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exar corporation 48720 kato road, fremont ca, 94538 ? (510) 668-7000 ? fax (510) 668-7017 ? www.exar.com ? ? ? ? XR16L2551 low voltage duart with powersave september 2003 rev. 1.0.0 generageneral description the XR16L2551 (l2551) is a low voltage dual universal asynchronous receiver and transmitter (uart) with 5 volt tolerant inputs. the device includes additional capability over the st16c2550: intel and motorola data bus interface selection, hardware and software flow control, infrared encoder/ decoder, sleep mode and a powersave mode for battery operation. the l2551s enhanced register set is compatible to the st16c2550 and xr16l2550. it supports the exars enhanced features of 16 bytes of tx and rx fifos and a complete modem interface. onboard registers provide the user with operational status and data error tags. an internal loopback capability allows onboard diagnostics. independent programmable baud rate generator is provided in each channel to support data rates up to 3.125 mbps. n ote : 1 covered by u.s. patent #5,649,122. applications battery operated instruments data port adapters handheld appliances radio frequency data modems base stations usb hubs industrial automation controls features 2.25 to 5.5 volt operation 5 volt tolerant inputs intel or motorola bus interface select (16/68#) pin pin-to-pin compatible to xr16l2751cm two independent uarts n up to 3.125 mbps at 5v, 2 mbps at 3.3v, and 1 mbps at 2.5v with external clock input n up to 1.5 mbps at 5v, 1.25 mbps at 3.3v and 1 mbps at 2.5v with crystal clock input n 16 bytes of transmit and receive fifos n automatic rts/cts hardware flow control n automatic xon/xoff software flow control n wireless infrared encoder/decoder n receive fifo trigger levels select n programmable character lengths (5, 6, 7 or 8) with even, odd, forced or no parity n full modem interface (cts#, rts#, dsr#, dtr#, ri#, cd#) in the 48-tqfp package sleep mode with powersave feature for battery operation industrial temperature range tiny 32-qfn, no lead package (5x5x0.9mm) 48-tqfp package f igure 1. XR16L2551 b lock d iagram xtal1 xtal2 crystal osc/buffer txa, rxa, rtsa#, ctsa#, ( dtr#, dsr# cd#, ria#, op2a# ) intel or motorola data bus interface uart channel a 16 byte tx fifo 16 byte rx fifo brg ir endec tx & rx uart regs 2.25 to 5.5 volt vcc gnd *5 volt tolerant inputs 2551blk uart channel b (same as channel a) a2:a0 d7:d0 csa# (cs#) 16/68# csb# (a3) inta (irq#) intb (logic 0) pwrsave iow# (r/w#) ior# (vcc) reset (reset#) txrdya# txrdyb# rxrdya# rxrdyb# txb, rxb, rtsb#, ctsb#, ( dtrb#, dsrb# cdb#, rib#, op2b# )
XR16L2551 ? ? ? ? low voltage duart with powersave rev. 1.0.0 2 f igure 2. p in o ut a ssignment ordering information p art n umber p ackage o perating t emperature r ange d evice s tatus XR16L2551il 32-lead qfn -40c to +85c active XR16L2551im 48-lead tqfp -40c to +85c active 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 rxb rxa txrdyb# txa txb op2b# csa# csb# pwrsave xtal1 xtal2 iow# cdb# gnd rxrdyb# ior# dsrb# rib# rtsb# ctsb# 16/68# reset dtrb# dtra# rtsa# op2a# rxrdya# inta intb a0 a1 a2 nc d4 d3 d2 d1 d0 txrdya# vcc ria# cda# dsra# ctsa# XR16L2551 48-pin tqfp in 16 (intel) mode vcc nc 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 rxb rxa txrdyb# txa txb op2b# cs# a3 pwrsave xtal1 xtal2 iow# cdb# gnd rxrdyb# vcc dsrb# rib# rtsb# ctsb# 16/68# reset# dtrb# dtra# rtsa# op2a# rxrdya# irq# nc a0 a1 a2 nc d4 d3 d2 d1 d0 txrdya# vcc ria# cda# dsra# ctsa# nc XR16L2551 48-pin tqfp in 68 (motorola) mode) gnd 32 31 30 29 1 2 3 4 5 6 7 8 24 23 22 21 20 19 11 12 13 14 15 16 9 10 d5 d6 d7 rxb rxa txa txb csa# csb# xtal1 xtal2 iow# gnd ior# rtsb# ctsb# reset rtsa# inta intb a0 a1 a2 d4 d3 d2 d1 d0 vcc ctsa# XR16L2551 32-pin qfn in 16 (intel) mode 28 27 26 25 18 17 pwrsave 16/68# vcc 32 31 30 29 1 2 3 4 5 6 7 8 24 23 22 21 20 19 11 12 13 14 15 16 9 10 d5 d6 d7 rxb rxa txa txb cs# a3 (csb#) xtal1 xtal2 r/w# gnd vcc (ior#) rtsb# ctsb# reset# (reset) rtsa# irq# nc (intb) a0 a1 a2 d4 d3 d2 d1 d0 vcc ctsa# XR16L2551 32-pin qfn in 68 (motorola) mode 28 27 26 25 18 17 pwrsave 16/68# gnd
? ? ? ? XR16L2551 rev. 1.0.0 low voltage duart with powersave 3 pin descriptions pin description n ame 32-qfn p in # 48-tqfp p in # t ype d escription data bus interface a2 a1 a0 18 19 20 26 27 28 i address data lines [2:0]. these 3 address lines select one of the inter- nal registers in uart channel a/b during a data bus transaction. d7 d6 d5 d4 d3 d2 d1 d0 2 1 32 31 30 29 28 27 3 2 1 48 47 46 45 44 io data bus lines [7:0] (bidirectional). ior# (vcc) 14 19 i when 16/68# pin is at logic 1, the intel bus interface is selected and this input becomes read strobe (active low). the falling edge instigates an internal read cycle and retrieves the data byte from an internal register pointed by the address lines [a2:a0], puts the data byte on the data bus to allow the host processor to read it on the rising edge. when 16/68# pin is at logic 0, the motorola bus interface is selected and this input is not used and should be connected to vcc. iow# (r/w#) 12 15 i when 16/68# pin is at logic 1, it selects intel bus interface and this input becomes write strobe (active low). the falling edge instigates the inter- nal write cycle and the rising edge transfers the data byte on the data bus to an internal register pointed by the address lines. when 16/68# pin is at logic 0, the motorola bus interface is selected and this input becomes read (logic 1) and write (logic 0) signal. csa# (cs#) 7 10 i when 16/68# pin is at logic 1, this input is chip select a (active low) to enable channel a in the device. when 16/68# pin is at logic 0, this input becomes the chip select (active low) for the motorola bus interface. csb# (a3) 8 11 i when 16/68# pin is at logic 1, this input is chip select b (active low) to enable channel b in the device. when 16/68# pin is at logic 0, this input becomes address line a3 which is used for channel selection in the motorola bus interface. input logic 0 selects channel a and logic 1 selects channel b. inta (irq#) 22 30 o when 16/68# pin is at logic 1 for intel bus interface, this output becomes channel a interrupt output. the output state is defined by the user through the software setting of mcr[3]. inta is set to the active mode and op2a# output to a logic 0 when mcr[3] is set to a logic 1. inta is set to the three state mode and op2a# to a logic 1 when mcr[3] is set to a logic 0. see mcr[3]. when 16/68# pin is at logic 0 for motorola bus interface, this output becomes device interrupt output (active low, open drain). an external pull-up resistor is required for proper operation.
