1 1 xoff2 rd/wr bit-7 bit-6 bit-5 bit-4 bit-3 bit-2 bit-1 bit-0 t able 8: internal registers description. s haded bits are enabled when efr b it -4=1 a ddress a2-a0 r eg n ame r ead / w rite b it -7 b it -6 b it -5 b it -4 b it -3 b it -2 b it -1 b it -0 c omment
xr16l2552 xr 2.25v to 5.5v duart with 16-byte fifo rev. 1.1.1 24 4.4.2 ier versus receive/transmit fifo polled mode operation when fcr bit-0 equals a logic 1 for fifo enable; rese tting ier bits 0-3 enables the xr16l2552 in the fifo polled mode of operation. since the receiver and transmitter have separate bits in the lsr either or both can be used in the polled mode by selecting respective transmit or receive control bit(s). a. lsr bit-0 indicates there is data in rhr or rx fifo. b. lsr bit-1 indicates an overrun error has occurred and that data in the fifo may not be valid. c. lsr bit 2-4 provides the type of receive data erro rs encountered for the data byte in rhr, if any. d. lsr bit-5 indicates tran smit fifo is empty. e. lsr bit-6 indicates when both the transmit fifo and tsr are empty. f. lsr bit-7 indicates a data error in at least one character in the rx fifo. ier[0]: rhr interrupt enable the receive data ready interrupt will be issued when rhr has a data character in th e non-fifo mode or when the receive fifo has reached the programmed trigger level in the fifo mode. ? logic 0 = disable the receive data ready interrupt (default). ? logic 1 = enable the receiver data ready interrupt. ier[1]: thr interrupt enable this bit enables the transmit re ady interrupt which is issued whenever the tx fifo becomes empty. ? logic 0 = disable transmit ready interrupt (default). ? logic 1 = enable transmit ready interrupt. ier[2]: receive line status interrupt enable if any of the lsr register bits 1, 2, 3 or 4 is a logic 1, it will generate an interrupt to inform the host controller about the error status of the current data byte in fifo. lsr bit-1 generates an interrupt immediately when the character has been received. lsr bits 2-4 generate an in terrupt when the character with errors is read out of the fifo. ? logic 0 = disable the receiver line status interrupt (default). ? logic 1 = enable the receiver line status interrupt. ier[3]: modem status interrupt enable ? logic 0 = disable the modem status register interrupt (default). ? logic 1 = enable the modem status register interrupt. ier[4]: sleep mode enable (requires efr bit-4 = 1) ? logic 0 = disable sleep mode (default). ? logic 1 = enable sleep mode. see sleep mode section for further details. ier[5]: xoff interrupt enable (requires efr bit-4=1) ? logic 0 = disable the software flow cont rol, receive xoff interrupt. (default) ? logic 1 = enable the software flow control, receive xo ff interrupt. see software flow control section for details. ier[6]: rts# output interrupt enable (requires efr bit-4=1) ? logic 0 = disable the rts# interrupt (default). ? logic 1 = enable the rts# interrupt. the uart issues an interrupt when the rts# pin makes a transition from low to high.
xr xr16l2552 rev. 1.1.1 2.25v to 5.5v duart with 16-byte fifo 25 ier[7]: cts# input interrupt enable (requires efr bit-4=1) ? logic 0 = disable the cts# interrupt (default). ? logic 1 = enable the cts# interrupt. the uart issues an interrupt when cts# pin makes a transition from low to high. 4.5 interrupt status register (isr) - read-only the uart provides multiple levels of prioritized interrupts to minimize external software interaction. the interrupt status register (isr) provides the user with six interrupt status bits. performing a read cycle on the isr will give the user the current hi ghest pending interrupt level to be se rviced, others are queued up to be serviced next. no other interrupts are acknowledged until the pending interrupt is serviced. the interrupt source table, ta b l e 9 , shows the data values (bit 0-5) for the interr upt priority levels and the interrupt sources associated with each of these interrupt levels. 4.5.1 interrupt generation: ? lsr is by any of the lsr bits 1, 2, 3 and 4. ? rxrdy is by rx trigger level. ? rxrdy time-out is by a 4-char plus 12 bits delay timer. ? txrdy is by tx fifo empty. ? msr is by any of the msr bits 0, 1, 2 and 3. ? receive xoff/special character is by det ection of a xoff or special character. ? cts# is when its transmitter toggles the input pin (from low to high) during auto cts flow control enabled by efr bit-7. ? rts# is when its receiver toggles th e output pin (from low to high) during auto rts flow control enabled by efr bit-6. 4.5.2 interrupt clearing: ? lsr interrupt is cleared by a read to the lsr register (b ut flags and tags not cleared until character(s) that generated the interrupt(s) has been emptied or cleared from fifo). ? rxrdy interrupt is cleared by reading data until fifo fa lls below the trigger level. ? rxrdy time-out interrupt is cleared by reading rhr. ? txrdy interrupt is cleared by a read to the isr register or writing to thr. ? msr interrupt is cleared by a read to the msr register. ? xoff interrupt is cleared by a read to isr or when xon character(s) is received. ? special character interrupt is cleared by a read to isr or after the next character is received. ? rts# and cts# flow control interrupts are cleared by a read to the msr register.
