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tl16c554, tl16c554i asynchronous communications element slls165d january 1994 revised july 1998 1 post office box 655303 ? dallas, texas 75265 integrated asynchronous communications element consists of four improved tl16c550 aces plus steering logic in fifo mode, each ace transmitter and receiver is buffered with 16-byte fifo to reduce the number of interrupts to cpu in tl16c450 mode, hold and shift registers eliminate need for precise synchronization between the cpu and serial data up to 16-mhz clock rate for up to 1-mbaud operation programmable baud rate generators which allow division of any input reference clock by 1 to (2 16 1) and generate an internal 16 clock adds or deletes standard asynchronous communication bits (start, stop, and parity) to or from the serial data stream independently controlled transmit, receive, line status, and data set interrupts fully programmable serial interface characteristics: 5-, 6-, 7-, or 8-bit characters even-, odd-, or no-parity bit 1-, 1 1/2-, or 2-stop bit generation baud generation (dc to 1-mbit per second) false start bit detection complete status reporting capabilities line break generation and detection internal diagnostic capabilities: loopback controls for communications link fault isolation break, parity, overrun, framing error simulation fully prioritized interrupt system controls modem control functions (cts , rts , dsr , dtr , ri , and dcd ) 3-state outputs provide ttl drive capabilities for bidirectional data bus and control bus description the tl16c554 and the tl16c554i are enhanced quadruple versions of the tl16c550b asynchronous communications element (ace). each channel performs serial-to-parallel conversion on data characters received from peripheral devices or modems and parallel-to-serial conversion on data characters transmitted by the cpu. the complete status of each channel of the quadruple ace can be read at any time during functional operation by the cpu. the information obtained includes the type and condition of the operation performed and any error conditions encountered. the tl16c554 and the tl16c554i quadruple ace can be placed in an alternate fifo mode, which activates the internal fifos to allow 16 bytes (plus three bits of error data per byte in the receiver fifo) to be stored in both receive and transmit modes. to minimize system overhead and maximize system efficiency, all logic is on the chip. two terminal functions allow signaling of direct memory access (dma) transfers. each ace includes a programmable baud rate generator that can divide the timing reference clock input by a divisor between 1 and (2 16 1). the tl16c554 and the tl16c554i are available in a 68-pin plastic-leaded chip-carrier (plcc) fn package and in an 80-pin (tqfp) pn package. please be aware that an important notice concerning availability, standard warranty, and use in critical applications of texas instruments semiconductor products and disclaimers thereto appears at the end of this data sheet. production data information is current as of publication date. products conform to specifications per the terms of texas instruments standard warranty. production processing does not necessarily include testing of all parameters. copyright ? 1998, texas instruments incorporated
tl16c554, tl16c554i asynchronous communications element slls165d january 1994 revised july 1998 2 post office box 655303 ? dallas, texas 75265 28 29 dsrd ctsd dtrd gnd rtsd intd csd txd ior txc csc intc rtsc v cc dtrc ctsc dsrc 60 59 58 57 56 55 54 53 52 51 50 49 48 47 46 45 44 30 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 dsra ctsa dtra v cc rtsa inta csa txa iow txb csb intb rtsb gnd dtrb ctsb dsrb 31 32 33 34 fn package (top view) d2 d1 87 6 54 93 rxa gnd d7 d6 d5 d4 d3 xtal2 reset rxrdy txrdy rxb nc a2 a1 a0 xtal1 16867 2 35 36 37 38 39 66 65 27 dcdb d0 intn 64 63 62 61 40 41 42 43 gnd rxc ric dcdc rxd rid dcdd dcda ria v cc rib v cc nc no internal connection
tl16c554, tl16c554i asynchronous communications element slls165d january 1994 revised july 1998 3 post office box 655303 ? dallas, texas 75265 23 nc dsrb ctsb dtrb gnd rtsb intb csb txb iow nc txa csa inta rtsa v cc dtra ctsa dsra nc 40 39 38 37 36 35 34 33 32 31 30 29 28 27 26 25 24 23 22 21 4 61 62 63 64 65 66 67 68 69 70 71 72 73 74 75 76 77 78 79 80 nc dsrc ctsc dtrc v cc rtsc intc csc txc ior nc txd csd intd rtsd gnd dtrd ctsd dsrd nc 5678 pn package (top view) xtal1 59 58 57 56 55 60 54 ric rxc gnd txrdy rxrdy reset nc d3 d5 rid rxd nc intn d0 d1 d2 52 51 50 53 9 10 11 12 13 49 48 1 nc a0 47 46 45 44 14 15 16 17 d6 d7 gnd rxa a1 a2 xtal2 rxb nc dcdc ria dcda 18 19 20 rib dcdb 43 42 41 v cc nc nc cc v dcdd d4 nc nc no internal connection
tl16c554, tl16c554i asynchronous communications element slls165d january 1994 revised july 1998 4 post office box 655303 ? dallas, texas 75265 functional block diagram 2 tl16c550b circuitry tl16c550b circuitry tl16c550b circuitry tl16c550b circuitry receive control logic transmit control logic modem control logic control logic data bus clock circuit rxx txx ctsx rtsx dsrx dtrx rix dcdx d7 d0 a2 a0 csx ior , iow reset xtal1 xtal2 intx txrdy , rxrdy interrupt logic 8 2 for tl16c550 circuitry, refer to the tl16c550b data sheet. terminal functions terminal name fn no. pn no. i/o description a0 a1 a2 34 33 32 48 47 46 i register select terminals. a0, a1, and a2 are three inputs used during read and write operations to select the ace register to read or write. csa , csb , csc , csd 16, 20, 50, 54 28, 33, 68, 73 i chip select. each chip select (csx ) enables read and write operations to its respective channel. ctsa , ctsb , ctsc , ctsd 11, 25, 45, 59 23, 38, 63, 78 i clear to send. ctsx is a modem status signal. its condition can be checked by reading bit 4 (cts) of the modem status register. cts has no affect on the transmit or receive operation. d7 d0 66 68 15 1511, 97 i/o data bus. eight data lines with 3-state outputs provide a bidirectional path for data, control, and status information between the tl16c554 and the cpu. d0 is the least significant bit (lsb). dcda , dcdb , dcdc , dcdd 9, 27, 43, 61 19,42, 59, 2 i data carrier detect. a low on dcdx indicates the carrier has been detected by the modem. the condition of this signal is checked by reading bit 7 of the modem status register. dsra , dsrb , dsrc , dsrd 10, 26, 44, 60 22, 39, 62, 79 i data set ready. dsrx is a modem status signal. its condition can be checked by reading bit 5 (dsr) of the modem status register. dsr has no affect on the transmit or receive operation. dtra , dtrb , dtrc , dtrd 12, 24, 46, 58 24, 37, 64, 77 o data terminal ready. dtrx is an output that indicates to a modem or data set that the ace is ready to establish communications. it is placed in the active state by setting the dtr bit of the modem control register. dtrx is placed in the inactive state (high) either as a result of the master reset during loop mode operation or clearing bit 0 (dtr ) of the modem control register. gnd 6, 23, 40, 57 16, 36, 56, 76 signal and power ground intn 65 6 i interrupt normal. intn operates in conjunction with bit 3 of the modem status register and affects operation of the interrupts (inta, intb, intc, and intd) for the four universal asynchronous receiver/transceivers (uarts) per the following table. intn operation of interrupts brought low or allowed to float interrupts are enabled according to the state of out2 (mcr bit 3). when the mcr bit 3 is cleared, the 3-state interrupt output of that uart is in the high-impedance state. when the mcr bit 3 is set, the interrupt output of the uart is enabled. brought high interrupts are always enabled, overriding the out2 enables.
