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exar corporation 48720 kato road, fremont ca, 94538 ? (510) 668-7000 ? fax (510) 668-7017 ? www.exar.com ? ? ? ? st16c2450 2.97v to 5.5v duart september 2003 rev. 4.0.0 general description the st16c2450 (2450) is a dual universal asynchro- nous receiver and transmitter (uart). the st16c2450 is an improved version of the st16c2450 with lower operating voltage and 5 volt tolerant inputs. the 2450 provides enhanced uart functions, a modem control interface and data rates up to 1.5 mbps. onboard status registers provide the user with error indications and operational status. in- dependent programmable baud rate generators are provided to select transmit and receive clock rates up to 1.5 mbps. an internal loopback capability allows onboard diagnostics. the 2450 is available in a 44- pin plcc and 48-pin tqfp packages. the 2450 is fabricated in an advanced cmos process capable of operating from 2.97 volt to 5.5 volt power supply. the devices with a top marking of "a2 yyww" or newer have 5 volt tolerant inputs. applications ? portable appliances ? telecommunication network routers ? ethernet network routers ? cellular data devices ? factory automation and process controls features added feature in devices with top marking "a2 yyww" and newer: n 5 volt tolerant inputs 2.97 to 5.5 volt operation pin-to-pin compatible to exars st16c2450, st16c2550, xr16l2550, xr16l2750 and xr16c2850 pin-to-pin compatible to tis tl16c752b on the 48- tqfp package 2 independent uart channels n up to 1.5 mbps data rate with a 24 mhz crystal oscillator or external clock frequency n 1 byte transmit fifo n 1 byte receive fifo with error tags n status report registers n modem control signals (cts#, rts#, dsr#, dtr#, ri#, cd#) n programmable character lengths (5, 6, 7, 8) with even, odd, or no parity crystal oscillator or external clock input ttl compatible inputs, outputs industrial temperature ranges 48-tqfp and 44-plcc packages f igure 1. st16c2450 b lock d iagram xtal1 xtal2 crystal osc/buffer txa, rxa, dtra#, dsra#, rtsa#, dtsa#, cda#, ria#, op2a# 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 txb, rxb, dtrb#, dsrb#, rtsb#, ctsb#, cdb#, rib#, op2b# uart channel b (same as channel a) a2:a0 d7:d0 csa# csb# inta intb iow# ior# reset
st16c2450 ? ? ? ? 2.97v to 5.5v duart rev. 4.0.0 2 f igure 2. p in o ut a ssignment 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 nc txa txb op2b# csa# csb# nc xtal1 xtal2 iow# cdb# gnd nc ior# dsrb# rib# rtsb# ctsb# nc reset dtrb# dtra# rtsa# op2a# nc inta intb a0 a1 a2 nc d4 d3 d2 d1 d0 nc vcc ria# cda# dsra# ctsa# nc st16c2450 48-pin tqfp 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 rxb rxa nc txa txb op2b# csa# csb# reset dtrb# dtra# rtsa# op2a# nc inta intb a0 a1 a2 xtal1 xtal2 iow# cdb# gnd nc ior# dsrb# rib# rtsb# ctsb# d4 d3 d2 d1 d0 nc vcc ria# cda# dsra# ctsa# st16c2450 44-pin plcc 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 40 39 38 37 36 35 34 33 32 31 30 29 28 27 26 25 24 23 22 21 d0 d1 d2 d3 d4 d5 d6 d7 rxb rxa txa txb op2b# csa# csb# xtal1 xtal2 iow# cdb# gnd vcc ria# cda# dsra# ctsa# reset dtrb# dtra# rtsa# op2a# inta intb a0 a1 a2 ctsb# rtsb# rib# dsrb# ior# st16c2450cp40
? ? ? ? st16c2450 rev. 4.0.0 2.97v to 5.5v duart 3 pin descriptions ordering information p art n umber p ackage o perating t emperature r ange d evice s tatus st16c2450cp40 40-lead pdip 0c to +70c active. see the st16c2450cq48 for new designs. st16c2450cj44 44-lead plcc 0c to +70c active st16c2450cq48 48-lead tqfp 0c to +70c active st16c2450ip40 40-lead pdip -40c to +85c active. see the st16c2450iq48 for new designs. st16c2450ij44 44-lead plcc -40c to +85c active st16c2450iq48 48-lead tqfp -40c to +85c active pin description n ame 44-plcc p in # 48-tqfp p in # t ype d escription data bus interface a2 a1 a0 29 30 31 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 9 8 7 6 5 4 3 2 3 2 1 48 47 46 45 44 io data bus lines [7:0] (bidirectional). ior# 24 19 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# 20 15 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. csa# 16 10 i uart channel a select (active low) to enable uart channel a in the device for data bus operation. csb# 17 11 i uart channel b select (active low) to enable uart channel b in the device for data bus operation. inta 33 30 o uart channel a interrupt output. 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 (default).