xr16l2552 xr 2.25v to 5.5v duart with 16-byte fifo rev. 1.1.1 26 ] isr[0]: interrupt status ? logic 0 = an interrupt is pending and the isr contents may be used as a pointer to the appropriate interrupt service routine. ? logic 1 = no interrupt pending (default condition). isr[3:1]: interrupt status these bits indicate the source for a pending interrupt at interrupt priority levels (see interrupt source ta b l e 9 ). isr[4]: xoff or special character interrupt status this bit is enabled when efr bit-4 is set to a logic 1. is r bit-4 indicates that the receiver detected a data match of the xoff character(s). if this is an xoff interrupt, it can be cleared by a read to the isr or when an xon character is received. if it is a spec ial character interrupt, it will automatically clear af ter the next character is received. isr[5]: rts#/cts# interrupt status this bit is enabled when efr bit-4 is set to a logic 1. isr bit-5 indicates that the cts# or rts# has changed state from low to high. isr[7:6]: fifo enable status these bits are set to a logic 0 when the fifos are disa bled. they are set to a logic 1 when the fifos are enabled. 4.6 fifo control register (fcr) - write-only this register is used to enable the fifos, clear the fi fos, set the transmit/receive fifo trigger levels, and select the dma mode. the dma, and fifo modes are defined as follows: fcr[0]: tx and rx fifo enable ? logic 0 = disable the transmit and receive fifo (default). ? logic 1 = enable the transmit and receive fifos. this bit must be set to logic 1 when other fcr bits are written or they will not be programmed. fcr[1]: rx fifo reset this bit is only active when fcr bit-0 is a ?1?. ? logic 0 = no receive fifo reset (default) ? logic 1 = reset the receive fifo pointers and fifo le vel counter logic (the rece ive shift register is not cleared or altered). this bit will return to a logic 0 after resetting the fifo. t able 9: i nterrupt s ource and p riority l evel p riority isr r egister s tatus b its s ource of interrupt l evel b it -5 b it -4 b it -3 b it -2 b it -1 b it -0 1 0 0 0 1 1 0 lsr (receiver line status register) 2 0 0 1 1 0 0 rxrdy (receive data time-out) 3 0 0 0 1 0 0 rxrdy (received data ready) 4 0 0 0 0 1 0 txrdy (transmit ready) 5 0 0 0 0 0 0 msr (modem status register) 6 0 1 0 0 0 0 rxrdy (received xoff or special character) 7 1 0 0 0 0 0 cts#, rts# change of state - 0 0 0 0 0 1 none (default)
xr xr16l2552 rev. 1.1.1 2.25v to 5.5v duart with 16-byte fifo 27 fcr[2]: tx fifo reset this bit is only active when fcr bit-0 is a ?1?. ? logic 0 = no transmit fifo reset (default). ? logic 1 = reset the transmit fifo pointers and fifo le vel counter logic (the transmit shift register is not cleared or altered). this bit will return to a logic 0 after resetting the fifo. fcr[3]: dma mode select controls the behavior of the txrdy# and rxrdy# pins. see dma operation section for details. ? logic 0 = normal operation (default). ? logic 1 = dma mode. fcr[5:4]: reserved fcr[7:6]: receive fifo trigger select (logic 0 = default, rx trigger level =1) these 2 bits are used to se t the trigger level for the receive fifo. th e uart will issue a rece ive interrupt when the number of the characters in the fifo crosses the trigger level. table 10 shows the complete selections. 4.7 line control register (lcr) - read/write the line control register is used to specify the asynchronous data communication format. the word or character length, the number of stop bits, and the parity are selected by writing the appropriate bits in this register. lcr[1:0]: tx and rx word length select these two bits specify the word length to be transmitted or received. lcr[2]: tx and rx stop-bit length select the length of stop bit is specified by this bi t in conjunction with the programmed word length. t able 10: r eceive fifo t rigger l evel s election fcr b it -7 fcr b it -6 r eceive t rigger l evel c ompatibility 0 0 1 1 0 1 0 1 1 (default) 4 8 14 table-a. 16c550, 16c2550, 16c2552, 16c554, 16c580 com - patible. bit-1 bit-0 w ord length 0 0 5 (default) 0 1 6 1 0 7 1 1 8 bit-2 w ord length s top bit length (b it time ( s )) 0 5,6,7,8 1 (default) 1 5 1-1/2 1 6,7,8 2
xr16l2552 xr 2.25v to 5.5v duart with 16-byte fifo rev. 1.1.1 28 lcr[3]: tx and rx parity select parity or no parity can be selected via this bit. the pa rity bit is a simple way used in communications for data integrity check. see ta b l e 11 for parity selection summary below. ? logic 0 = no parity. ? logic 1 = a parity bit is generated during the transmissi on while the receiver checks for parity error of the data character received. lcr[4]: tx and rx parity select if the parity bit is enabled with lcr bit-3 set to a logi c 1, lcr bit-4 selects the even or odd parity format. ? logic 0 = odd parity is generated by forcing an odd number of logic 1?s in the transmitted character. the receiver must be programmed to check the same format (default). ? logic 1 = even parity is gen erated by forcing an even numb er of logic 1?s in the tr ansmitted character. the receiver must be programmed to check the same format. lcr[5]: tx and rx parity select if the parity bit is enabled, lcr bit- 5 selects the forced parity format. ? lcr[5] = logic 0, parity is not forced (default). ? lcr[5] = logic 1 and lcr[4] = logic 0, parity bit is forced to a logical 1 for the transmit and receive data. ? lcr[5] = logic 1 and lcr[4] = logic 1, parity bit is forced to a logical 0 for the transmit and receive data. lcr[6]: transmit break enable when enabled, the break control bit causes a break cond ition to be transmitted (the tx output is forced to a ?space?, logic 0, state). this co ndition remains, until disabled by setting lcr bit-6 to a logic 0. ? logic 0 = no tx break condition (default). ? logic 1 = forces the transmitter output (tx) to a ?space ?, logic 0, for alerting the remote receiver of a line break condition. lcr[7]: baud rate divisors enable baud rate generator divisor (dll/dlm) enable. ? logic 0 = data registers are selected (default). ? logic 1 = divisor latch registers are selected. 4.8 modem control register (mcr) or general purpose outputs control - read/write the mcr register is used for contro lling the serial/modem interface signal s or general pur pose inputs/outputs. t able 11: p arity selection lcr b it -5 lcr b it -4 lcr b it -3 p arity selection x x 0 no parity 0 0 1 odd parity 0 1 1 even parity 1 0 1 force parity to mark, ?1? 1 1 1 forced parity to space, ?0?