tl16c554, tl16c554i asynchronous communications element slls165d january 1994 revised july 1998 5 post office box 655303 ? dallas, texas 75265 terminal functions (continued) terminal name fn no. pn no. i/o description inta, intb, intc, intd 15, 21, 49, 55 27, 34, 67, 74 o external interrupt output. the intx outputs go high (when enabled by the interrupt register) and inform the cpu that the ace has an interrupt to be serviced. four conditions that cause an interrupt to be issued are: a receiver error, receiver data available or timeout (fifo mode only), transmitter holding register empty, and an enabled modem status interrupt. the interrupt is disabled when it is serviced or as the result of a master reset. ior 52 70 i read strobe. a low level on ior transfers the contents of the tl16c554 data bus to the external cpu bus. iow 18 31 i write strobe. iow allows the cpu to write into the selected address by the address register. reset 37 53 i master reset. when active, reset clears most ace registers and sets the state of various signals. the transmitter output and the receiver input is disabled during reset time. ria , rib , ric , rid 8, 28, 42, 62 18, 43, 58, 3 i ring detect indicator. a low on rix indicates the modem has received a ring signal from the telephone line. the condition of this signal can be checked by reading bit 6 of the modem status register. rtsa , rtsb , rtsc , rtsd 14, 22, 48, 56 26, 35, 66, 75 o request to send. when active, rtsx informs the modem or data set that the ace is ready to receive data. writing a 1 in the modem control register sets this bit to a low state. after reset, this terminal is set high. these terminals have no affect on the transmit or receive operation. rxa, rxb rxc, rxd 7, 29, 41, 63 17, 44, 57, 4 i serial input. rxx is a serial data input from a connected communications device. during loopback mode, the rxx input is disabled from external connection and connected to the txx output internally. rxrdy 38 54 o receive ready. rxrdy goes low when the receive fifo is full. it can be used as a single transfer or multitransfer. txa, txb txc, txd 17, 19, 51, 53 29, 32, 69, 72 o transmit outputs. txx is a composite serial data output that is connected to a communications device. txa, txb, txc, and txd are set to the marking (high) state as a result of reset. txrdy 39 55 o transmit ready. txrdy goes low when the transmit fifo is full. it can be used as a single transfer or multitransfer function. vcc 13, 30, 47, 64 5, 25, 45, 65 power supply xtal1 35 50 i crystal input 1 or external clock input. a crystal can be connected to xtal1 and xtal2 to utilize the internal oscillator circuit. an external clock can be connected to drive the internal clock circuits. xtal2 36 51 o crystal output 2 or buffered clock output (see xtal1). absolute maximum ratings over free-air temperature range (unless otherwise noted) 2 supply voltage range, v cc (see note 1) 0.5 v to 7 v . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . input voltage range at any input, v i 0.5 v to 7 v . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . output voltage range, v o 0.5 v to v cc + 3 v . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . continuous total power dissipation at (or below) 70 c 500 mw . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . operating free-air temperature range, t a : tl16c554 0 c to 70 c . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . tl16c554i 40 c to 85 c . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . storage temperature range, t stg 65 c to 150 c . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2 stresses beyond those listed under aabsolute maximum ratingso may cause permanent damage to the device. these are stress rating s only, and functional operation of the device at these or any other conditions beyond those indicated under arecommended operating conditi onso is not implied. exposure to absolute-maximum-rated conditions for extended periods may affect device reliability. note 1: all voltage levels are with respect to gnd.
tl16c554, tl16c554i asynchronous communications element slls165d january 1994 revised july 1998 6 post office box 655303 ? dallas, texas 75265 recommended operating conditions min nom max unit supply voltage, v cc 4.75 5 5.25 v clock high-level input voltage at xtal1, v ih(clk) 2 v cc v clock low-level input voltage at xtal1, v il(clk) 0.5 0.8 v high-level input voltage, v ih 2 v cc v low-level input voltage, v il 0.5 0.8 v clock frequency, f clock 16 mhz o p erating free-air tem p erature t a tl16c554 0 70 c o erating free - air tem erature , t a tl16c554i 40 85 c electrical characteristics over recommended ranges of operating free-air temperature and supply voltage (unless otherwise noted) parameter test conditions min typ 2 max unit v oh 3 high-level output voltage i oh = 1 ma 2.4 v v ol 3 low-level output voltage i ol = 1.6 ma 0.4 v i ikg input leakage current v cc = 5.25 v, gnd = 0, v i = 0 to 5.25 v, all other terminals floating 10 m a i oz high-impedance output current v cc = 5.25 v, gnd = 0, v o = 0 to 5.25 v, chip selected in write mode or chip deselected 20 m a i cc supply current v cc = 5.25 v, t a = 25 c, rx, dsr , dcd , cts, and ri at 2 v, all other inputs at 0.8 v, xtal1 at 4 mhz, no load on outputs, baud rate = 50 kilobits per second 50 ma c i(xtal1) clock input capacitance 15 20 pf c o(xtal2) clock output capacitance v cc = 0, v ss = 0, all other terminals grounded f=1mhz 20 30 pf c i input capacitance all other terminals grounded , f = 1 mhz , t a = 25 c 6 10 pf c o output capacitance t a 25 c 10 20 pf 2 all typical values are at v cc = 5 v, t a = 25 c. 3 these parameters apply for all outputs except xtal2. clock timing requirements over recommended ranges of operating free-air temperature and supply voltage (see figure 1) min max unit t w1 pulse duration, clock high (external clock) 31 ns t w2 pulse duration, clock low (external clock) 31 ns t w3 pulse duration, reset 1000 ns
tl16c554, tl16c554i asynchronous communications element slls165d january 1994 revised july 1998 7 post office box 655303 ? dallas, texas 75265 read cycle timing requirements over recommended ranges of operating free-air temperature and supply voltage (see figure 4) min max unit t w4 pulse duration, ior low 75 ns t su1 setup time, csx valid before ior low (see note 2) 10 ns t su2 setup time, a2 a0 valid before ior low (see note 2) 15 ns t h1 hold time, a2 a0 valid after ior high (see note 2) 0 ns t h2 hold time, csx valid after ior high (see note 2) 0 ns t d1 delay time, t su2 + t w4 + t d2 (see note 3) 140 ns t d2 delay time, ior high to ior or iow low 50 ns notes: 2. the internal address strobe is always active. 3. in the fifo mode, t d1 = 425 ns (min) between reads of the receiver fifo and the status registers (interrupt identification register and line status register). write cycle timing requirements over recommended ranges of operating free-air temperature and supply voltage (see figure 5) min max unit t w5 pulse duration, iow 50 ns t su3 setup time, csx valid before iow (see note 2) 10 ns t su4 setup time, a2 a0 valid before iow (see note 2) 15 ns t su5 setup time, d7 d0 valid before iow 10 ns t h3 hold time, a2 a0 valid after iow (see note 2) 5 ns t h4 hold time, csx valid after iow (see note 2) 5 ns t h5 hold time, d7 d0 valid after iow 25 ns t d3 delay time, t su4 + t w5 + t d4 120 ns t d4 delay time, iow to iow or ior 55 ns note 2: the internal address strobe is always active. read cycle switching characteristics over recommended ranges of operating free-air temperature and supply voltage, c l = 100 pf (see note 4 and figure 4) parameter min max unit t en enable time, ior to d7 d0 valid 30 ns t dis disable time, ior to d7 d0 released 0 20 ns note 4: v ol and v oh (and the external loading) determine the charge and discharge time.