XR16L2551 ? ? ? ? low voltage duart with powersave rev. 1.0.0 4 intb (nc) 21 29 o when 16/68# pin is at logic 1 for intel bus interface, this output becomes channel b interrupt output. the output state is defined by the user and through the software setting of mcr[3]. intb is set to the active mode and op2b# output to a logic 0 when mcr[3] is set to a logic 1. intb is set to the three state mode and op2b# to a logic 1 when mcr[3] is set to a logic 0. see mcr[3]. when 16/68# pin is at logic 0 for motorola bus interface, this output is not used and will stay at logic zero level. leave this output uncon- nected. txrdya# - 43 o uart channel a transmitter ready (active low). the output provides the tx fifo/thr status for transmit channel a. if it is not used, leave it unconnected. rxrdya# - 31 o uart channel a receiver ready (active low). this output provides the rx fifo/rhr status for receive channel a. if it is not used, leave it unconnected. txrdyb# - 6 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 unconnected. rxrdyb# - 18 o uart channel b receiver ready (active low). this output provides the rx fifo/rhr status for receive channel b. if it is not used, leave it unconnected. modem or serial i/o interface txa 5 7 o uart channel a transmit data. if it is not used, leave it unconnected. rxa 4 5 i uart channel a 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. rtsa# 23 33 o uart channel a request-to-send (active low) or general purpose out- put. if it is not used, leave it unconnected. ctsa# 25 38 i uart channel a clear-to-send (active low) or general purpose input. this input should be connected to vcc when not used. dtra# - 34 o uart channel a data-terminal-ready (active low) or general purpose output. if it is not used, leave it unconnected. dsra# - 39 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 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 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. pin description n ame 32-qfn p in # 48-tqfp p in # t ype d escription
? ? ? ? XR16L2551 rev. 1.0.0 low voltage duart with powersave 5 op2a# - 32 o output port 2 channel a - the output state is defined by the user and through the software setting of mcr[3]. inta is set to the active mode and op2a# output to a logic 0 when mcr[3] is set to a logic 1. inta is set to the three state mode and op2a# to a logic 1 when mcr[3] is set to a logic 0. this output should not be used as a general output else it will disturb the inta output functionality. if it is not used at all, leave it unconnected. txb 6 8 o uart channel b transmit data. if it is not used, leave it unconnected. rxb 3 4 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# 15 22 o uart channel b request-to-send (active low) or general purpose out- put. if it is not used, leave it unconnected. ctsb# 16 23 i uart channel b clear-to-send (active low) or general purpose input. this input should be connected to vcc when not used. dtrb# - 35 o uart channel b data-terminal-ready (active low) or general purpose output. if it is not used, leave it unconnected. dsrb# - 20 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# - 16 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. rib# - 21 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. op2b# - 9 o output port 2 channel b - the output state is defined by the user and through the software setting of mcr[3]. intb is set to the active mode and op2b# output to a logic 0 when mcr[3] is set to a logic 1. intb is set to the three state mode and op2b# to a logic 1 when mcr[3] is set to a logic 0. this output should not be used as a general output else it will disturb the intb output functionality. if it is not used, leave it uncon- nected. ancillary signals xtal1 10 13 i crystal or external clock input. xtal2 11 14 o crystal or buffered clock output. 16/68# 17 24 i intel or motorola bus select. when 16/68# pin is at logic 1, 16 or intel mode, the device will operate in the intel bus type of interface. when 16/68# pin is at logic 0, 68 or motorola mode, the device will operate in the motorola bus type of interface. pin description n ame 32-qfn p in # 48-tqfp p in # t ype d escription
XR16L2551 ? ? ? ? low voltage duart with powersave rev. 1.0.0 6 pin type: i=input, o=output, io= input/output, od=output open drain. pwrsave 912i powersave (active high). this feature isolates the l2551s data bus interface from the host preventing other bus activities that cause higher power drain during sleep mode. see sleep mode with auto wake-up and powersave feature section for details. reset (reset#) 24 36 i when 16/68# pin is at logic 1 for intel bus interface, this input becomes reset (active high). when 16/68# pin is at logic 0 for motorola bus interface, this input becomes reset# (active low). a 40 ns minimum active pulse on this pin will reset the internal registers and all outputs of channel a and b. the uart transmitter output will be held at logic 1, the receiver input will be ignored and outputs are reset during reset period (see uart reset conditions). vcc 26 42 pwr 2.25v to 5.5v power supply. all inputs are 5v tolerant. gnd 13 17 pwr power supply common, ground. n.c. - 12, 25, 37 no connection. these pins are not connected internally. but if there is a possibility of migrating to the xr16l2751 for future needs, please refer to the xr16l2751 datasheet to determine if these pins should be connected to vcc or gnd. pin description n ame 32-qfn p in # 48-tqfp p in # t ype d escription