xr xr16l2552 rev. 1.1.1 2.25v to 5.5v duart with 16-byte fifo 29 mcr[0]: dtr# output the dtr# pin is a modem control outpu t. if the modem interface is not us ed, this output may be used as a general purpose output. ? logic 0 = force dtr# output to a logic 1 (default). ? logic 1 = force dtr# output to a logic 0. mcr[1]: rts# output the rts# pin is a modem control output. if the modem in terface is not used, this output may be used as a general purpose output. ? logic 0 = force rts# output to a logic 1 (default). ? logic 1 = force rts# output to a logic 0. mcr[2]: op1# output op1# is not available as an output pin on the l2552. but it is available for use during internal loopback mode. in the loopback mode, this bit is used to write the state of the modem ri# interface signal. mcr[3]: op2# output op2# is available as an output pin on the l2552 when af r[2:1] = ?00?. in the loopba ck mode, mcr[3] is used to write the state of the modem cd# interface si gnal. also see pin descriptions for mf# pins. ? logic 0 = forces op2# output to a logic 1 (default). ? logic 1 = forces op2# output to a logic 0. mcr[4]: internal loopback enable ? logic 0 = disable loopback mode (default). ? logic 1 = enable local loopback mode, see loopback section and figure 13 . mcr[5]: xon-any enable ? logic 0 = disable xon-any function (for 16c550 compat ibility, default). ? logic 1 = enable xon-any function. in this mode, any rx character rece ived will resume transmit operation. the rx character will be loaded into the rx fifo , unless the rx character is an xon or xoff character and the l2552 is programmed to use the xon/xoff flow control. mcr[6]: infrared encoder/decoder enable ? logic 0 = enable the standard modem receive an d transmit input/output interface. (default) ? logic 1 = enable infrared irda receive and transmit inputs/outputs. the tx/rx output/input are routed to the infrared encoder/decoder. the data input and output levels conform to the irda infrared interface requirement. while in this mode, the infrared tx ou tput will be a logic 0 during idle data conditions. mcr[7]: clock prescaler select ? logic 0 = divide by one. the input clock from the crystal or external clock is fed directly to the programmable baud rate generator without further modification, i.e., divide by one (default). ? logic 1 = divide by four. the prescaler divides the input clock from the crystal or external clock by four and feeds it to the programmable baud rate generator, hence, data rates become one forth. 4.9 line status register (lsr) - read only this register provides the status of data transfers between the uart and the host. lsr[0]: receive data ready indicator ? logic 0 = no data in receive holding register or fifo (default). ? logic 1 = data has been received and is save d in the receive holding register or fifo.
xr16l2552 xr 2.25v to 5.5v duart with 16-byte fifo rev. 1.1.1 30 lsr[1]: receiver overrun flag ? logic 0 = no overrun error (default). ? logic 1 = overrun error. a data overrun error condition occurred in the receive shift register. this happens when additional data arrives while the fi fo is full. in this case the previous data in the receive shift register is overwritten. note that under this condition the data byte in the receive shift register is not transferred into the fifo, therefore the data in the fifo is not corrupted by the error. lsr[2]: receive data parity error tag ? logic 0 = no parity error (default). ? logic 1 = parity error. the receive character in rhr does not have correct pa rity information and is suspect. this error is associated with the char acter available for reading in rhr. lsr[3]: receive data framing error tag ? logic 0 = no framing error (default). ? logic 1 = framing error. the receive character did not hav e a valid stop bit(s). this error is associated with the character available for reading in rhr. lsr[4]: receive break tag ? logic 0 = no break condition (default). ? logic 1 = the receiver received a break signal (rx was a logic 0 for at least one character frame time). in the fifo mode, only one break character is loaded into the fifo. the break indication remains until the rx input returns to the idle condition, ?mark? or logic 1. lsr[5]: transmit holding register empty flag this bit is the transmit holding regi ster empty indicator. this bit indica tes that the transmitter is ready to accept a new character for transmission. in addition, this bit causes the uart to issue an interrupt to the host when the thr inte rrupt enable is set. the thr bit is set to a logic 1 when the last data byte is transferred from the transmit holding register to the transmit shift regist er. the bit is reset to logic 0 concurrently with the data loading to the transmit holding register by the host. in th e fifo mode this bit is set when the transmit fifo is empty, it is cleared when the transmi t fifo contains at least 1 byte. lsr[6]: thr and tsr empty flag this bit is set to a logic 1 whenever the transmitter goes idle. it is set to logic 0 whenever either the thr or tsr contains a data character. in the fifo mode this bi t is set to a logic 1 whenever the transmit fifo and transmit shift register are both empty. lsr[7]: receive fifo data error flag ? logic 0 = no fifo error (default). ? logic 1 = a global indicator for the sum of all error bits in the rx fifo. at least one parity error, framing error or break indication is in the fifo data. this bit clears when there is no more error(s) in the fifo. 4.10 modem status register (msr) - read only this register provides the current state of the modem interface signals, or othe r peripheral device that the uart is connected. lower four bits of this register are used to indicate the changed information. these bits are set to a logic 1 whenever a signal from the modem changes state. these bits may be used as general purpose inputs/outputs when they are not used with modem signals. msr[0]: delta cts# input flag ? logic 0 = no change on cts# input (default). ? logic 1 = the cts# input has changed state since the la st time it was monitored. a modem status interrupt will be generated if msr interrup t is enabled (ier bit-3).