tl16c554, tl16c554i asynchronous communications element slls165d january 1994 revised july 1998 8 post office box 655303 ? dallas, texas 75265 transmitter switching characteristics over recommended ranges of operating free-air temperature and supply voltage (see figures 6, 7, and 8) parameter test conditions min max unit t d5 delay time, intx to txx at start 8 24 rclk cycles t d6 delay time, txx at start to intx see note 5 8 8 rclk cycles t d7 delay time, iow high or low (wr thr) to intx see note 5 16 32 rclk cycles t d8 delay time, txx at start to txrdy c l = 100 pf 8 rclk cycles t pd1 propagation delay time, iow (wr thr) to intx c l = 100 pf 35 ns t pd2 propagation delay time, ior (rd iir) to intx c l = 100 pf 30 ns t pd3 propagation delay time, iow (wr thr) to txrdy c l = 100 pf 50 ns note 5: if the transmitter interrupt delay is active, this delay is lengthened by one character time minus the last stop bit tim e. receiver switching characteristics over recommended ranges of operating free-air temperature and supply voltage (see figures 9 through 13) parameter test conditions min max unit t d9 delay time, stop bit to intx or stop bit to rxrdy or read rbr to set interrupt see note 6 1 rclk cycle t pd4 propagation delay time, read rbr/lsr to intx /lsr interrupt c l = 100 pf, see note 7 40 ns t pd5 propagation delay time, ior rclk to rxrdy see note 7 30 ns notes: 6. the receiver data available indicator, the overrun error indicator, the trigger level interrupts, and the active rxrdy indicator are delayed three rclk (internal receiver timing clock) cycles in the fifo mode (fcr0 = 1). after the first byte has been received, status indicators (pe, fe, bi) are delayed three rclk cycles. these indicators are updated immediately for any further bytes received after ior goes active for a read from the rbr register. there are eight rclk cycle delays for trigger change level interrupts. 7. rclk is an internal signal derived from divisor latch lsb (dll) and divisor latch msb (dlm) divisor latches. modem control switching characteristics over recommended ranges of operating free-air temperature and supply voltage, c l = 100 pf (see figure 14) parameter min max unit t pd6 propagation delay time, iow (wr mcr) to rtsx, dtrx 50 ns t pd7 propagation delay time, modem input ctsx, dsrx , and dcdx to intx 30 ns t pd8 propagation delay time, ior (rd msr) to interrupt 35 ns t pd9 propagation delay time, rix to intx 30 ns
tl16c554, tl16c554i asynchronous communications element slls165d january 1994 revised july 1998 9 post office box 655303 ? dallas, texas 75265 parameter measurement information clock (xtal1) f clock = 16 mhz max t w2 t w1 0.8 v 2 v t w3 reset 2 v 2 v 0.8 v 0.8 v (a) clock input voltage waveform (b) reset voltage waveform figure 1. clock input and reset voltage waveforms 82 pf (see note a) 680 w 2.54 v device under test tl16c554 note a: this includes scope and jig capacitance. figure 2. output load circuit 9-pin d connector serial channel 1 buffers serial channel 2 buffers serial channel 3 buffers serial channel 4 buffers 9-pin d connector 9-pin d connector 9-pin d connector data bus address bus control bus quadruple ace tl16c554 figure 3. basic test configuration
tl16c554, tl16c554i asynchronous communications element slls165d january 1994 revised july 1998 10 post office box 655303 ? dallas, texas 75265 parameter measurement information t w4 t d2 active valid a2, a1, a0 valid valid data ior iow d7 d0 t h1 t h2 t su1 t su2 active t d1 t en t dis or active csx 50% 50% 50% 50% 50% 50% 50% 50% figure 4. read cycle timing waveforms valid a2, a1, a0 valid valid data ior iow d7 d0 t su3 t su4 t w5 t d3 t h4 t d4 t su5 t h5 active or active t h3 active csx 50% 50% 50% 50% 50% 50% 50% 50% figure 5. write cycle timing waveforms
tl16c554, tl16c554i asynchronous communications element slls165d january 1994 revised july 1998 11 post office box 655303 ? dallas, texas 75265 parameter measurement information start ior (rd iir) iow ( wr thr) t pd1 t d7 t d5 t d6 t pd2 start data (5 8) parity stop (1 2) t pd1 txx intx 50% 50% 50% 50% 50% 50% 50% 50% 50% 50% 50% figure 6. transmitter timing waveforms byte #1 iow (wr thr) data t d8 start parity stop t pd3 txrdy txx fifo empty 50% 50% 50% 50% figure 7. transmitter ready mode 0 timing waveforms iow (wr thr) txrdy byte #16 data t d8 start parity stop t pd3 start fifo full txx 50% 50% 50% 50% figure 8. transmitter ready mode 1 timing waveforms
tl16c554, tl16c554i asynchronous communications element slls165d january 1994 revised july 1998 12 post office box 655303 ? dallas, texas 75265 parameter measurement information t pd4 parity stop start data bits (5 8) tl16c450 mode: sample clock sin (receiver input data) intx (data ready or rcvr err) ior t d9 active 50% 50% 50% figure 9. receiver timing waveforms start data bits (5 8) parity stop sample clock t d9 t pd4 intx (trigger interrupt) (fcr6, 7 = 0, 0) (fifo at or above trigger level) (fifo below trigger level) active ior (rd rbr) ior (rd lsr) t pd4 active rxx lsr interrupt 50% 50% 50% 50% 50% 50% figure 10. receiver fifo first byte (sets rdr) waveforms
tl16c554, tl16c554i asynchronous communications element slls165d january 1994 revised july 1998 13 post office box 655303 ? dallas, texas 75265 parameter measurement information stop t d9 (see note a) t pd4 top byte of fifo t pd4 t d9 active active sample clock intx (time-out or trigger level) interrupt ior (rd rbr) ior (rd lsr) previous byte read from fifo active (fifo at or above trigger level) (fifo below trigger level) rxx intx interrupt 50% 50% 50% 50% 50% 50% 50% note a: this is the reading of the last byte in the fifo. figure 11. receiver fifo after first byte (after rdr set) waveforms
rxx 50% 50% 50% notes: a. this is the reading of the last byte in the fifo. b. if fcr0 = 1, then t d9 = 3 rclk cycles. for a time-out interrupt, t d9 = 8 rclk cycles. figure 12. receiver ready mode 0 timing waveforms
tl16c554, tl16c554i asynchronous communications element slls165d january 1994 revised july 1998 14 post office box 655303 ? dallas, texas 75265 parameter measurement information !" ! ! ! ! !