? ? ? ? XR16L2551 rev. 1.0.0 low voltage duart with powersave 7 1.0 product description the XR16L2551 (l2551) provides serial asynchronous receive data synchronization, parallel-to-serial and serial-to-parallel data conversions for both the transmitter and receiver sections. these functions are necessary for converting the serial data stream into parallel 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). data integrity is ensured by attaching a parity bit to the data character. the parity bit is checked by the receiver for any transmission bit errors. the electronic circuitry to provide all these functions is fairly complex especially when manufactured on a single integrated silicon chip. the l2551 represents such an integration with greatly enhanced features. the l2551 is fabricated with an advanced cmos process. transmit and receive fifos (16 bytes each) the l2551 is an upward solution that provides a dual uart capability with 16 bytes of transmit and receive fifo memory, instead of none in the 16c2450. the l2551 is designed to work with high speed modems and shared network environments, that require fast data processing time. increased performance is realized in the l2551 by the transmit and receive fifos. this allows the external processor to handle more networking tasks within a given time. for example, the st16c2450 without a receive fifo, will require unloading of the rhr in 93 microseconds (this example uses 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 l2551, the data buffer will not require unloading/loading for 1.53 ms. this increases the service interval giving the external cpu additional time 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, increases performance, and reduces power consumption. data bus interface, intel or motorola type the l2551 provides a single host interface for the 2 uarts and supports intel or motorola microprocessor (cpu) data bus interface. the intel bus compatible interface allows direct interconnect to intel compatible type of cpus using ior#, iow# and csa# or csb# inputs for data bus operation. the motorola bus compatible interface instead uses the r/w#, cs# and a3 signals for data bus transactions. few data bus interface signals change their functions depending on users selection, see pin description for details. the intel and motorola bus interface selection is made through the 16/68# pin (pin 24 for 48-tqfp package and pin 17 for 32-qfn package). enhanced features the XR16L2551 integrates the functions of 2 enhanced 16c550 universal asynchronous receiver and transmitter (uart). its features set is compatible to the xr16l2550 device but offers intel or motorola data bus interface and powersave to isolate the data bus interface during sleep mode. each uart is independently controlled having its own set of device configuration registers. the configuration registers set is 16550 uart 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 encoder and decoder (irda ver 1.0), programmable baud rate generator with a prescaler of divide by 1 or 4, and data rate up to 3.125 mbps at 5v with a 50 mhz external clock. the rich feature set of the l2551 is available through internal 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 (and operating in 16 or intel mode), the l2551 is functionally and software compatible with the previous generation st16c2450 and st16c2550.
XR16L2551 ? ? ? ? low voltage duart with powersave rev. 1.0.0 8 2.0 functional descriptions 2.1 cpu interface the cpu interface is 8 data bits wide with 3 address lines and control signals to execute data bus read and write transactions. the l2551 data interface supports the intel compatible types of cpus and it is compatible to the industry standard 16c550 uart. no clock (oscillator nor external clock) is required to operate a data bus transaction. each bus cycle is asynchronous using csa/b#, ior# and iow# or cs#, r/w# and a3 inputs. both uart channels share the same data bus for host operations. a typical data bus interconnection for intel and motorola mode is shown in figure 3 . 2.2 5-volt tolerant inputs the l2551 can accept up to 5v inputs even when operating at 3.3v or 2.5v. but note that if the l2551 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. f igure 3. xr16l2751 t ypical i ntel /m otorola d ata b us i nterconnections 2.25 to 5.5 volt 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_csa# uart_csb# ior# iow# d0 d1 d2 d3 d4 d5 d6 d7 a0 a1 a2 csa# csb# 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 intel data bus interconnections (no connect) (no connect) rs-232 serial interface 2.25 to 5.5 volt 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# a3 r/w# d0 d1 d2 d3 d4 d5 d6 d7 a0 a1 a2 csa# csb# d0 d1 d2 d3 d4 d5 d6 d7 ior# iow# uart channel a uart channel b uart_irq# intb inta rxrdya# txrdya# rxrdya# txrdya# rxrdyb# txrdyb# rxrdyb# txrdyb# reset# rs-232 serial interface rs-232 serial interface motorola data bus interconnections vcc uart_reset# (no connect) (no connect) (no connect) vcc
? ? ? ? XR16L2551 rev. 1.0.0 low voltage duart with powersave 9 2.3 device reset the reset or reset# input resets the internal registers and the serial interface outputs in both channels to their default state (see ta b l e 1 4 ). an active high pulse of at least 40 ns duration will be required to activate the reset function in the device. 2.4 channel a and b selection the uart provides the user with the capability to bi-directionally transfer information between an external cpu and an external serial communication device. a logic 0 on chip select pins, csa# or csb#, allows the user to select uart channel a or b to configure, send transmit data and/or unload receive data to/from the uart. selecting both uarts can be useful during power up initialization to write to the same internal registers, but do not attempt to read from both uarts simultaneously. individual channel select functions are shown in ta b l e 1 . during motorola bus mode (16/68# pin connected to gnd), the package interface pins are configured for connection with motorola, and other popular microprocessor bus types. in this mode the l2551 decodes an additional address, a3, to select one of the uart ports. the a3 address decode function is used only when in the motorola bus mode. see table 2 . channel a and b internal registers each uart channel in the l2551 has a standard register set for controlling, monitoring and data loading and unloading. the configuration register set is compatible to those already available in the standard single 16c550. these registers function as data holding registers (thr/rhr), interrupt status and control registers (isr/ier), a fifo control register (fcr), receive line status and control registers (lsr/lcr), modem status and control registers (msr/mcr), programmable data rate (clock) divisor registers (dll/dlm), and a user accessible scratch pad register (spr). 2.5 dma mode the device does not support direct memory access. the dma mode (a legacy term) in this document doesnt mean direct memory access but refers to data block transfer operation. the dma mode affects the state of the rxrdy# a/b and txrdy# a/b output pins. the transmit and receive fifo trigger levels provide additional flexibility 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 l2551 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 operation 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 20 through figure 25 . t able 1: c hannel a and b s elect in 16 m ode csa# csb# f unction 1 1 uart de-selected 0 1 channel a selected 1 0 channel b selected 0 0 channel a and b selected t able 2: c hannel a and b s elect in 68 m ode cs# a3 f unction 1 n/a uart de-selected 0 0 channel a selected 0 1 channel b selected