xr xr16l2552 rev. 1.1.1 2.25v to 5.5v duart with 16-byte fifo 31 msr[1]: delta dsr# input flag ? logic 0 = no change on dsr# input (default). ? logic 1 = the dsr# input has changed state since the last time it was monitored. a modem status interrupt will be generated if msr interrup t is enabled (ier bit-3). msr[2]: delta ri# input flag ? logic 0 = no change on ri# input (default). ? logic 1 = the ri# input has changed from a logic 0 to a logic 1, ending of the ringi ng signal. a modem status interrupt will be ge nerated if msr in terrupt is enabled (ier bit-3). msr[3]: delta cd# input flag ? logic 0 = no change on cd# input (default). ? logic 1 = indicates that the cd# input has changed st ate since the last time it was monitored. a modem status interrupt will be generated if msr interrupt is enabled (ier bit-3). msr[4]: cts input status normally this bit is the co mpliment of the cts# input. however in the loopback mode, this bit is equivalent to the rts# bit in the mcr register. the cts# input may be used as a general purpose input when the modem interface is not used. msr[5]: dsr input status normally this bit is the compliment of the dsr# input. in the loopback mode, this bit is equivalent to the dtr# bit in the mcr register. the dsr# input may be used as a general purpose input when the modem interface is not used. msr[6]: ri input status normally this bit is the compliment of the ri# input. in the loopback mode this bit is equivalent to bit-2 in the mcr register. the ri# input may be used as a general purpose input when the modem interface is not used. msr[7]: cd input status normally this bit is the compliment of the cd# input. in the loopback mode this bit is equivalent to bit-3 in the mcr register. the cd# input may be used as a general purpose input when the modem interface is not used. 4.11 scratch pad register (spr) - read/write this is a 8-bit general purpose register for the user to store temporary data. the content of this register is preserved during sleep mode but becomes 0xff (default) after a reset or a power off-on cycle. 4.12 baud rate generator registers (dll and dlm) - read/write the concatenation of the contents of dlm and dll gives the 16-bit divisor value which is used to calculate the baud rate: ? baud rate = (clock frequency / 16) / divisor see mcr bit-7 and the baud rate table also. 4.13 alternate function register (afr) - read/write this register is used to select spec ific modes of mf# operation and to allow both uart register sets to be written concurrently.
xr16l2552 xr 2.25v to 5.5v duart with 16-byte fifo rev. 1.1.1 32 afr[0]: concurrent write mode when this bit is set, the cpu can wr ite concurrently to the same register in both uarts. this function is intended to reduce the dual uart initialization time . it can be used by the cpu when both channels are initialized to the same state. the external cpu can set or clear this bit by accessing either register set. when this bit is set, the channe l select pin still selects the channel to be accessed during read operations. the user should ensure that lcr bit-7 of both channels are in t he same state before executing a concurrent write to the registers at address 0, 1, or 2. ? logic 0 = no concurrent write (default). ? logic 1 = register set a and b are written concurrently with a single external cpu i/o write operation. afr[2:1]: mf# output select these bits select a signal function for output on the mf# a/b pins. these signal function are described as: op2#, baudout#, or rxrdy#. only one sign al function can be selected at a time. afr[7:3]: reserved all are initialized to logic 0. 4.14 device identification register (dvid) - read only this register contains the device id (0x02 for xr16l25 52). prior to reading this register, dll and dlm should be set to 0x00. 4.15 device revision register (drev) - read only this register contains the device revision information. for example, 0x01 means revision a. prior to reading this register, dll and dlm should be set to 0x00. 4.16 enhanced feature register (efr) enhanced features are enabled or disabled using this register. bit 0-3 provide si ngle or dual consecutive character software flow control selection (see ta b l e 12 ). when the xon1 and xon2 and xoff1 and xoff2 modes are selected, the double 8-bit words are concatenated in to two sequential characters. caution: note that whenever changing the tx or rx flow control bits, always reset all bits back to logic 0 (disable) before programming a new setting. b it -2 b it -1 mf# f unction 0 0 op2# (default) 0 1 baudout# 1 0 rxrdy# 1 1 reserved
xr xr16l2552 rev. 1.1.1 2.25v to 5.5v duart with 16-byte fifo 33 efr[3:0]: software flow control select single character and dual sequential characters software flow control is supported. combinations of software flow control can be selected by programming these bits. efr[4]: enhanced function bits enable enhanced function control bit. this bit enables ier bits 4-7, isr bits 4-5, and mcr bits 5-7 to be modified. after modifying any enhanced bits, efr bit-4 can be set to a logic 0 to latch the new values. this feature prevents legacy software from altering or overwriting the enhanced functions once set. normally, it is recommended to leave it enabled, logic 1. ? logic 0 = modification disable/latch enhanced features . ier bits 4-7, isr bits 4-5, and mcr bits 5-7 are saved to retain the user settings. after a reset, the ier bits 4-7, isr bits 4-5, and mcr bits 5-7are set to a logic 0 to be compatible with st16c550 mode (default). ? logic 1 = enables the above-mentioned register bits to be modified by the user. efr[5]: special character detect enable ? logic 0 = special character detect disabled (default). ? logic 1 = special character detect enabled. the ua rt compares each incomi ng receive character with data in xoff-2 register. if a match exists, the receive data will be transfer red to fifo and isr bit-4 will be set to indicate detection of the special character. bit-0 co rresponds with the lsb bit of the receive character. if flow control is set for comparing xon1, xo ff1 (efr [1:0]= ?10?) then flow control and special character work normally. however, if flow control is set for comparing xon2, xoff2 (efr[1:0]= ?01?) then flow control works normally, but xoff2 will not go to the fifo, and will ge nerate an xoff interrupt and a special character interrupt, if enabled via ier bit-5. special character interrupts are cleared automatically after the next received character. t able 12: s oftware f low c ontrol f unctions efr bit -3 c ont -3 efr bit -2 c ont -2 efr bit -1 c ont -1 efr bit -0 c ont -0 t ransmit and r eceive s oftware f low c ontrol 0 0 0 0 no tx and rx flow control (default and reset) 0 0 x x no transmit flow control 1 0 x x transmit xon1, xoff1 0 1 x x transmit xon2, xoff2 1 1 x x transmit xon1 and xon2, xoff1 and xoff2 x x 0 0 no receive flow control x x 1 0 receiver compares xon1, xoff1 x x 0 1 receiver compares xon2, xoff2 1 0 1 1 transmit xon1, xoff1 receiver compares xon1 or xon2, xoff1 or xoff2 0 1 1 1 transmit xon2, xoff2 receiver compares xon1 or xon2, xoff1 or xoff2 1 1 1 1 transmit xon1 and xon2, xoff1 and xoff2, receiver compares xon1 and xon2, xoff1 and xoff2 0 0 1 1 no transmit flow control, receiver compares xon1 and xon2, xoff1 and xoff2
xr16l2552 xr 2.25v to 5.5v duart with 16-byte fifo rev. 1.1.1 34 efr[6]: auto rts flow control enable rts# output may be used for hardware flow control by setting efr bit-6 to logic 1. when auto rts is selected, an interrupt will be generated when the receive fifo is filled to the pr ogrammed trigge r level and rts de-asserts to a logic 1 at the nex t upper trigger level. rts# will return to a logic 0 when fifo data falls below the next lower trigger level. the rts# output must be asserted (logic 0) before the auto rts can take effect. rts# pin will function as a general purpose output when hardware fl ow control is disabled. ? logic 0 = automatic rts flow control is disabled (default). ? logic 1 = enable automatic rts flow control. efr[7]: auto cts flow control enable automatic cts flow control. ? logic 0 = automatic cts flow control is disabled (default). ? logic 1 = enable automatic cts flow control. data tr ansmission stops when cts# input de-asserts to logic 1. data transmission resumes wh en cts# returns to a logic 0. 4.17 software flow control registers (xoff1, xoff2, xon1, xon2) - read/write these registers are used as the programmable software flow control characters xoff1, xoff2, xon1, and xon2. for more details, see ta b l e 6 .