! #! !! ! ! " 50% 50% 50% notes: a. this is the reading of the last byte in the fifo. b. if fcr0 = 1, t d9 = 3 rclk cycles. for a trigger change level interrupt, t d9 = 8 rclk. figure 13. receiver ready mode 1 timing waveforms t pd6 t pd6 t pd7 t pd7 t pd8 t pd9 iow (wr mcr) ior (rd msr) rtsx, dtrx ctsx , dsrx , dcdx rix intx 50% 50% 50% 50% 50% 50% 50% 50% 50% 50% 50% 50% figure 14. modem control timing waveforms
tl16c554, tl16c554i asynchronous communications element slls165d january 1994 revised july 1998 15 post office box 655303 ? dallas, texas 75265 principles of operation three types of information are stored in the internal registers used in the ace: control, status, and data. mnemonic abbreviations for the registers are shown in table 1. table 2 defines the address location of each register and whether it is read only, write only, or read writable. table 1. internal register mnemonic abbreviations control mnemonic status mnemonic data mnemonic line control register lcr line status register lsr receiver buffer register rbr fifo control register fcr modem status register msr transmitter holding register thr modem control register mcr divisor latch lsb dll divisor latch msb dlm interrupt enable register ier table 2. register selection 2 dlab 3 a2 a1 a0 read mode write mode 0 0 0 0 receiver buffer register transmitter holding register 0 001 interrupt enable register x 0 1 0 interrupt identification register fifo control register x 011 line control register x 100 modem control register x 1 0 1 line status register x 1 1 0 modem status register x 1 1 1 scratchpad register scratchpad register 1 000 lsb divisor latch 1 0 0 1 msb divisor latch x = irrelevant, 0 = low level, 1 = high level 2 the serial channel is accessed when either csa or csd is low. 3 dlab is the divisor latch access bit and bit 7 in the lcr. a2 a0 are device terminals. individual bits within the registers with the bit number in parenthesis are referred to by the register mnemonic. for example, lcr7 refers to line control register bit 7. the transmitter buffer register and receiver buffer register are data registers that hold from five to eight bits of data. if less than eight data bits are transmitted, data is right justified to the lsb. bit 0 of a data word is always the first serial data bit received and transmitted. the ace data registers are double buffered (tl16450 mode) or fifo buffered (fifo mode) so that read and write operations can be performed when the ace is performing the parallel-to-serial or serial-to-parallel conversion.
tl16c554, tl16c554i asynchronous communications element slls165d january 1994 revised july 1998 16 post office box 655303 ? dallas, texas 75265 principles of operation accessible registers the system programmer, using the cpu, has access to and control over any of the ace registers that are summarized in table 1. these registers control ace operations, receive data, and transmit data. descriptions of these registers follow table 3. table 3. summary of accessible registers address register register address address mnemonic bit 7 bit 6 bit 5 bit 4 bit 3 bit 2 bit 1 bit 0 0 rbr (read only) data bit 7 (msb) data bit 6 data bit 5 data bit 4 data bit 3 data bit 2 data bit 1 data bit 0 (lsb) 0 thr (write only) data bit 7 data bit 6 data bit 5 data bit 4 data bit 3 data bit 2 data bit 1 data bit 0 0 2 dll bit 7 bit 6 bit 5 bit 4 bit 3 bit 2 bit 1 bit 0 1 2 dlm bit 15 bit 14 bit 13 bit 12 bit 11 bit 10 bit 9 bit 8 1 ier 0 0 0 0 (edssi) enable modem status interrupt (erlsi) enable receiver line status interrupt (etbei) enable transmitter holding register empty interrupt (erbi) enable received data available interrupt 2 fcr (write only) receiver trigger (msb) receiver trigger (lsb) reserved reserved dma mode select transmit fifo reset receiver fifo reset fifo enable 2 iir (read only) fifos enabled 3 fifos enabled 3 0 0 interrupt id bit (3) 3 interrupt id bit (2) interrupt id bit (1) 0 if interrupt pending 3 lcr (dlab) divisor latch access bit set break stick parity (eps) even parity select (pen) parity enable (stb) number of stop bits (wlsb1) word length select bit 1 (wlsb0) word length select bit 0 4 mcr 0 0 0 loop out2 enable external interrupt (int) reserved (rts) request to send (dtr) data terminal ready 5 lsr error in receiver fifo 3 (temt) transmitter registers empty (thre) transmitter holding register empty (bi) break interrupt (fe) framing error (pe) parity error (oe) overrun error (dr) data ready 6 msr (dcd) data carrier detect (ri) ring indicator (dsr) data set ready (cts) clear to send ( d dcd) delta data carrier detect (teri) trailing edge ring indicator ( d dsr) delta data set ready ( d cts) delta clear to send 7 scr bit 7 bit 6 bit 5 bit 4 bit 3 bit 2 bit 1 bit 0 2 dlab = 1 3 these bits are always 0 when fifos are disabled.
tl16c554, tl16c554i asynchronous communications element slls165d january 1994 revised july 1998 17 post office box 655303 ? dallas, texas 75265 principles of operation fifo control register (fcr) the fcr is a write-only register at the same location as the iir. it enables the fifos, sets the trigger level of the receiver fifo, and selects the type of dma signalling. bit 0: fcr0 enables the transmit and receiver fifos. all bytes in both fifos can be cleared by clearing fcr0. data is cleared automatically from the fifos when changing from the fifo mode to the tl16c450 mode (see fcr bit 0) and vice versa. programming of other fcr bits is enabled by setting fcr0. bit 1: when set, fcr1 clears all bytes in the receiver fifo and resets its counter. this does not clear the shift register. bit 2: when set, fcr2 clears all bytes in the transmit fifo and resets the counter. this does not clear the shift register. bit 3: when set, fcr3 changes rxrdy and txrdy from mode 0 to mode 1 if fcr0 is set. bits 4 and 5: fcr4 and fcr5 are reserved for future use. bits 6 and 7: fcr6 and fcr7 set the trigger level for the receiver fifo interrupt (see table 4). table 4. receiver fifo trigger level bit receiver fifo 7 6 receiver fifo trigger level (bytes) 0 0 01 0 1 04 1 0 08 1 1 14 fifo interrupt mode operation the following receiver status occurs when the receiver fifo and receiver interrupts are enabled. 1. lsr0 is set when a character is transferred from the shift register to the receiver fifo. when the fifo is empty, it is reset. 2. iir = 06 receiver line status interrupt has higher priority than the receive data available interrupt iir = 04. 3. receive data available interrupt is issued to the cpu when the programmed trigger level is reached by the fifo. as soon as the fifo drops below its programmed trigger level, it is cleared. 4. iir = 04 (receive data available indicator) also occurs when the fifo reaches its trigger level. it is cleared when the fifo drops below the programmed trigger level. the following receiver fifo character time-out status occurs when receiver fifo and receiver interrupts are enabled.