XR16L2551 ? ? ? ? low voltage duart with powersave rev. 1.0.0 10 2.6 inta and intb outputs the inta and intb interrupt output changes according to the operating mode and enhanced features setup. ta b l e 4 and ta b l e 5 summarize the operating behavior for the transmitter and receiver. also see figure 20 through figure 25 . 2.7 crystal oscillator or external clock input the l2551 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 require 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 xtal2 pin being the output. please note that the input xtal1 is not 5v tolerant and so the maximum at the pin should be vcc. for programming details, see programmable baud rate generator. t able 3: 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 time-out 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 4: 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 5: 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
? ? ? ? XR16L2551 rev. 1.0.0 low voltage duart with powersave 11 the on-chip oscillator is designed to use an industry standard microprocessor crystal (parallel resonant, fundamental frequency with 10-22 pf capacitance load, esr of 20-120 ohms and 100 ppm frequency tolerance) connected externally between the xtal1 and xtal2 pins (see figure 4 ), with an external 500 k w to 1 m w resistor across it. alternatively, an external clock can be connected to the xtal1 pin to clock the internal baud rate generator for standard or custom rates. typical oscillator connections are shown in figure 4 . for further reading on oscillator circuit please see application note dan108 on exars web site. 2.8 programmable baud rate generator a single baud rate generator is provided for the transmitter and receiver, allowing independent tx/rx channel control. the programmable baud rate generator is capable of operating with a crystal frequency of up to 24 mhz. however, with an external clock input on xtal1 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 w (optional) r2 500 k w - 1 m w xtal1 xtal2 2k xtal1 xtal2 r1 vcc external clock vcc gnd
XR16L2551 ? ? ? ? low voltage duart with powersave rev. 1.0.0 12 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 l2551 divides the basic external clock by 16. the basic 16x clock provides table rates to support standard and custom applications using the same system design. the baud rate generator divides the input 16x clock by any divisor from 1 to 2 16 -1. the rate table is configured via the dll and dlm internal register functions. customized baud rates can be achieved by selecting the proper divisor values for the msb and lsb sections of baud rate generator. ta b l e 6 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 external 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 resistor on xtal2 pin to increase operating speed divisor (decimal) = (xtal1 clock frequency) / (serial data rate x 16) 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 XR16L2551 with external clock and a 2k ohms pull-up resistor on xtal2 pin.
? ? ? ? XR16L2551 rev. 1.0.0 low voltage duart with powersave 13 2.9 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 periods. 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 fifo and tsr are reported in the line status register (lsr bit-5 and bit-6). 2.9.1 transmit holding register (thr) - write only the transmit holding register is an 8-bit register providing a data interface to the host processor. the host writes transmit data byte to the thr to be converted into a serial data stream including start-bit, data bits, parity-bit and stop-bit(s). the least-significant-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 enabled 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. 2.9.2 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 transmit empty interrupt (isr bit-1) when it is enabled by ier bit-1. the tsr flag (lsr bit-6) is set when tsr becomes completely empty. t able 6: 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 19.2k483000 300 38.4k241800 180 76.8k 12 0c 00 0c 0 153.6k 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
XR16L2551 ? ? ? ? low voltage duart with powersave rev. 1.0.0 14 2.9.3 transmitter operation in fifo mode the host may fill the transmit fifo with up to 16 bytes of transmit data. the thr empty flag (lsr bit-5) is set whenever the fifo is empty. the thr empty flag can generate 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. 2.10 receiver the receiver section contains an 8-bit receive shift register (rsr) and 16 bytes of fifo which includes a byte-wide receive holding register (rhr). the rsr uses the 16x for timing. 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 starts 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. evaluating the start bit in this manner prevents the receiver from assembling a false character. 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 receiving 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 time. this is equivalent to 3.7- 4.6 character times. the rhr interrupt is enabled by ier bit-0. f igure 7. t ransmitter o peration in non -fifo m ode f igure 8. t ransmitter o peration in fifo and f low c ontrol m ode 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 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
? ? ? ? XR16L2551 rev. 1.0.0 low voltage duart with powersave 15 2.10.1 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 for the 3 error tags to be reported in lsr register. when the fifo is enabled by fcr bit-0, the rhr contains the 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 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.