st16c2450 ? ? ? ? 2.97v to 5.5v duart rev. 4.0.0 4 intb 32 29 o uart 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 (default). modem or serial i/o interface txa 13 7 o uart channel a transmit data. if it is not used, leave it unconnected. rxa 11 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# 36 33 o uart channel a request-to-send (active low) or general purpose out- put. if it is not used, leave it unconnected. ctsa# 40 38 i uart channel a clear-to-send (active low) or general purpose input. this input should be connected to vcc when not used. this input has no effect on the uart. dtra# 37 34 o uart channel a data-terminal-ready (active low) or general purpose output. if it is not used, leave it unconnected. dsra# 41 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# 42 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# 43 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. op2a# 35 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 14 8 o uart channel b transmit data. if it is not used, leave it unconnected. rxb 10 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# 27 22 o uart channel b request-to-send (active low) or general purpose out- put. if it is not used, leave it unconnected. ctsb# 28 23 i uart channel b clear-to-send (active low) or general purpose input. this input should be connected to vcc when not used. this input has no effect on the uart. dtrb# 38 35 o uart channel b data-terminal-ready (active low) or general purpose output. if it is not used, leave it unconnected. pin description n ame 44-plcc p in # 48-tqfp p in # t ype d escription
? ? ? ? st16c2450 rev. 4.0.0 2.97v to 5.5v duart 5 pin type: i=input, o=output, io= input/output, od=output open drain. dsrb# 25 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# 21 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# 26 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# 15 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 18 13 i crystal or external clock input. xtal2 19 14 o crystal or buffered clock output. reset 39 36 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 out- put will be held at logic 1, the receiver input will be ignored and outputs are reset during reset period. vcc 44 42 pwr 2.97v to 5.5v power supply. all inputs are 5v tolerant for devices with top marking of "a2 yyww" and newer. gnd 22 17 pwr power supply common, ground. n.c. 1, 12, 23, 34 6, 12, 18, 24, 25, 31, 37, 43 - no connection. these pins are open, but typically, should be con- nected to gnd for good design practice. pin description n ame 44-plcc p in # 48-tqfp p in # t ype d escription
st16c2450 ? ? ? ? 2.97v to 5.5v duart rev. 4.0.0 6 1.0 product description the st16c2450 (2450) integrates the functions of two 16c450 universal asynchrounous receiver and transmitter (uart). each uart is independently controlled having its own set of device configuration registers. the 2450 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 stops 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 2450 represents such an integration with greatly enhanced features. the 2450 is fabricated with an advanced cmos process. the 2450 is capable of operation up to 1.5 mbps with a 24 mhz clock. with a crystal or external clock input of 14.7456 mhz the user can select data rates up to 921.6 kbps. 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 2450 data interface supports the intel compatible types of cpus and it is compatible to the industry standard 16c450 uart. no clock (oscillator nor external clock) is required to operate a data bus transaction. each bus cycle is asynchronous using 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 device reset the reset input resets the internal registers and the serial interface outputs in both channels to their default state (see ta b l e 8 ). an active high pulse of at least 40 ns duration will be required to activate the reset function in the device. f igure 3. st16c2450 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_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 uart_reset reset rs-232 serial interface rs-232 serial interface
? ? ? ? st16c2450 rev. 4.0.0 2.97v to 5.5v duart 7 2.3 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 . 2.4 channel a and b internal registers each uart channel in the 2450 has a standard register set for controlling, monitoring and data loading and unloading. these registers function as data holding registers (thr/rhr), interrupt status and control registers (isr/ier), 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 inta and intb outputs the inta and intb interrupt output changes according to the operating mode and enhanced features setup. ta b l e 2 summarizes the operating behavior for the transmitter and receiver. also see figure 12 and figure 13 . 2.6 crystal oscillator or external clock input the 2450 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. see programmable baud rate generator on page 8. t able 1: c hannel a and b s elect 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: inta and intb p ins o peration for t ransmitter t ransmitter r eceiver inta/b pin 0 = a byte in thr 1 = thr empty 0 = no data 1 = 1 byte