xr xr16l2552 rev. 1.1.1 2.25v to 5.5v duart with 16-byte fifo 35 t able 13: uart reset conditio ns for channels a and b registers reset state dll bits 7-0 = 0xxx dlm bits 7-0 = 0xxx afr bits 7-0 = 0x00 rhr bits 7-0 = 0xxx thr bits 7-0 = 0xxx ier bits 7-0 = 0x00 fcr bits 7-0 = 0x00 isr bits 7-0 = 0x01 lcr bits 7-0 = 0x00 mcr bits 7-0 = 0x00 lsr bits 7-0 = 0x60 msr bits 3-0 = logic 0 bits 7-4 = logic levels of the inputs inverted spr bits 7-0 = 0xff efr bits 7-0 = 0x00 xon1 bits 7-0 = 0x00 xon2 bits 7-0 = 0x00 xoff1 bits 7-0 = 0x00 xoff2 bits 7-0 = 0x00 i/o signals reset state tx logic 1 mf# logic 1 rts# logic 1 dtr# logic 1 txrdy# logic 0 int logic 0 typical package thermal resistance data (margin of error: 15%) thermal resistance (48-tqfp) theta-ja =59 o c/w, theta-jc = 16 o c/w thermal resistance (44-plcc) theta-ja = 50 o c/w, theta-jc = 21 o c/w
xr16l2552 xr 2.25v to 5.5v duart with 16-byte fifo rev. 1.1.1 36 electrical characteristics test 1: the following inputs must remain steady at vc c or gnd state to minimize sleep current: a0-a2, d0- d7, ior#, iow#, cs#, chsel, and all modem inputs. also, rxa and rxb inputs must idle at logic 1 state while asleep. floating inputs will result in sleep currents in the ma range. for powersave feature that isolates address, data and control signals, please see the xr16l2551 datasheet. absolute maximum ratings power supply range 7 volts voltage at any pin gnd-0.3 v to vcc+0.3 v operating temperature -40 o to +85 o c storage temperature -65 o to +150 o c package dissipation 500 mw dc electrical characteristics unless otherwise noted: 40 o to +85 o c for industrial grade pack age, vcc is 2.25 to 5.5v s ymbol p arameter l imits 2.5v m in m ax l imits 3.3v m in m ax l imits 5.0v m in m ax u nits c onditions v ilck clock input low level -0.3 0.2 -0.3 0.6 -0.5 0.6 v v ihck clock input high level 2.0 5.5 2.4 5.5 3.0 5.5 v v il input low voltage -0.3 0.6 -0.3 0.8 -0.5 0.8 v v ih input high voltage 2.0 5.5 2.0 5.5 2.2 5.5 v v ol output low voltage 0.4 0.4 0.4 v v v i ol = 6 ma i ol = 4 ma i ol = 2 ma v oh output high voltage 1.8 2.0 2.4 v v v i oh = -6 ma i oh = -1 ma i oh = -400 ua i il input low leakage current 10 10 10 ua i ih input high leakage current 10 10 10 ua c in input pin capacitance 5 5 5 pf i cc power supply current 1 1.3 3 ma i sleep sleep current 6 15 30 ua see test 1
xr xr16l2552 rev. 1.1.1 2.25v to 5.5v duart with 16-byte fifo 37 ac electrical characteristics unless otherwise noted: ta=-40 o to +85 o c, vcc is 2.25v to 5.5v, 70 pf load where applicable s ymbol p arameter l imits 2.5 m in m ax l imits 3.3 m in m ax l imits 5.0 m in m ax u nit - crystal frequency 16 20 24 mhz clk external clock low/high time 31 17 10 ns osc external clock frequency 16 30 50 mhz t as address setup time 10 10 10 ns t ah address hold time 10 10 10 ns t cs chip select width 150 75 50 ns t rd ior# strobe width 150 75 50 ns t dy read cycle delay 150 75 50 ns t rdv data access time 125 70 45 ns t dd data disable time 0 45 0 30 0 30 ns t wr iow# strobe width 150 75 50 ns t dy write cycle delay 150 75 50 ns t ds data setup time 25 20 15 ns t dh data hold time 15 10 10 ns t wdo delay from iow# to output 150 75 50 ns t mod delay to set interrupt from modem input 150 75 50 ns t rsi delay to reset interrupt from ior# 150 75 50 ns t ssi delay from stop to set interrupt 1 1 1 bclk t rri delay from ior# to reset interrupt 150 75 50 ns t si delay from stop to interrupt 150 75 50 ns t int delay from initial int reset to transmit start 8 24 8 24 8 24 bclk t wri delay from iow# to reset interrupt 150 75 50 ns t ssr delay from stop to set rxrdy# 1 1 1 bclk t rr delay from ior# to reset rxrdy# 150 75 50 ns t wt delay from iow# to set txrdy# 150 75 50 ns t srt delay from center of start to reset txrdy# 8 8 8 bclk
xr16l2552 xr 2.25v to 5.5v duart with 16-byte fifo rev. 1.1.1 38 t rst reset pulse width 40 40 40 ns n baud rate divisor 1 2 16 -1 1 2 16 -1 1 2 16 -1 - bclk baud clock 16x of data rate hz f igure 14. c lock t iming f igure 15. m odem i nput /o utput t iming f or c hannels a & b ac electrical characteristics unless otherwise noted: ta=-40 o to +85 o c, vcc is 2.25v to 5.5v, 70 pf load where applicable s ymbol p arameter l imits 2.5 m in m ax l imits 3.3 m in m ax l imits 5.0 m in m ax u nit osc clk clk external clock iow # rts# dtr# cd# cts# dsr# int ior# ri# t wdo t mod t mod t rsi t mod active active change of state change of state active active active change of state change of state change of state active active
xr xr16l2552 rev. 1.1.1 2.25v to 5.5v duart with 16-byte fifo 39 f igure 16. d ata b us r ead t iming f igure 17. d ata b us w rite t iming t as t dd t ah t rd t rdv t dy t dd t rdv t ah t as t cs valid address valid address valid data valid data a0-a2 csa#/ csb# ior# d0-d7 rdtm t cs t rd 16write t as t dh t ah t wr t ds t dy t dh t ds t ah t as t cs valid address valid address valid data valid data a0-a2 csa#/ csb# iow# d0-d7 t cs t wr
xr16l2552 xr 2.25v to 5.5v duart with 16-byte fifo rev. 1.1.1 40 f igure 18. r eceive r eady & i nterrupt t iming [n on -fifo m ode ] for c hannels a & b f igure 19. t ransmit r eady & i nterrupt t iming [n on -fifo m ode ] for c hannels a & b rx rxrdy# ior# int d0:d7 start bit d0:d7 stop bit d0:d7 t ssr 1 byte in rhr active data ready active data ready active data ready 1 byte in rhr 1 byte in rhr t ssr t ssr rxnfm t rr t rr t rr t ssr t ssr t ssr (reading data out of rhr) tx txrdy# iow# int* d0:d7 start bit d0:d7 stop bit d0:d7 t wt txnonfifo t wt t wt t wri t wri t wri t srt t srt t srt *int is cleared when the isr is read or when data is loaded into the thr. isr is read isr is read isr is read (loading data into thr) (unloading) ier[1] enabled
xr xr16l2552 rev. 1.1.1 2.25v to 5.5v duart with 16-byte fifo 41 f igure 20. r eceive r eady & i nterrupt t iming [fifo m ode , dma d isabled ] for c hannels a & b f igure 21. r eceive r eady & i nterrupt t iming [fifo m ode , dma e nabled ] for c hannels a & b rx rxrdy# ior# int d0:d7 s t ssr rxintdma# rx fifo fills up to rx trigger level or rx data timeout rx fifo drops below rx trigger level fifo empties first byte is received in rx fifo d0:d7 s d0:d7 t d0:d7 s d0:d7 s t d0:d7 s t t d0:d7 s t start bit stop bit t rr t rri t ssi (reading data out of rx fifo) rx rxrdy# ior# int d0:d7 s t ssr rxfifodma rx fifo fills up to rx trigger level or rx data timeout rx fifo drops below rx trigger level fifo empties d0:d7 s d0:d7 t d0:d7 s d0:d7 s t d0:d7 s t t d0:d7 s t start bit stop bit t rr t rri t ssi (reading data out of rx fifo)