XR16L2551 ? ? ? ? low voltage duart with powersave rev. 1.0.0 16 2.11 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/resume 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). - 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. 2.12 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 auto cts flow control feature is selected to fit specific application requirement (see figure 11 ): - enable auto cts flow control using efr bit-7. - enable cts interrupt through ier bit-7 (after setting efr bit-4). the uart issues an interrupt when the cts# pin is de-asserted (logic 1): 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. transmission is resumed after the cts# input is re-asserted (logic 0), indicating more data may be sent.
? ? ? ? XR16L2551 rev. 1.0.0 low voltage duart with powersave 17 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 send data (3). txb data arrives and fills uarta receive fifo (4). when rxa data fills up to its receive fifo trigger level, uarta activates its rxa data ready interrupt (5) and con- tinues to receive and put data into its fifo. if interrupt service latency is long and data is not being unloaded, uarta monitors its receive data fill level to match the upper threshold of rts delay and de-assert rtsa# (6). ctsb# follows (7) and request uartb transmitter to suspend data transfer. uartb 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
XR16L2551 ? ? ? ? low voltage duart with powersave rev. 1.0.0 18 2.13 auto xon/xoff (software) flow control when software flow control is enabled ( see table 13 ), the l2551 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, the l2551 will halt transmission (tx) as soon as the current character has completed transmission. when a match occurs, the xoff (if enabled via ier bit-5) flag will be set and the interrupt output pin will be activated. following a suspension due to a match of the xoff character, the l2551 will monitor the receive data stream for a match to the xon-1,2 character. if a match is found, the l2551 will 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 control. different conditions can be set to detect xon/ xoff characters ( see table 13 ) and suspend/resume transmissions. when double 8-bit xon/xoff characters are selected, the l2551 compares two consecutive receive characters with two software flow control 8-bit values (xon1, xon2, xoff1, xoff2) and controls tx transmissions accordingly. under the above described flow control mechanisms, flow control characters are not placed (stacked) in the user accessible rx data buffer or fifo. in the event that the receive buffer is overfilling and flow control needs to be executed, the l2551 automatically sends an xoff message (when enabled) via the serial tx output to the remote modem. the l2551 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 programmed trigger level. to clear this condition, the l2551 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 ta b l e 7 below. * after the trigger level is reached, an xoff character is sent after a short span of time (= time required to send 2 characters); for example, after 2.083ms has elapsed for 9600 baud and 8-bit word length, no parity and 1 stop bit setting. 2.14 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 fifo along with normal incoming rx data. the l2551 compares each incoming receive character with xoff-2 data. if a match exists, the received data will be transferred to fifo and isr bit-4 will be set to indicate 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 length. 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 7: 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 ) 11 1* 0 44 4* 1 88 8* 4 14 14 14* 8
? ? ? ? XR16L2551 rev. 1.0.0 low voltage duart with powersave 19 2.15 infrared mode the l2551 uart includes the infrared encoder and decoder compatible to the irda (infrared data association) version 1.0. the irda 1.0 standard that stipulates the infrared encoder sends out a 3/16 of a bit wide high- pulse for each 0 bit in the transmit data stream. 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 mcr 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 returns 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-1 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
XR16L2551 ? ? ? ? low voltage duart with powersave rev. 1.0.0 20 2.16 sleep mode with auto wake-up and powersave feature the l2551 supports low voltage system designs, hence, a sleep mode with auto wake-up and powersave feature is included to reduce power consumption when the device is not actively used. 2.16.1 sleep mode all of these conditions must be satisfied for the l2551 to enter sleep mode: n no interrupts pending for both channels of the l2551 (isr bit-0 = 1) n divisor is a non-zero value (ie. dll = 0x1) n sleep mode of both channels are enabled (ier bit-4 = 1) n modem inputs are not toggling (msr bits 0-3 = 0) n rx input pins are idling at a logic 1 the l2551 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 l2551 resumes normal operation by any of the following when powersave mode is disabled (pin 12 at ground): n a receive data start bit transition (logic 1 to 0) n a data byte is loaded to the transmitter, thr or fifo n a change of logic state on any of the modem or general purpose serial inputs: cts#, dsr#, cd#, ri# if the l2551 is awakened by any one of the above conditions, it will return to the sleep mode automatically after all interrupting conditions have been serviced and cleared. if the l2551 is awakened by the modem inputs, a read to the msr is required to reset the modem inputs. in any case, the sleep mode will not be entered while an interrupt is pending from channel a or b. the l2551 will stay in the sleep mode of operation until it is disabled by setting ier bit-4 to a logic 0. a word of caution: owing to the starting up delay of the crystal oscillator after waking up from sleep mode, the first few receive characters may be lost. the number of characters lost during the restart also depends on your operating data rate. more characters are lost when operating at higher data rate. also, it is important to keep rx a/b inputs idling at logic 1 or marking condition during sleep mode to avoid receiving a break condition upon the restart. this may occur when the external interface transceivers (rs-232, rs-485 or another type) are also put to sleep mode and cannot maintain the marking condition. to avoid this, the designer can use a 47k-100k ohm pull-up resistor on the rxa and rxb pins. 2.16.2 powersave feature if the address lines, data bus lines, iow#, ior#, csa#, csb#, and modem input lines remain steady when the l2551 is in sleep mode, the maximum current will be in the microamp range as specified in the dc electrical characteristics on page 37 . if the input lines are floating or are toggling while the l2551 is in sleep mode, the current can be up to 100 times more. if not using the powersave feature, then an external buffer would be required to keep the address and data bus lines from toggling or floating to achieve the low current. but if the powersave feature is enabled (pin 12 of the 48-tqfp or pin 9 of the 32-qfn is connected to vcc), this will eliminate the need for an external buffer by internally isolating the address, data and control signals (see figure 1 on page 1) from other bus activities that could cause wasteful power drain. the l2551 enters powersave mode when the pwrsave pin is connected to vcc and the l2551 is in sleep mode (see sleep mode section above). since powersave mode isolates the address, data and control signals, the device will wake-up by: n a receive data start bit transition (logic 1 to 0) n a change of logic state on any of the modem or general purpose serial inputs: cts#, dsr#, cd#, ri# the l2551 will return to the powersave mode automatically after a read to the msr (to reset the modem inputs) and all interrupting conditions have been serviced and cleared. the l2551 will stay in the powersave mode of operation until it is disabled by setting ier bit-4 to a logic 0 and/or the powersave pin is connected to gnd.