st16c2450 ? ? ? ? 2.97v to 5.5v duart rev. 4.0.0 8 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. 2.7 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 or external clock of up to 24 mhz. the 2450 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 3 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 4. t ypical oscillator connections divisor (decimal) = (xtal1 clock frequency) / (serial data rate x 16) c1 22-47 pf c2 22-47 pf y1 1.8432 mhz to 24 mhz r1 0-120 w (optional) r2 500 kw - 1 mw xtal1 xtal2
? ? ? ? st16c2450 rev. 4.0.0 2.97v to 5.5v duart 9 2.8 transmitter the transmitter section comprises of an 8-bit transmit shift register (tsr) and 1 byte fifo or 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). 2.8.1 transmit holding register (thr) - write only 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 3: 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 f igure 5. t ransmitter o peration 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
st16c2450 ? ? ? ? 2.97v to 5.5v duart rev. 4.0.0 10 2.9 receiver the receiver section contains an 8-bit receive shift register (rsr) and 1 byte fifo or receive holding register (rhr). the rsr uses the 16x clock 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 clock rate. 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. once the data is received, the error tags are immediately updated to reflect the status of the data byte in rhr register. rhr will generate a receive data ready interrupt upon receiving a character if ier bit-0 has been enabled. 2.9.1 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 1 byte receive fifo that is 11-bits wide, the 3 extra bits are for the 3 error tags to be reported in lsr register. after the rhr is read, lsr bits 2-4 willl immediately be updated to reflect the errors for the next character byte transferred from the rsr. f igure 6. r eceiver o peration 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
? ? ? ? st16c2450 rev. 4.0.0 2.97v to 5.5v duart 11 2.10 internal loopback the 2450 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 7 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 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. f igure 7. i nternal l oop b ack in c hannels 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 op2a#/op2b# vcc
st16c2450 ? ? ? ? 2.97v to 5.5v duart rev. 4.0.0 12 3.0 uart internal registers each of the uart channel in the 2450 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 16c450 compatible. the complete register set is shown on ta b l e 4 and ta b l e 5 . t able 4: 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 0 0 1 dlm - div latch high byte read/write lcr[7] = 1 0 0 1 ier - interrupt enable register read/write lcr[7] = 0 0 1 0 isr - interrupt status register reserved read-only write-only 0 1 1 lcr - line control register read/write 1 0 0 mcr - modem control register read/write 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
? ? ? ? st16c2450 rev. 4.0.0 2.97v to 5.5v duart 13 . 4.0 internal register descriptions 4.1 receive holding register (rhr) - read- only see receiver on page 10. 4.2 transmit holding register (thr) - write-only see transmitter on page 9. 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). t able 5: internal registers description 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 16c450 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 0 1 0 isr rd 0 0 0 0 int source bit-3 int source bit-2 int source bit-1 int source bit-0 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 rsrvd (op1#) rts# output control dtr# output control 1 0 1 lsr rd 0 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 0 0 1 dlm rd/wr bit-7 bit-6 bit-5 bit-4 bit-3 bit-2 bit-1 bit-0
st16c2450 ? ? ? ? 2.97v to 5.5v duart rev. 4.0.0 14 4.3.1 interrupt mode operation when the receive interrupt (ier bit-0 = 1) is enabled, the rhr interrupt (see isr bit-2) status will reflect the following: a. the receive data available interrupts are issued to the host when there is a character in the rhr. it will be cleared when the character has been read out of the rhr. b. 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 rhr is empty. 4.3.2 polled mode 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 the rhr. b. lsr bit-1 indicates an overrun error has occurred and that data in the rhr 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 thr is empty. e. lsr bit-6 indicates when both the thr and tsr are empty. ier[0]: rhr interrupt enable the receive data ready interrupt will be issued when rhr has a data character. 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. 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[7:4]: reserved 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 four 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 6 , shows the data values (bits 0-3) for the interrupt priority levels and the interrupt sources associated with each of these interrupt levels.