xr16l2552 xr 2.25v to 5.5v duart with 16-byte fifo rev. 1.1.1 42 f igure 22. t ransmit r eady & i nterrupt t iming [fifo m ode , dma m ode d isabled ] for c hannels a & b f igure 23. t ransmit r eady & i nterrupt t iming [fifo m ode , dma m ode e nabled ] for c hannels a & b tx txrdy# iow# int* txdma# d0:d7 s d0:d7 t d0:d7 s d0:d7 s t d0:d7 s t t d0:d7 s t start bit stop bit t wri (unloading) (loading data into fifo) last data byte transmitted tx fifo no longer empty data in tx fifo tx fifo empty t wt t srt tx fifo empty t t s t si isr is read ier[1] enabled *int is cleared when the isr is read or when there is at least one character in the fifo. tx txrdy# iow# int* txdma d0:d7 s d0:d7 t d0:d7 s d0:d7 s t d0:d7 s t t d0:d7 s t start bit stop bit t wri (unloading) (loading data into fifo) last data byte transmitted tx fifo no longer empty tx fifo empty tx fifo empty t t s t si isr is read ier[1] enabled *int is cleared when the isr is read or when there is at least one character in the fifo. at least 1 empty location in fifo t srt tx fifo full t wt
xr xr16l2552 rev. 1.1.1 2.25v to 5.5v duart with 16-byte fifo 43 package dimensions (48 pin tqfp - 7 x 7 x 1 mm ) note: the control dimensio n is the millimeter column inches millimeters symbol min max min max a 0.039 0.047 1.00 1.20 a1 0.002 0.006 0.05 0.15 a2 0.037 0.041 0.95 1.05 b 0.007 0.011 0.17 0.27 c 0.004 0.008 0.09 0.20 d 0.346 0.362 8.80 9.20 d1 0.272 0.280 6.90 7.10 e 0.020 bsc 0.50 bsc l 0.018 0.030 0.45 0.75 0 7 0 7 36 25 24 13 1 1 2 37 48 d d 1 d d 1 b e a 2 a 1 a seating plane l c
xr16l2552 xr 2.25v to 5.5v duart with 16-byte fifo rev. 1.1.1 44 package dimensions (44 pin plcc) note: the control dimensio n is the millimeter column inches millimeters symbol min max min max a 0.165 0.180 4.19 4.57 a1 0.090 0.120 2.29 3.05 a2 0.020 --- 0.51 --- b 0.013 0.021 0.33 0.53 b 1 0.026 0.032 0.66 0.81 c 0.008 0.013 0.19 0.32 d 0.685 0.695 17.40 17.65 d1 0.650 0.656 16.51 16.66 d 2 0.590 0.630 14.99 16.00 d 3 0.500 typ. 12.70 typ. e 0.050 bsc 1.27 bsc h 1 0.042 0.056 1.07 1.42 h 2 0.042 0.048 1.07 1.22 r 0.025 0.045 0.64 1.14 44 lead plastic leaded chip carrier (plcc) rev. 1.00 1 d d 1 a a 1 d d 1 d 3 b a 2 b 1 e seating plane d 2 244 d 3 c r 45 x h 2 45 x h 1
xr xr16l2552 rev. 1.1.1 2.25v to 5.5v duart with 16-byte fifo 45 notice exar corporation reserves the right to make changes to the products contained in this publicat ion in order to improve design, performanc e or reliability. exar corp oration assumes no responsibility for the use of any circuits described herein, conveys no license under any patent or other right, and makes no representation that the circuits are free of patent in fringement. charts and sc hedules contained here in are only for illustration purposes and may vary depending upon a user?s specific application. while the information in this publication has been carefully ch ecked; no responsibility, however , is assumed for inaccuracies. exar corporation does not re commend the use of any of its products in life suppo rt applications where the failure or malfunction of the product can reasonably be ex pected to cause failure of the life support system or to significantly affect its safety or effectiveness. products ar e not authorized for use in such applications unless exar corporation receives , in writing, assurances to its satisfaction that: (a) the ri sk of injury or damage has been minimized; (b) the us er assumes all such risks; (c) potential liability of exar corporation is adequately protected under the circumstances. copyright 2005 exar corporation datasheet may 2005. send your uart technical inquiry with technical details to hotline: uarttechsupport@exar.com . reproduction, in part or whole, without the prior written consent of exar co rporation is prohibited. revision history d ate r evision d escription november 2002 p1.0.0 preliminary datasheet. march 2003 p1.0.1 updated ac electrical characteristics. u pdated register set with enhanced features. may 2003 p1.0.2 added patent number to first page. june 2003 p1.0.3 added device status to ordering information. july 2003 p1.0.4 updated ac electrical characteristics. september 2003 1.0.0 final production release. updated 5v tolerance information. september 2004 1.1.0 corrected a2 and a0 pin numbers for plcc-44 package in pin descriptions. added device revision a nd device id registers and descriptions. may 2005 1.1.1 updated the data access time (t rdv ) in ac electrical characteristics.
xr16l2552 xr 2.25v to 5.5v duart with 16-byte fifo rev. 1.1.1 i table of contents general description ......... ................ ................ ................. .............. .............. ...........1 a pplications ............................................................................................................................... .................1 f eatures ............................................................................................................................... ......................1 f igure 1. xr16l2552 b lock d iagram ............................................................................................................................... .......... 1 f igure 2. p in o ut a ssignments ............................................................................................................................... .................... 2 ordering information ............................................................................................................................... ..2 pin descriptions ............ ................ ................. ................ ................. ................ ...........3 1.0 product description ..................................................................................................... ................6 2.0 functional descriptions ................................................................................................. ............7 2.1 cpu interface ........................................................................................................... ................................... 7 f igure 3. xr16l2552 d ata b us i nterconnections .................................................................................................................. 7 2.2 5-volt tolerant inputs ..... .............. .............. .............. .............. .............. .............. ......... ......................... 