? ? ? ? XR16L2551 rev. 1.0.0 low voltage duart with powersave 21 2.17 internal loopback the l2551 uart provides an internal loopback capability for system diagnostic purposes. the internal loopback mode is enabled by setting mcr register bit-4 to logic 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 receive 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 ignored. caution: the rx input pins must be held to a logic 1 during loopback test else upon exiting the loopback test the uart may detect 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#
XR16L2551 ? ? ? ? low voltage duart with powersave rev. 1.0.0 22 3.0 uart internal registers each of the uart channel in the l2551 has its own set of configuration registers selected by address lines a0, a1 and a2 with csa# or csb# selecting the channel. the registers are 16c550 compatible. the complete register set is shown on ta b l e 8 and ta b l e 9 .. . . internal register descriptions t able 8: 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 1 0xbf 0 0 1 dlm - div latch high byte 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 lcr 1 0xbf 0 1 1 lcr - line control register read/write 1 0 0 mcr - modem control register read/write lcr 1 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 t able 9: 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
? ? ? ? XR16L2551 rev. 1.0.0 low voltage duart with powersave 23 4.0 internal register descriptions 4.1 receive holding register (rhr) - read- only see receiver on page 14. 4.2 transmit holding register (thr) - write-only see transmitter on page 13. 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 lcr 1 0xbf 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 loop- back enable op2#/ int output enable rsvd (op1#) rts# output control dtr# output control lcr 1 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 1 0xbf 0 0 1 dlm rd/wr bit-7 bit-6 bit-5 bit-4 bit-3 bit-2 bit-1 bit-0 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 9: 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
XR16L2551 ? ? ? ? low voltage duart with powersave rev. 1.0.0 24 4.3 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 reported in the interrupt status register (isr). 4.3.1 ier versus receive fifo interrupt mode operation when the receive fifo (fcr bit-0 = 1) and receive interrupts (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 when 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 reset when the fifo is empty. 4.3.2 ier versus receive/transmit fifo polled mode operation when fcr bit-0 equals a logic 1 for fifo enable; resetting ier bits 0-3 enables the XR16L2551 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 errors encountered for the data byte in rhr, if any. d. lsr bit-5 indicates transmit 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.
? ? ? ? XR16L2551 rev. 1.0.0 low voltage duart with powersave 25 ier[0]: rhr interrupt enable the receive data ready interrupt will be issued when rhr has a data character in the 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 ready interrupt which is issued whenever the transmit fifo becomes empty. if the transmit fifo is empty when this bit is enabled, an interrupt will be generated. 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 interrupt 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 control, receive xoff interrupt. (default) logic 1 = enable the software flow control, receive xoff 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. 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. 4.4 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 highest pending interrupt level to be serviced, 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 1 0 , shows the data values (bit 0-5) for the interrupt priority levels and the interrupt sources associated with each of these interrupt levels.
XR16L2551 ? ? ? ? low voltage duart with powersave rev. 1.0.0 26 4.4.1 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 detection 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 the output pin (from low to high) during auto rts flow control enabled by efr bit-6. 4.4.2 interrupt clearing: lsr interrupt is cleared by a read to the lsr register (but 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 falls 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. ] 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 t able 10: 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)
? ? ? ? XR16L2551 rev. 1.0.0 low voltage duart with powersave 27 these bits indicate the source for a pending interrupt at interrupt priority levels (see interrupt source ta b l e 1 0 ).
XR16L2551 ? ? ? ? low voltage duart with powersave rev. 1.0.0 28 isr[4]: xoff or special character interrupt status this bit is enabled when efr bit-4 is set to a logic 1. isr 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 special character interrupt, it will automatically clear after 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 disabled. they are set to a logic 1 when the fifos are enabled. 4.5 fifo control register (fcr) - write-only this register is used to enable the fifos, clear the fifos, 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 level counter logic (the receive shift register is not cleared or altered). this bit will return to a logic 0 after resetting the fifo. 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 level 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 thetxrdy# 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 set the trigger level for the receive fifo. the uart will issue a receive interrupt when the number of the characters in the fifo crosses the trigger level. ta b l e 1 1 shows the complete selections.