? ? ? ? st16c2450 rev. 4.0.0 2.97v to 5.5v duart 15 4.4.1 interrupt generation: lsr is by any of the lsr bits 1, 2, 3 and 4. rxrdy is by data byte received in rhr. txrdy is by thr empty. msr is by any of the msr bits 0, 1, 2 and 3. 4.4.2 interrupt clearing: lsr interrupt is cleared by a read to the lsr register. rxrdy interrupt is cleared by reading data out of 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. ] 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 ta b l e 6 ). isr[7:4]: reserved 4.5 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. t able 6: i nterrupt s ource and p riority l evel p riority l evel isr r egister s tatus b its s ource of interrupt b it -3 b it -2 b it -1 b it -0 1 0 1 1 0 lsr (receiver line status register) 2 0 1 0 0 rxrdy (received data ready) 3 0 0 1 0 txrdy (transmit ready) 4 0 0 0 0 msr (modem status register) - 0 0 0 1 none (default) bit-1 bit-0 w ord length 0 0 5 (default) 01 6 10 7 11 8
st16c2450 ? ? ? ? 2.97v to 5.5v duart rev. 4.0.0 16 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 7 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. 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. 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 t able 7: 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
? ? ? ? st16c2450 rev. 4.0.0 2.97v to 5.5v duart 17 lcr[7]: baud rate divisors (dll/dlm) enable logic 0 = data registers are selected (default). logic 1 = divisor latch registers are selected. 4.6 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 2450. 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 / 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. 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 7 . mcr[7:5]: reserved 4.7 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 . 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 there is data in the rhr. 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 rhr, therefore the data in the rhr is not corrupted by the error. an interrupt will be generated immediately if lsr interrupt is enabled (ier bit-2).
st16c2450 ? ? ? ? 2.97v to 5.5v duart rev. 4.0.0 18 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. 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). 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 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. 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. lsr[7]: reserved 4.8 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).
? ? ? ? st16c2450 rev. 4.0.0 2.97v to 5.5v duart 19 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. 4.9 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. 4.10 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 8. for more details.
st16c2450 ? ? ? ? 2.97v to 5.5v duart rev. 4.0.0 20 t able 8: 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 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 i/o signals reset state tx logic 1 op2# logic 1 rts# logic 1 dtr# logic 1 int three-state condition
? ? ? ? st16c2450 rev. 4.0.0 2.97v to 5.5v duart 21 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 (44-plcc) theta-ja = 50 o c/w, theta-jc = 21 o c/w thermal resistance (40-pdip) theta-ja = 50 o c/w, theta-jc = 22 o c/w electrical characteristics dc electrical characteristics u nless otherwise noted : 0 o to 70 o c (-40 o to +85 o c for industrial grade package ), v cc is 2.97v to 5.5v s ymbol p arameter t op m arking "a2 yyww" and newer u nits c onditions l imits 3.3v m in m ax l imits 5.0v m in m ax l imits 3.3v m in m ax l imits 5.0v m in m ax v ilck clock input low level -0.3 0.6 -0.5 0.6 -0.3 0.6 -0.5 0.6 v v ihck clock input high level 2.4 vcc 3.0 vcc 2.4 5.5 3.0 5.5 v v il input low voltage -0.3 0.8 -0.5 0.8 -0.3 0.8 -0.5 0.8 v v ih input high voltage 2.0 vcc 2.2 vcc 2.0 5.5 2.2 5.5 v v ol output low voltage 0.4 0.4 0.4 0.4 v v i ol = 6 ma i ol = 4 ma v oh output high voltage 2.0 2.4 2.0 2.4 v v i oh = -6 ma i oh = -1 ma i il input low leakage current 10 10 10 10 ua i ih input high leakage current 10 10 10 10 ua c in input pin capacitance5555pf i cc power supply current 1.3 3 1.3 3 ma