tl16c554, tl16c554i asynchronous communications element slls165d january 1994 revised july 1998 18 post office box 655303 ? dallas, texas 75265 principles of operation fifo interrupt mode operation (continued) 1. when the following conditions exist, a fifo character time-out interrupt occurs: a. minimum of one character in fifo b. last received serial character is longer than four continuous previous character times ago. (if two stop bits are programmed, the second one is included in the time delay.) c. the last cpu of the fifo read is more than four continuous character times earlier. at 300 baud and 12-bit characters, the fifo time-out interrupt causes a latency of 160 ms maximum from received character to interrupt issued. 2. by using the xtal1 input for a clock signal, the character times can be calculated. the delay is proportional to the baud rate. 3. the time-out timer is reset after the cpu reads the receiver fifo or after a new character is received. this occurs when there has been no time-out interrupt. 4. a time-out interrupt is cleared and the timer is reset when the cpu reads a character from the receiver fifo. transmit interrupts occurs as follows when the transmitter and transmit fifo interrupts are enabled (fcr0 = 1, ier = 1). 1. when the transmitter fifo is empty, the transmitter holding register interrupt (iir = 02) occurs. the interrupt is cleared when the transmitter holding register is written to or the iir is read. one to sixteen characters can be written to the transmit fifo when servicing this interrupt. 2. the transmitter fifo empty indicators are delayed one character time minus the last stop bit time whenever the following occurs: thre = 1, and there has not been a minimum of two bytes at the same time in transmit fifo since the last thre = 1. the first transmitter interrupt after changing fcr0 is immediate, however, assuming it is enabled. receiver fifo trigger level and character time-out interrupts have the same priority as the receive data available interrupt. the transmitter holding register empty interrupt has the same priority as the transmitter fifo empty interrupt. fifo polled mode operation clearing ier0, ier1, ier2, ier3, or all to zero with fcr0 = 1 puts the ace into the fifo polled mode. receiver and transmitter are controlled separately. either or both can be in the polled mode. in the fifo polled mode, there is no time-out condition indicated or trigger level reached. however, the receiver and transmit fifos still have the capability of holding characters. the lsr must be read to determine the ace status. interrupt enable register (ier) the ier independently enables the four serial channel interrupt sources that activate the interrupt (inta, b, c, d) output. all interrupts are disabled by clearing ier0 ier3 of the ier. interrupts are enabled by setting the appropriate bits of the ier. disabling the interrupt system inhibits the iir and the active (high) interrupt output. all other system functions operate in their normal manner, including the setting of the lsr and msr. the contents of the ier are shown in table 3 and described in the following bulleted list:
tl16c554, tl16c554i asynchronous communications element slls165d january 1994 revised july 1998 19 post office box 655303 ? dallas, texas 75265 principles of operation interrupt enable register (ier) (continued) bit 0: when ier0 is set, ier0 enables the received data available interrupt and the timeout interrupts in the fifo mode. bit 1: when ier1 is set, the transmitter holding register empty interrupt is enabled. bit 2: when ier2 is set, the receiver line status interrupt is enabled. bit 3: when ier3 is set, the modem status interrupt is enabled. bits 4 7: ier4 ier7. these four bits of the ier are cleared. interrupt identification register (iir) in order to minimize software overhead during data character transfers, the serial channel prioritizes interrupts into four levels. the four levels of interrupt conditions are as follows: priority 1 receiver line status (highest priority) priority 2 receiver data ready or receiver character timeout priority 3 transmitter holding register empty priority 4 modem status (lowest priority) information indicating that a prioritized interrupt is pending and the type of interrupt that is stored in the iir. the iir indicates the highest priority interrupt pending. the contents of the iir are indicated in table 5. table 5. interrupt control functions interrupt identification register interrupt set and reset functions bit 3 bit 2 bit 1 bit 0 priority level interrupt type interrupt source interrupt reset control 0 0 0 1 e none none e 0 1 1 0 first receiver line status oe, pe, fe, or bi lsr read 0 1 0 0 second received data available receiver data available or trigger level reached rbr read until fifo drops below the trigger level 1 1 0 0 second character time-out indicator no characters have been removed from or input to the receiver fifo during the last four character times, and there is at least one character in it during this time. rbr read 0 0 1 0 third thre thre iir read if thre is the interrupt source or thr write 0 0 0 0 fourth modem status cts , dsr , ri , or dcd
tl16c554, tl16c554i asynchronous communications element slls165d january 1994 revised july 1998 20 post office box 655303 ? dallas, texas 75265 principles of operation interrupt identification register (iir) (continued) bit 0: iir0 indicates whether an interrupt is pending. when iir0 is cleared, an interrupt is pending. bits 1 and 2: iir1 and iir2 identify the highest priority interrupt pending as indicated in table 5. bit 3: iir3 is always cleared when in the tl16c450 mode. this bit is set along with bit 2 when in the fifo mode and a trigger change level interrupt is pending. bits 4 and 5: iir4 and iir5 are always cleared. bits 6 and 7: iir6 and iir7 are set when fcr0 = 1. line control register (lcr) the format of the data character is controlled by the lcr. the lcr may be read. its contents are described in the following bulleted list and shown in figure 15. bits 0 and 1: lcr0 and lcr1 are word length select bits. these bits program the number of bits in each serial character and are shown in figure 15. bit 2: lcr2 is the stop bit select bit. this bit specifies the number of stop bits in each transmitted character. the receiver always checks for one stop bit. bit 3: lcr3 is the parity enable bit. when lcr3 is set, a parity bit between the last data word bit and stop bit is generated and checked. bit 4: lcr4 is the even parity select bit. when this bit is set and parity is enabled (lcr3 is set), even parity is selected. when this bit is cleared and parity is enabled, odd parity is selected. bit 5: lcr5 is the stick parity bit. when parity is enabled (lcr3 is set) and this bit is set, the transmission and reception of a parity bit is placed in the opposite state from the value of lcr4. this forces parity to a known state and allows the receiver to check the parity bit in a known state. bit 6: lcr6 is a break control bit. when this bit is set, the serial outputs txx are forced to the spacing state (low). the break control bit acts only on the serial output and does not affect the transmitter logic. if the following sequence is used, no invalid characters are transmitted because of the break. step 1. load a zero byte in response to the transmitter holding register empty (thre) status indicator. step 2. set the break in response to the next thre status indicator. step 3. wait for the transmitter to be idle when transmitter empty status signal is set (temt = 1); then clear the break when the normal transmission has to be restored. bit 7: lcr7 is the divisor latch access bit (dlab) bit. this bit must be set to access the divisor latches dll and dlm of the baud rate generator during a read or write operation. lcr7 must be cleared to access the receiver buffer register, the transmitter holding register, or the interrupt enable register.