7 2.3 device reset .... .............. .............. .............. .............. .............. .............. ........... ......... .................................... 7 2.4 device identification and revision ........... ........................................................................... ............... 7 2.5 channel a and b selection .... .............. .............. .............. .............. .............. ........... .......... ..................... 8 t able 1: c hannel a and b s elect ............................................................................................................................... ................ 8 2.6 channel a and b internal registers ................. .............. .............. .............. .............. ............. .......... 8 2.7 simultaneous write to channel a and b .......... .............. .............. ........... ............ ........... ........... ...... 8 2.8 dma mode ................................................................................................................ ....................................... 8 t able 2: txrdy# and rxrdy# o utputs in fifo and dma m ode ............................................................................................. 9 2.9 inta and intb ouputs .................................................................................................... ............................ 9 t able 3: inta and intb p ins o peration for t ransmitter ........................................................................................................ 9 t able 4: inta and intb p in o peration f or r eceiver ............................................................................................................... 9 2.10 crystal oscillator or external clock input ........................................................................... 9 f igure 4. t ypical oscillator connections ............................................................................................................................... 10 2.11 programmable baud rate generat or ............ .............. .............. .............. ........... ............ .......... .. 10 f igure 5. e xternal c lock c onnection for e xtended d ata r ate .......................................................................................... 10 f igure 6. o perating f requency c hart . r equires a 2k ohms pull - up resistor on xtal2 pin to increase operating speed 11 t able 5: t ypical data rates with a 14.7456 mh z crystal or external clock ...................................................................... 11 2.12 transmitter ........ .............. .............. .............. .............. ........... ............ ........... .......... ................................. 12 2.12.1 transmit holding register (thr) - write only .......................................................................... ............. 12 2.12.2 transmitter operatio n in non-fifo mode ................................................................................ ................ 12 f igure 7. t ransmitter o peration in non -fifo m ode .............................................................................................................. 12 2.12.3 transmitter operation in fifo mode .................................................................................... ..................... 12 f igure 8. t ransmitter o peration in fifo and f low c ontrol m ode ..................................................................................... 13 2.13 receiver ............................................................................................................... ..................................... 13 2.13.1 receive holding register (rhr) - read-only ............................................................................ .............. 13 f igure 9. r eceiver o peration in non -fifo m ode .................................................................................................................... 14 f igure 10. r eceiver o peration in fifo and a uto rts f low c ontrol m ode ....................................................................... 14 2.14 auto rts (hardware) flow co ntrol ........... .............. .............. .............. .............. ........... ......... ...... 15 2.15 auto cts flow control ................................................................................................. .................... 15 f igure 11. a uto rts and cts f low c ontrol o peration ....................................................................................................... 16 2.16 auto xon/xoff (software) flow control .................................................................................. . 17 t able 6: a uto x on /x off (s oftware ) f low c ontrol ............................................................................................................... 17 2.17 special character detect .. ............. .............. .............. .............. .............. .............. ......... ................. 17 2.18 infrared mode ...... .............. .............. .............. .............. ........... ........... ............ .......... .............................. 18 f igure 12. i nfrared t ransmit d ata e ncoding and r eceive d ata d ecoding .......................................................................... 18 2.19 sleep mode with auto wake-u p ............ .............. .............. .............. .............. ........... ........... ............. 19 2.20 internal loopback ..................................................................................................... ......................... 20 f igure 13. i nternal l oop b ack in c hannel a and b ................................................................................................................ 20 3.0 uart internal registers ................................................................................................. ..........21 t able 7: uart channel a and b uart internal registers............................................................................ .......... 21 t able 8: internal registers description. s haded bits are enabled when efr b it -4=1......................................... 22 4.0 internal register descriptions .......................................................................................... ...23 4.1 receive holding register (rhr) - read- only .. .............. .............. .............. ........... ............ .......... .. 23 4.2 transmit holding register (thr) - write-only ............................................................................ 23 4.3 baud rate generator divisors (dll and dlm) - read/write .. .............. .............. .............. ....... 23 4.4 interrupt enable register (ier ) - read/write .......... .............. .............. .............. .............. .......... .. 23