? ? ? ? XR16L2551 rev. 1.0.0 low voltage duart with powersave 29 4.6 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 bit in conjunction with the programmed word length. lcr[3]: tx and rx parity select parity or no parity can be selected via this bit. the parity bit is a simple way used in communications for data integrity check. see ta b l e 1 2 for parity selection summary below. logic 0 = no parity. logic 1 = a parity bit is generated during the transmission 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 logic 1, lcr bit-4 selects the even or odd parity format. logic 0 = odd parity is generated by forcing an odd number of logic 1s in the transmitted character. the receiver must be programmed to check the same format (default). logic 1 = even parity is generated by forcing an even number of logic 1s in the transmitted character. the receiver must be programmed to check the same format. t able 11: 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 16c550, 16c2550, 16c2552, 16c554, 16c580 compatible. bit-1 bit-0 w ord length 0 0 5 (default) 01 6 10 7 11 8 bit-2 w ord length s top bit length (b it time ( s )) 0 5,6,7,8 1 (default) 15 1-1/2 16,7,8 2
XR16L2551 ? ? ? ? low voltage duart with powersave rev. 1.0.0 30 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 condition to be transmitted (the tx output is forced to a space, logic 0, state). this condition 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 (dll/dlm) enable logic 0 = data registers are selected (default). logic 1 = divisor latch registers are selected. 4.7 modem control register (mcr) or general purpose outputs control - read/write the mcr register is used for controlling the serial/modem interface signals or general purpose inputs/outputs. mcr[0]: dtr# output the dtr# pin is a modem control output. if the modem interface is not used, 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 interface 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]: reserved op1# is not available as an output pin on the l2551. 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. t able 12: 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 01 1 even parity 1 0 1 force parity to mark, 1 1 1 1 forced parity to space, 0
? ? ? ? XR16L2551 rev. 1.0.0 low voltage duart with powersave 31 mcr[3]: op2# output / int output enable this bit enables and disables the operation of int, interrupt output. if int output is not used, op2# can be used as a general purpose output. this bit does not affect the irq# output during motorola mode. logic 0 = int (a-b) outputs disabled (three state mode) and op2# output set to a logic 1 (default). logic 1 = int (a-b) outputs enabled (active mode) and op2# output set 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 compatibility, default). logic 1 = enable xon-any function. in this mode, any rx character received 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 l2551 is programmed to use the xon/xoff flow control. mcr[6]: infrared encoder/decoder enable logic 0 = enable the standard modem receive and 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 output 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. 4.8 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 saved in the receive holding register or fifo. 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 fifo 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. an interrupt will be generated immediately if lsr interrupt is enabled (ier bit-2). lsr[2]: receive data parity error flag logic 0 = no parity error (default). logic 1 = parity error. the receive character in rhr does not have correct parity information and is suspect. this error is associated with the character available for reading in rhr. if the lsr interrupt is enabled (ier bit-2), an interrupt will be generated when the character is in the rhr.
XR16L2551 ? ? ? ? low voltage duart with powersave rev. 1.0.0 32 lsr[3]: receive data framing error flag logic 0 = no framing error (default). logic 1 = framing error. the receive character did not have a valid stop bit(s). this error is associated with the character available for reading in rhr. if the lsr interrupt is enabled (ier bit-2), an interrupt will be generated when the character is in the rhr. lsr[4]: receive break flag 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. if the lsr interrupt is enabled (ier bit-2), an interrupt will be generated when the character is in the rhr. lsr[5]: transmit holding register empty flag this bit is the transmit holding register empty indicator. this bit indicates 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 interrupt 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 register. the bit is reset to logic 0 concurrently with the data loading to the transmit holding register by the host. in the fifo mode this bit is set when the transmit fifo is empty, it is cleared when the transmit 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 bit 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. 4.9 modem status register (msr) - read only this register provides the current state of the modem interface signals, or other 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 last time it was monitored. a modem status interrupt will be generated if msr interrupt is enabled (ier bit-3). 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 interrupt 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 ringing signal. a modem status interrupt will be generated if msr interrupt is enabled (ier bit-3).
? ? ? ? XR16L2551 rev. 1.0.0 low voltage duart with powersave 33 msr[3]: delta cd# input flag logic 0 = no change on cd# input (default). logic 1 = indicates that the cd# input has changed state 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 compliment 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. 4.10 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. 4.11 baud rate generator registers (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 only accessible when lcr bit-7 is set to 1. see programmable baud rate generator on page 11. for more details. 4.12 enhanced feature register (efr) enhanced features are enabled or disabled using this register. bit 0-3 provide single or dual consecutive character software flow control selection (see ta b l e 1 3 ). when the xon1 and xon2 and xoff1 and xoff2 modes are selected, the double 8-bit words are concatenated into 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.
XR16L2551 ? ? ? ? low voltage duart with powersave rev. 1.0.0 34 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 uart compares each incoming receive character with data in xoff-2 register. if a match exists, the receive data will be transferred to fifo and isr bit-4 will be set to indicate detection of the special character. bit-0 corresponds with the lsb bit of the receive character. if flow control is set for comparing xon1, xoff1 (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 generate 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. efr[6]: auto rts flow control enable t able 13: 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
? ? ? ? XR16L2551 rev. 1.0.0 low voltage duart with powersave 35 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 programmed trigger level and rts de- asserts to a logic 1 at the next 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 flow 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 transmission stops when cts# input de-asserts to logic 1. data transmission resumes when cts# returns to a logic 0. 4.13 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 7 .