tl16c554, tl16c554i asynchronous communications element slls165d january 1994 revised july 1998 21 post office box 655303 ? dallas, texas 75265 principles of operation line control register (lcr) (continued) word length select 0 0 = 5 data bits 0 1 = 6 data bits 1 0 = 7 data bits 1 1 = 8 data bits line control register lcr 7 lcr 6 lcr 5 lcr 4 lcr 3 lcr 2 lcr 1 lcr 0 stop bit select 0 = 1 stop bit 1 = 1.5 stop bits if 5 data bits selected 2 stop bits if 6, 7, 8 data bits selected parity enable 0 = parity disabled 1 = parity enabled even parity select 0 = odd parity 1 = even parity stick parity 0 = stick parity disabled 1 = stick parity enabled break control 0 = break disabled 1 = break enabled divisor latch access bit 0 = access receiver buffer 1 = access divisor latches figure 15. line control register contents line status register (lsr) the lsr is a single register that provides status indicators. the lsr shown in table 6 is described in the following bulleted list: bit 0: lsr0 is the data ready (dr) bit. data ready is set when an incoming character is received and transferred into the receiver buffer register or the fifo. lsr0 is cleared by a cpu read of the data in the receiver buffer register or the fifo. bit 1: lsr1 is the overrun error (oe) bit. an overrun error indicates that data in the receiver buffer register is not read by the cpu before the next character is transferred into the receiver buffer register overwriting the previous character. the oe indicator is cleared whenever the cpu reads the contents of the lsr. an overrun error occurs in the fifo mode after the fifo is full and the next character is completely received. the overrun error is detected by the cpu on the first lsr read after it happens. the character in the shift register is not transferred to the fifo, but it is overwritten. bit 2: lsr2 is the parity error (pe) bit. a parity error indicates that the received data character does not have the correct parity as selected by lcr3 and lcr4. the pe bit is set upon detection of a parity error and is cleared when the cpu reads the contents of the lsr. in the fifo mode, the parity error is associated with a particular character in the fifo. lsr2 reflects the error when the character is at the top of the fifo. bit 3: lsr3 is the framing error (fe) bit. a framing error indicates that the received character does not have a valid stop bit. lsr3 is set when the stop bit following the last data bit or parity bit is detected as a zero bit (spacing level). the fe indicator is cleared when the cpu reads the contents of the lsr. in the fifo mode, the framing error is associated with a particular character in the fifo. lsr3 reflects the error when the character is at the top of the fifo.
tl16c554, tl16c554i asynchronous communications element slls165d january 1994 revised july 1998 22 post office box 655303 ? dallas, texas 75265 principles of operation line status register (lsr) (continued) bit 4: lsr4 is the break interrupt (bi) bit. break interrupt is set when the received data input is held in the spacing (low) state for longer than a full word transmission time (start bit + data bits + parity + stop bits). the bi indicator is cleared when the cpu reads the contents of the lsr. in the fifo mode, this is associated with a particular character in the fifo. lsr2 reflects the bi when the break character is at the top of the fifo. the error is detected by the cpu when its associated character is at the top of the fifo during the first lsr read. only one zero character is loaded into the fifo when bi occurs. lsr1 lsr4 are the error conditions that produce a receiver line status interrupt (priority 1 interrupt in the interrupt identification register) when any of the conditions are detected. this interrupt is enabled by setting ier2 in the interrupt enable register. bit 5: lsr5 is the transmitter holding register empty (thre) bit. thre indicates that the ace is ready to accept a new character for transmission. the thre bit is set when a character is transferred from the transmitter holding register (thr) into the transmitter shift register (tsr). lsr5 is cleared by the loading of the thr by the cpu. lsr5 is not cleared by a cpu read of the lsr. in the fifo mode, when the transmit fifo is empty, this bit is set. it is cleared when one byte is written to the transmit fifo. when the thre interrupt is enabled by ier1, thre causes a priority 3 interrupt in the iir. if thre is the interrupt source indicated in iir, intrpt is cleared by a read of the iir. bit 6: lsr6 is the transmitter register empty (temt) bit. temt is set when the thr and the tsr are both empty. lsr6 is cleared when a character is loaded into thr and remains low until the character is transferred out of txx. temt is not cleared by a cpu read of the lsr. in the fifo mode, when both the transmitter fifo and shift register are empty, this bit is set. bit 7: lsr7 is the receiver fifo error bit. the lsr7 bit is cleared in the tl16c450 mode (see fcr bit 0). in the fifo mode, it is set when at least one of the following data errors is in the fifo: parity error, framing error, or break interrupt indicator. it is cleared when the cpu reads the lsr if there are no subsequent errors in the fifo. note the lsr may be written. however, this function is intended only for factory test. it should be considered as read only by applications software. table 6. line status register bits lsr bits 1 0 lsr0 data ready (dr) ready not ready lsr1 overrun error (oe) error no error lsr2 parity error (pe) error no error lsr3 framing error (fe) error no error lsr4 break interrupt (bi) break no break lsr5 transmitter holding register empty (thre) empty not empty lsr6 transmitter register empty (temt) empty not empty lsr7 receiver fifo error error in fifo no error in fifo
tl16c554, tl16c554i asynchronous communications element slls165d january 1994 revised july 1998 23 post office box 655303 ? dallas, texas 75265 principles of operation modem control register (mcr) the mcr controls the interface with the modem or data set as described in figure 16. mcr can be written and read. the rts and dtr outputs are directly controlled by their control bits in this register. a high input asserts a low signal (active) at the output terminals. mcr bits 0, 1, 2, 3, and 4 are shown as follows: bit 0: when mcr0 is set, the dtr output is forced low. when mcr0 is cleared, the dtr output is forced high. the dtr output of the serial channel may be input into an inverting line driver in order to obtain the proper polarity input at the modem or data set. bit1: when mcr1 is set, the rts output is forced low. when mcr1 is cleared, the rts output is forced high. the rts output of the serial channel may be input into an inverting line driver to obtain the proper polarity input at the modem or data set. bit 2: mcr2 has no affect on operation. bit 3: when mcr3 is set, the external serial channel interrupt is enabled. bit 4: mcr4 provides a local loopback feature for diagnostic testing of the channel. when mcr4 is set, serial output txx is set to the marking (high) state and sin is disconnected. the output of the tsr is looped back into the rsr input. the four modem control inputs (cts , dsr , dcd , and ri ) are disconnected. the modem control outputs (dtr and rts ) are internally connected to the four modem control inputs. the modem control output terminals are forced to their inactive (high) state on the tl16c554. in the diagnostic mode, data transmitted is immediately received. this allows the processor to verify the transmit and receive data paths of the selected serial channel. interrupt control is fully operational; however, interrupts are generated by controlling the lower four mcr bits internally. interrupts are not generated by activity on the external terminals represented by those four bits. bit 5 bit 7: mcr5, mcr6, and mcr7 are permanently cleared. data terminal ready 0 = dtr output inactive (high) 1 = dtr output active (low) modem control register mcr 7 mcr 6 mcr 5 mcr 4 mcr 3 mcr 2 loop 0 = loop disabled 1 = loop enabled bits are set to logic 0 request to send 0 = rts output inactive (high) 1 = rts output active (low) mcr 1 mcr 0 out1 (internal) out2 (internal) no affect on external operation 0 = external interrupt disabled 1 = external interrupt enabled figure 16. modem control register contents