xr xr16l2552 rev. 1.1.1 2.25v to 5.5v duart with 16-byte fifo ii 4.4.1 ier versus receive fifo interrupt mode operation ....................................................................... ...... 23 4.4.2 ier versus receive/transmit fifo polled mode operation................................................................ 24 4.5 interrupt status register (isr) - read-only ............................................................................. .. 25 4.5.1 interrupt generation: .................................................................................................. .................................... 25 4.5.2 interrupt clearing: .................................................................................................... ....................................... 25 t able 9: i nterrupt s ource and p riority l evel ....................................................................................................................... 26 4.6 fifo control register (fcr) - write-only ................................................................................ ..... 26 t able 10: r eceive fifo t rigger l evel s election ................................................................................................................... 27 4.7 line control register (lcr) - read/write ................................................................................ ..... 27 t able 11: p arity selection ............................................................................................................................... ......................... 28 4.8 modem control register (mcr) or gene ral purpose outputs control - read/write 28 4.9 line status register (lsr) - read only .................................................................................. ......... 29 4.10 modem status register (msr) - read only ................................................................................ .. 30 4.11 scratch pad register (spr) - read/write ................................................................................ .... 31 4.12 baud rate generator registers (dll and dlm) - read/write ....... ........... ............ ........... ..... 31 4.13 alternate function register (afr) - read/write ..................................................................... 31 4.14 device identification register (dvid) - read only .................................................................... 3 2 4.15 device revision register (drev) - read only ............................................................................ .. 32 4.16 enhanced feature register (efr) ........................................................................................ .......... 32 t able 12: s oftware f low c ontrol f unctions ........................................................................................................................ 33 4.17 software flow control registers (xoff1, xoff2, xon1, xon2) - read/write ................ 34 t able 13: uart reset conditions for channels a and b ............................................................................... .......... 35 t ypical package thermal resistance data (m argin of error : 15%) ................................................ 35 a bsolute m aximum r atings ..................................................................................................................... 36 electrical characteristics....... ................. ................ .............. .............. ............ 36 dc e lectrical c haracteristics .............................................................................................................. 36 ac e lectrical c haracteristics .............................................................................................................. 37 f igure 14. c lock t iming ............................................................................................................................... .............................. 38 f igure 15. m odem i nput /o utput t iming f or c hannels a & b ................................................................................................. 38 f igure 17. d ata b us w rite t iming ............................................................................................................................... ............. 39 f igure 16. d ata b us r ead t iming ............................................................................................................................... ............... 39 f igure 18. r eceive r eady & i nterrupt t iming [n on -fifo m ode ] for c hannels a & b ......................................................... 40 f igure 19. t ransmit r eady & i nterrupt t iming [n on -fifo m ode ] for c hannels a & b ....................................................... 40 f igure 20. r eceive r eady & i nterrupt t iming [fifo m ode , dma d isabled ] for c hannels a & b........................................ 41 f igure 21. r eceive r eady & i nterrupt t iming [fifo m ode , dma e nabled ] for c hannels a & b......................................... 41 f igure 22. t ransmit r eady & i nterrupt t iming [fifo m ode , dma m ode d isabled ] for c hannels a & b ........................... 42 f igure 23. t ransmit r eady & i nterrupt t iming [fifo m ode , dma m ode e nabled ] for c hannels a & b ............................ 42 package dimensions (48 pin tq fp - 7 x 7 x 1 mm) . ................. ................ ............ 43 package dimensions (44 pin plcc ) ................. .............. .............. .............. ............ 44 r evision h istory ............................................................................................................................... ....... 45 t able of c ontents .............. ................ ................ ................. ................ ................. ............ i

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