XR16L2551 ? ? ? ? low voltage duart with powersave rev. 1.0.0 36 t able 14: uart reset conditions for channel a and b registers reset state dlm bits 7-0 = 0xxx dll bits 7-0 = 0xxx 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 op2# logic 1 rts# logic 1 dtr# logic 1 rxrdy# logic 1 txrdy# logic 0 int three-state condition
? ? ? ? XR16L2551 rev. 1.0.0 low voltage duart with powersave 37 test 1: the following inputs must remain steady at vcc or gnd state to minimize sleep current: a0-a2, d0-d7, ior#, iow# (r/w#), csa# (cs#), csb# (a3) and all modem inputs. also, rxa and rxb inputs must idle at logic 1 state while asleep. floating inputs may result in sleep currents in the ma range. for powersave, the uart internally isolates all of these inputs therefore not requiring them to remain steady. 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 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 (32-qfn) theta-ja = o c/w, theta-jc = o c/w electrical characteristics dc electrical characteristics u nless otherwise noted : ta=-40 o to +85 o c, v cc is 2.25 to 5.5v s ymbol p arameter 2.5v l imits m in m ax 3.3v l imits m in m ax 5.0v l imits 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 i pwrsv sleep current/ powersave current 61530uasee test 1
XR16L2551 ? ? ? ? low voltage duart with powersave rev. 1.0.0 38 ac electrical characteristics u nless otherwise noted : ta=-40 o to +85 o c, v cc is 2.25v to 5.5v, 70 p f 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 (16 mode) 10 10 10 ns t ah address hold time (16 mode) 10 10 10 ns t cs chip select width (16 mode) 150 75 50 ns t rd ior# strobe width (16 mode) 150 75 50 ns t dy read cycle delay (16 mode) 150 75 50 ns t rdv data access time (16 mode) 125 80 50 ns t dd data disable time (16 mode) 045030030ns t wr iow# strobe width (16 mode) 150 75 50 ns t dy write cycle delay (16 mode) 150 75 50 ns t ds data setup time (16 mode) 25 20 15 ns t dh data hold time (16 mode) 15 10 10 ns t ads address setup (68 mode) 10 10 10 ns t adh address hold (68 mode) 10 10 10 ns t rws r/w# setup to cs# (68 mode) 10 10 10 ns t rda read data access (68 mode) 175 100 60 ns t rdh read data disable (68 mode) 45 30 30 ns t wds write data setup (68 mode) 25 20 15 ns t wdh write data hold (68 mode) 15 10 10 ns t rwh r/w# hold (68 mode) 15 10 10 ns t csl cs# width (68 mode) 150 75 50 ns t csd cs# cycle delay (68 mode) 150 75 50 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
? ? ? ? XR16L2551 rev. 1.0.0 low voltage duart with powersave 39 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 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 ac electrical characteristics u nless otherwise noted : ta=-40 o to +85 o c, v cc is 2.25v to 5.5v, 70 p f 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
XR16L2551 ? ? ? ? low voltage duart with powersave rev. 1.0.0 40 f igure 15. m odem i nput /o utput t iming f or c hannels a & b f igure 16. 16 m ode (i ntel ) d ata b us r ead t iming 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 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
? ? ? ? XR16L2551 rev. 1.0.0 low voltage duart with powersave 41 f igure 17. 16 m ode (i ntel ) d ata b us w rite t iming f igure 18. 68 m ode (m otorola ) d ata b us r ead t iming 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 68read t ads t rdh t adh t csl t rda t csd t rws valid address valid address valid data a0-a3 cs# r/w# d0-d7 t rwh valid data
XR16L2551 ? ? ? ? low voltage duart with powersave rev. 1.0.0 42 f igure 19. 68 m ode (m otorola ) d ata b us w rite t iming f igure 20. r eceive r eady & i nterrupt t iming [n on -fifo m ode ] for c hannels a & b 68write t ads t adh t csl t wds t csd t rws valid address valid address valid data a0-a3 cs# r/w# d0-d7 t rwh valid data t wdh 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)
? ? ? ? XR16L2551 rev. 1.0.0 low voltage duart with powersave 43 f igure 21. t ransmit r eady & i nterrupt t iming [n on -fifo m ode ] for c hannels a & b f igure 22. r eceive r eady & i nterrupt t iming [fifo m ode , dma d isabled ] for c hannels a & b 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 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)
XR16L2551 ? ? ? ? low voltage duart with powersave rev. 1.0.0 44 f igure 23. r eceive r eady & i nterrupt t iming [fifo m ode , dma e nabled ] for c hannels a & b f igure 24. t ransmit r eady & i nterrupt t iming [fifo m ode , dma m ode d isabled ] for c hannels a & b 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) 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.
? ? ? ? XR16L2551 rev. 1.0.0 low voltage duart with powersave 45 f igure 25. 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 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
XR16L2551 ? ? ? ? low voltage duart with powersave rev. 1.0.0 46 package dimensions (48 pin tqfp - 7 x 7 x 1 mm ) note: the control dimension is the millimeter column inches millimeters symbol min max min max a 0.039 0.047 1.00 1.20 a 1 0.002 0.006 0.05 0.15 a 2 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 d 1 0.272 0.280 6.90 7.10 e 0.020 bsc 0.50 bsc l 0.018 0.030 0.45 0.75 a 0 7 0 7 36 25 24 13 1 1 2 37 48 d d 1 d d 1 b e a a 2 a 1 a seating plane l c
? ? ? ? XR16L2551 rev. 1.0.0 low voltage duart with powersave 47 package dimensions (32 pin qfn - 5 x 5 x 0.9 mm ) note: the control dimension is the millimeter column inches millimeters symbol min max min max a 0.031 0.039 0.80 1.00 a1 0.000 0.002 0.00 0.05 a3 0.006 0.010 0.15 0.25 d 0.193 0.201 4.90 5.10 d2 0.138 0.150 3.50 3.80 b 0.007 0.012 0.18 0.30 e 0.0197 bsc 0.050 bsc l 0.014 0.018 0.35 0.45 d d2 d2 b l d a steating plane a1 a3 e
XR16L2551 ? ? ? ? low voltage duart with powersave rev. 1.0.0 48 notice exar corporation reserves the right to make changes to the products contained in this publication in order to improve design, performance or reliability. exar corporation 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 infringement. charts and schedules contained here in are only for illustration purposes and may vary depending upon a users specific application. while the information in this publication has been carefully checked; no responsibility, however, is assumed for inaccuracies. exar corporation does not recommend the use of any of its products in life support applications where the failure or malfunction of the product can reasonably be expected to cause failure of the life support system or to significantly affect its safety or effectiveness. products are not authorized for use in such applications unless exar corporation receives, in writing, assurances to its satisfaction that: (a) the risk of injury or damage has been minimized; (b) the user assumes all such risks; (c) potential liability of exar corporation is adequately protected under the circumstances. copyright 2003 exar corporation datasheet september 2003. 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 corporation is prohibited. revision history date revision description november 2002 p1.0.0 preliminary datasheet. march 2003 p1.0.1 updated ac electrical characteristics. updated register set with enhanced fea- tures. may 2003 p1.0.2 added patent number to first page. added 32 pin qfn package dimensions. 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.

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