tl16c554, tl16c554i asynchronous communications element slls165d january 1994 revised july 1998 24 post office box 655303 ? dallas, texas 75265 principles of operation modem status register (msr) the msr provides the cpu with status of the modem input lines for the modem or peripheral devices. the msr allows the cpu to read the serial channel modem signal inputs by accessing the data bus interface of the ace. it also reads the current status of four bits of the msr that indicate whether the modem inputs have changed since the last reading of the msr. the delta status bits are set when a control input from the modem changes states and are cleared when the cpu reads the msr. the modem input lines are cts , dsr, and dcd . msr4 msr7 are status indicators of these lines. a status bit = 1 indicates the input is low. when the status bit is cleared, the input is high. when the modem status interrupt in the ier is enabled (iir3 is set), an interrupt is generated whenever msr0 msr3 is set. the msr is a priority 4 interrupt. the contents of the msr are described in table 7. bit 0: msr0 is the delta clear-to-send ( d cts) bit. dcts indicates that the cts input to the serial channel has changed state since it was last read by the cpu. bit 1: msr1 is the delta data set ready ( d dsr) bit. d dsr indicates that the dsr input to the serial channel has changed states since the last time it was read by the cpu. bit 2: msr2 is the trailing edge of ring indicator (teri) bit. teri indicates that the rix input to the serial channel has changed states from low to high since the last time it was read by the cpu. high-to-low transitions on ri do not activate teri. bit 3: msr3 is the delta data carrier detect ( d dcd) bit. d dcd indicates that the dcd input to the serial channel has changed states since the last time it was read by the cpu. bit 4: msr4 is the clear-to-send (cts) bit. cts is the complement of the cts input from the modem indicating to the serial channel that the modem is ready to receive data from sout. when the serial channel is in the loop mode (mcr4 = 1), msr4 reflects the value of rts in the mcr. bit 5: msr5 is the data set ready dsr bit. dsr is the complement of the dsr input from the modem to the serial channel that indicates that the modem is ready to provide received data from the serial channel receiver circuitry. when the channel is in the loop mode (mcr4 is set), msr5 reflects the value of dtr in the mcr. bit 6: msr6 is the ring indicator (ri) bit. ri is the complement of the rix inputs. when the channel is in the loop mode (mcr4 is set), msr6 reflects the value of out1 in the mcr. bit 7: msr7 is the data carrier detect (dcd) bit. data carrier detect indicates the status of the data carrier detect (dcd ) input. when the channel is in the loop mode (mcr4 is set), msr7 reflects the value of out2 in the mcr. reading the msr clears the delta modem status indicators but has no affect on the other status bits. for lsr and msr, the setting of status bits is inhibited during status register read operations. if a status condition is generated during a read ior operation, the status bit is not set until the trailing edge of the read. when a status bit is set during a read operation and the same status condition occurs, that status bit is cleared at the trailing edge of the read instead of being set again. in the loopback mode when modem status interrupts are enabled, cts , dsr , ri, and dcd inputs are ignored; however, a modem status interrupt can still be generated by writing to mcr3 mcr0. applications software should not write to the msr.
tl16c554, tl16c554i asynchronous communications element slls165d january 1994 revised july 1998 25 post office box 655303 ? dallas, texas 75265 principles of operation modem status register (msr) (continued) table 7. modem status register bits msr bit mnemonic description msr0 d cts delta clear to send msr1 d dsr delta data set ready msr2 teri trailing edge of ring indicator msr3 d dcd delta data carrier detect msr4 cts clear to send msr5 dsr data set ready msr6 ri ring indicator msr7 dcd data carrier detect programming the serial channel of the ace is programmed by the control registers lcr, ier, dll, dlm, mcr, and fcr. these control words define the character length, number of stop bits, parity, baud rate, and modem interface. while the control registers can be written in any order, the ier should be written last because it controls the interrupt enables. once the serial channel is programmed and operational, these registers can be updated any time the ace serial channel is not transmitting or receiving data. programmable baud rate generator the ace serial channel contains a programmable baud rate generator (brg) that divides the clock (dc to 8 mhz) by any divisor from 1 to (2 16 1). two 8-bit divisor latch registers store the divisor in a 16-bit binary format. these divisor latch registers must be loaded during initialization. upon loading either of the divisor latches, a 16-bit baud counter is immediately loaded. this prevents long counts on initial load. the brg can use any of three different popular frequencies to provide standard baud rates. these frequencies are 1.8432 mhz, 3.072 mhz, and 8 mhz. with these frequencies, standard bit rates from 50 kbps to 512 kbps are available. tables 8, 9, 10, and 11 illustrate the divisors needed to obtain standard rates using these three frequencies. the output frequency of the baud rate generator is 16 the data rate [divisor # = clock + (baud rate 16)] referred to in this document as rclk.
tl16c554, tl16c554i asynchronous communications element slls165d january 1994 revised july 1998 26 post office box 655303 ? dallas, texas 75265 principles of operation programmable baud rate generator (continued) table 8. baud rates using an 1.8432-mhz crystal baud rate desired divisor (n) used to generate 16 clock percent error difference between desired and actual 50 2304 e 75 1536 e 110 1047 0.026 134.5 857 0.058 150 768 e 300 384 e 600 192 e 1200 96 e 1800 64 e 2000 58 0.690 2400 48 e 3600 32 e 4800 24 e 7200 16 e 9600 12 e 19200 6 e 38400 3 e 56000 2 2.860 table 9. baud rates using an 3.072-mhz crystal baud rate desired divisor (n) used to generate 16 clock percent error difference between desired and actual 50 3840 e 75 2560 e 110 1745 0.026 134.5 1428 0.034 150 1280 e 300 640 e 600 320 e 1200 160 e 1800 107 0.312 2000 96 e 2400 80 e 3600 53 0.628 4800 40 e 7200 27 1.230 9600 20 e 19200 10 e 38400 5 e
tl16c554, tl16c554i asynchronous communications element slls165d january 1994 revised july 1998 27 post office box 655303 ? dallas, texas 75265 principles of operation programmable baud rate generator (continued) table 10. baud rates using an 8-mhz clock baud rate desired divisor (n) used to generate 16 clock percent error difference between desired and actual 50 10000 e 75 6667 0.005 110 4545 0.010 134.5 3717 0.013 150 333 0.010 300 1667 0.020 600 883 0.040 1200 417 0.080 1800 277 0.080 2000 250 e 2400 208 0.160 3600 139 0.080 4800 104 0.160 7200 69 0.644 9600 52 0.160 19200 26 0.160 38400 13 0.160 56000 9 0.790 128000 4 2.344 256000 2 2.344 512000 1 2.400
tl16c554, tl16c554i asynchronous communications element slls165d january 1994 revised july 1998 28 post office box 655303 ? dallas, texas 75265 principles of operation programmable baud rate generator (continued) table 11. baud rates using an 16-mhz clock baud rate desired divisor (n) used to generate 16 clock percent error difference between desired and actual 50 20000 0 75 13334 0.00 110 9090 0.01 134.5 7434 0.01 150 6666 0.01 300 3334 0.02 600 1666 0.04 1200 834 0.08 1800 554 0.28 2000 500 0.00 2400 416 0.16 3600 278 0.08 4800 208 0.16 7200 138 0.64 9600 104 0.16 19200 52 0.16 38400 26 0.16 56000 18 0.79 128000 8 2.34 256000 4 2.34 512000 2 2.34 1000000 1 0.00 receiver serial asynchronous data is input into the rxx terminal. the ace continually searches for a high-to-low transition from the idle state. when the transition is detected, a counter is reset and counts the 16 clock to 7 1/2, which is the center of the start bit. the start bit is valid when the rxx is still low. verifying the start bits prevents the receiver from assembling a false data character due to a low going noise spike on the rxx input. the lcr determines the number of data bits in a character (lcr0, lcr1). when parity is enabled, lcr3 and the polarity of parity lcr4 are needed. status for the receiver is provided in the lsr. when a full character is received including parity and stop bits, the data received indicator in lsr0 is set. the cpu reads the rbr, which clears lsr0. if the character is not read prior to a new character transfer from the rsr to the rbr, the overrun error status indicator is set in lsr1. if there is a parity error, the parity error is set in lsr2. if a stop bit is not detected, a framing error indicator is set in lsr3. in the fifo mode operation, the data character and the associated error bits are stored in the receiver fifo. if the data into rxx is a symmetrical square wave, the center of the data cells occurs within 3.125% of the actual center, providing an error margin of 46.875%. the start bit can begin as much as one 16 clock cycle prior to being detected.