st16c2450 ? ? ? ? 2.97v to 5.5v duart rev. 4.0.0 22 ac electrical characteristics u nless otherwise noted : 0 o to 70 o c (-40 o to +85 o c for industrial grade package ), v cc is 2.97v to 5.5v, 70 p f load where applicable s ymbol p arameter l imits 3.3 m in m ax l imits 5.0 m in m ax u nit - crystal frequency 16 24 mhz clk external clock low/high time 25 21 ns osc external clock frequency 20 24 mhz t as address setup time 5 0 ns t ah address hold time 10 5 ns t cs chip select width 66 50 ns t rd ior# strobe width 35 25 ns t dy read cycle delay 40 30 ns t rdv data access time 35 25 ns t dd data disable time 0 25 0 15 ns t wr iow# strobe width 40 25 ns t dy write cycle delay 40 30 ns t ds data setup time 20 15 ns t dh data hold time 5 5 ns t wdo delay from iow# to output 50 40 ns t mod delay to set interrupt from modem input 40 35 ns t rsi delay to reset interrupt from ior# 40 35 ns t ssi delay from stop to set interrupt 1 1 bclk t int delay from initial int reset to transmit start 8 24 8 24 bclk t wri delay from iow# to reset interrupt 45 40 ns t rst reset pulse width 40 40 ns n baud rate divisor 1 2 16 -1 1 2 16 -1 - bclk baud clock 16x of data rate hz
? ? ? ? st16c2450 rev. 4.0.0 2.97v to 5.5v duart 23 f igure 8. c lock t iming f igure 9. m odem i nput /o utput t iming f or c hannels a & b 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
st16c2450 ? ? ? ? 2.97v to 5.5v duart rev. 4.0.0 24 f igure 10. d ata b us r ead t iming f igure 11. 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
? ? ? ? st16c2450 rev. 4.0.0 2.97v to 5.5v duart 25 f igure 12. i nterrupt t iming for c hannels a & b f igure 13. i nterrupt t iming for c hannels a & b rx ior# int d0:d7 start bit d0:d7 stop bit d0:d7 1 byte in rhr 1 byte in rhr 1 byte in rhr rxnfm t rsi t rsi t rsi t ssi (reading data out of rhr) t ssi t ssi tx iow# int* d0:d7 start bit d0:d7 stop bit d0:d7 txnonfifo t wri t wri t wri *int is cleared when the isr is read or when data is loaded into the thr. isr is read (loading data into thr) (unloading) ier[1] enabled t int isr is read isr is read t int t int
st16c2450 ? ? ? ? 2.97v to 5.5v duart rev. 4.0.0 26 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
? ? ? ? st16c2450 rev. 4.0.0 2.97v to 5.5v duart 27 package dimensions (44 pin plcc) note: the control dimension is the millimeter column inches millimeters symbol min max min max a 0.165 0.180 4.19 4.57 a 1 0.090 0.120 2.29 3.05 a 2 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 d 1 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
st16c2450 ? ? ? ? 2.97v to 5.5v duart rev. 4.0.0 28 package dimensions (40 pin pdip) note: the control dimension is the millimeter column inches millimeters symbol min max min max a 0.160 0.250 4.06 6.35 a1 0.015 0.070 0.38 1.78 a2 0.125 0.195 3.18 4.95 b 0.014 0.024 0.36 0.56 b1 0.030 0.070 0.76 1.78 c 0.008 0.014 0.20 0.38 d 1.98 2.095 50.29 53.21 e 0.600 0.625 15.24 15.88 e1 0.485 0.580 12.32 14.73 e 0.100 bsc 2.54 bsc ea 0.600 bsc 15.24 bsc eb 0.600 0.700 15.24 17.78 l 0.115 0.200 2.92 5.08 a 0 15 0 15 40 1 21 20 d e a 1 e 1 e a l seating plane a 2 a b 1 b c e b e a
? ? ? ? st16c2450 rev. 4.0.0 2.97v to 5.5v duart 29 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 september 2003 4.0.0 changed to standard style, single-column format. clarified timing diagrams. added device status to ordering information. devices with top markings of "a2 yyww" and newer have 5v tolerant inputs. devices with top markings of "cc yyww" and older do not have 5v tolerant inputs.

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