tl16c554, tl16c554i asynchronous communications element slls165d january 1994 revised july 1998 29 post office box 655303 ? dallas, texas 75265 principles of operation reset after power up, the ace reset input should be held high for one microsecond to reset the ace circuits to an idle mode until initialization. a high on reset causes the following: 1. it initializes the transmitter and receiver internal clock counters. 2. it clears the lsr, except for transmitter register empty (temt) and transmit holding register empty (thre), which are set. the mcr is also cleared. all of the discrete lines, memory elements, and miscellaneous logic associated with these register bits are also cleared or turned off. the lcr, divisor latches, rbr, and transmitter buffer register are not affected. rxrdy operation in mode 0, rxrdy is asserted (low) when the receive fifo is not empty; it is released (high) when the fifo is empty. in this way, the receiver fifo is read when rxrdy is asserted (low). in mode 1, rxrdy is asserted (low) when the receive fifo has filled to the trigger level or a character time-out has occurred (four character times with no transmission of characters); it is released (high) when the fifo is empty. in this mode, multiple received characters are read by the dma device, reducing the number of times it is interrupted. rxrdy and txrdy outputs from each of the four internal aces of the tl16c554 are anded together internally. this combined signal is brought out externally to rxrdy and txrdy . following the removal of the reset condition (reset low), the ace remains in the idle mode until programmed. a hardware reset of the ace sets the thre and temt status bits in the lsr. when interrupts are subsequently enabled, an interrupt occurs due to thre. a summary of the effect of a reset on the ace is given in table 12. table 12. reset affects on registers and signals register/signal reset control reset state interrupt enable register reset all bits cleared (0 3 forced and 4 7 permanent) interrupt identification register reset bit 0 is set, bits 1, 2, 3, 6, and 7 are cleared, bits 4 5 are permanently cleared line control register reset all bits cleared modem control register reset all bits cleared (5 7 permanent) fifo control register reset all bits cleared line status register reset all bits cleared, except bits 5 and 6 are set modem status register reset bits 0 3 cleared, bits 4 7 input signals txx reset high interrupt (rcvr errs) read lsr/reset low interrupt (receiver data ready) read rbr/reset low interrupt (thre) read iir/write thr/reset low interrupt (modem status changes) read msr/reset low rts reset high dtr reset high
tl16c554, tl16c554i asynchronous communications element slls165d january 1994 revised july 1998 30 post office box 655303 ? dallas, texas 75265 principles of operation scratchpad register the scratch register is an 8-bit read/write register that has no affect on either channel in the ace. it is intended to be used by the programmer to hold data temporarily. txrdy operation in mode 0, txrdy is asserted (low) when the transmit fifo is empty; it is released (high) when the fifo contains at least one byte. in this way, the fifo is written with 16 bytes when txrdy is asserted (low). in mode 1, txrdy is asserted (low) when the transmit fifo is not full; in this mode, the transmit fifo is written with another byte when txrdy is asserted (low). driver optional driver external clock optional clock output oscillator clock to baud generator logic v cc crystal oscillator clock to baud generator logic rx2 v cc c1 r p c2 xtal1 xtal1 xtal2 xtal2 typical crystal oscillator network crystal r p rx2 c1 c2 3.1 mhz 1 m w 1.5 k w 10 30 pf 40 60 pf 1.8 mhz 1 m w 1.5 k w 10 30 pf 40 60 pf figure 17. typical clock circuits
tl16c554, tl16c554i asynchronous communications element slls165d january 1994 revised july 1998 31 post office box 655303 ? dallas, texas 75265 mechanical data fn (s-pqcc-j**) plastic j-leaded chip carrier 4040005 / b 03/95 20 pin shown 0.026 (0,66) 0.032 (0,81) d2 / e2 0.020 (0,51) min 0.180 (4,57) max 0.120 (3,05) 0.090 (2,29) d2 / e2 0.013 (0,33) 0.021 (0,53) seating plane max d2 / e2 0.219 (5,56) 0.169 (4,29) 0.319 (8,10) 0.469 (11,91) 0.569 (14,45) 0.369 (9,37) max 0.356 (9,04) 0.456 (11,58) 0.656 (16,66) 0.008 (0,20) nom 1.158 (29,41) 0.958 (24,33) 0.756 (19,20) 0.191 (4,85) 0.141 (3,58) min 0.441 (11,20) 0.541 (13,74) 0.291 (7,39) 0.341 (8,66) 18 19 14 13 d d1 1 3 9 e1 e 4 8 min max min pins ** 20 28 44 0.385 (9,78) 0.485 (12,32) 0.685 (17,40) 52 68 84 1.185 (30,10) 0.985 (25,02) 0.785 (19,94) d/e 0.395 (10,03) 0.495 (12,57) 1.195 (30,35) 0.995 (25,27) 0.695 (17,65) 0.795 (20,19) no. of d1 / e1 0.350 (8,89) 0.450 (11,43) 1.150 (29,21) 0.950 (24,13) 0.650 (16,51) 0.750 (19,05) 0.004 (0,10) m 0.007 (0,18) 0.050 (1,27) notes: a. all linear dimensions are in inches (millimeters). b. this drawing is subject to change without notice. c. falls within jedec ms-018
tl16c554, tl16c554i asynchronous communications element slls165d january 1994 revised july 1998 32 post office box 655303 ? dallas, texas 75265 mechanical data pn (s-pqfp-g80) plastic quad flatpack 4040135 / b 11/96 0,17 0,27 0,13 nom 40 21 0,25 0,45 0,75 0,05 min seating plane gage plane 41 60 61 80 20 sq sq 1 13,80 14,20 12,20 9,50 typ 11,80 1,45 1,35 1,60 max 0,08 0,50 m 0,08 0 7 notes: a. all linear dimensions are in millimeters. b. this drawing is subject to change without notice. c. falls within jedec ms-026
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