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TL16C554, TL16C554I ASYNCHRONOUS COMMUNICATIONS ELEMENT
SLLS165F - JANUARY 1994 - REVISED AUGUST 2001
D D D D D D D D
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 (216 - 1) and Generate an Internal 16 x 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
D
D D D D
D D D
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 (216 - 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.
Copyright 2001, Texas Instruments Incorporated
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.
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FN PACKAGE (TOP VIEW)
DSRA CTSA DTRA VCC RTSA INTA CSA TXA IOW TXB CSB INTB RTSB GND DTRB CTSB DSRB
9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25
DCDA RIA RXA GND D7 D6 D5 D4 D3 D2 D1 D0 INTN VCC RXD RID DCDD
87 6 5432 1 68 67 66 65 64 63 62 61 60 59 58 57 56 55 54 53 52 51 50 49 48 47 46 45 44 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43
DSRD CTSD DTRD GND RTSD INTD CSD TXD IOR TXC CSC INTC RTSC VCC DTRC CTSC DSRC
NC - No internal connection
2
DCDB RIB RXB VCC NC A2 A1 A0 XTAL1 XTAL2 RESET RXRDY TXRDY GND RXC RIC DCDC
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PN PACKAGE (TOP VIEW)
NC DCDC RIC RXC GND TXRDY RXRDY RESET NC XTAL2 XTAL1 NC A0 A1 A2 VCC RXB NC DSRC CTSC DTRC VCC RTSC INTC CSC TXC IOR NC TXD CSD INTD RTSD GND DTRD CTSD DSRD NC
60 59 58 57 56 55 54 53 52 51 50 49 48 47 46 45 44 43 42 41 61 62 63 64 65 66 67 68 69 70 71 72 73 74 75 76 77 78 79 80 123 45 6 40 39 38 37 36 35 34 33 32 31 30 29 28 27 26 25 24 23 22 21 7 8 9 10 11 12 13 14 15 16 17 18 19 20
RIB DCDB NC NC DSRB CTSB DTRB GND RTSB INTB CSB TXB IOW NC TXA CSA INTA RTSA VCC DTRA CTSA DSRA NC
NC - No internal connection
NC DCDD RID RXD VCC INTN D0 D1 D2 NC D3 D4 D5 D6 D7 GND RXA RIA DCDA NC
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TL16C554, TL16C554I ASYNCHRONOUS COMMUNICATIONS ELEMENT
SLLS165F - JANUARY 1994 - REVISED AUGUST 2001
functional block diagram
D7 - D0 Data Bus 8 TL16C550B Circuitry Receive Control Logic RXx
A2 - A0 CSx IOR, IOW RESET INTx TXRDY, RXRDY
Control Logic
TL16C550B Circuitry
Transmit Control Logic
TXx
Interrupt Logic
TL16C550B Circuitry CTSx RTSx DSRx DTRx RIx DCDx
XTAL1 XTAL2
Clock Circuit
TL16C550B Circuitry
Modem Control Logic
For TL16C550 circuitry, refer to the TL16C550B data sheet.
Terminal Functions
TERMINAL NAME A0 A1 A2 CSA, CSB, CSC, CSD CTSA, CTSB, CTSC, CTSD D7 - D0 DCDA, DCDB, DCDC, DCDD DSRA, DSRB, DSRC, DSRD DTRA, DTRB, DTRC, DTRD FN NO. 34 33 32 16, 20, 50, 54 11, 25, 45, 59 66 - 68 1-5 9, 27, 43, 61 10, 26, 44, 60 12, 24, 46, 58 PN NO. 48 47 46 28, 33, 68, 73 23, 38, 63, 78 15-11, 9-7 19,42, 59, 2 22, 39, 62, 79 24, 37, 64, 77 I/O I DESCRIPTION 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. Chip select. Each chip select (CSx) enables read and write operations to its respective channel. 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. 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). 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. 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. 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. Signal and power ground 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 Brought low or allowed to float Brought high OPERATION OF INTERRUPTS 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. Interrupts are always enabled, overriding the OUT2 enables.
I I I/O I
I O
GND INTN
6, 23, 40, 57 65
16, 36, 56, 76 6
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Terminal Functions (Continued)
TERMINAL NAME INTA, INTB, INTC, INTD FN NO. 15, 21, 49, 55 PN NO. 27, 34, 67, 74 I/O O DESCRIPTION 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. Read strobe. A low level on IOR transfers the contents of the TL16C554 data bus to the external CPU bus. Write strobe. IOW allows the CPU to write into the selected address by the address register. 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. 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. 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. 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. Receive ready. RXRDY goes low when the receive FIFO is full. It can be used as a single transfer or multitransfer. 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. Transmit ready. TXRDY goes low when the transmit FIFO is full. It can be used as a single transfer or multitransfer function. Power supply I O 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. Crystal output 2 or buffered clock output (see XTAL1).
IOR IOW RESET RIA, RIB, RIC, RID RTSA, RTSB, RTSC, RTSD RXA, RXB RXC, RXD RXRDY TXA, TXB TXC, TXD TXRDY VCC XTAL1 XTAL2
52 18 37 8, 28, 42, 62 14, 22, 48, 56 7, 29, 41, 63 38 17, 19, 51, 53 39 13, 30, 47, 64 35 36
70 31 53 18, 43, 58, 3 26, 35, 66, 75 17, 44, 57, 4 54 29, 32, 69, 72 55 5, 25, 45, 65 50 51
I I I I O
I O O O
absolute maximum ratings over free-air temperature range (unless otherwise noted)
Supply voltage range, VCC (see Note 1) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . - 0.5 V to 7 V Input voltage range at any input, VI . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . - 0.5 V to 7 V Output voltage range, VO . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . - 0.5 V to VCC + 3 V Continuous total power dissipation at (or below) 70C . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 500 mW Operating free-air temperature range, TA: TL16C554 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . - 0C to 70C TL16C554I . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . -40C to 85C Storage temperature range, Tstg . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . - 65C to 150C
Stresses beyond those listed under "absolute maximum ratings" may cause permanent damage to the device. These are stress ratings only, and functional operation of the device at these or any other conditions beyond those indicated under "recommended operating conditions" 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.
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recommended operating conditions
MIN Supply voltage, VCC Clock high-level input voltage at XTAL1, VIH(CLK) Clock low-level input voltage at XTAL1, VIL(CLK) High-level input voltage, VIH Low-level input voltage, VIL Clock frequency, fclock O erating Operating free-air tem erature, TA temperature TL16C554 TL16C554I 0 -40 4.75 2 - 0.5 2 - 0.5 NOM 5 MAX 5.25 VCC 0.8 VCC 0.8 16 70 85 UNIT V V V V V MHz C C
electrical characteristics over recommended ranges of operating free-air temperature and supply voltage (unless otherwise noted)
PARAMETER VOH VOL IIkg IOZ High-level output voltage Low-level output voltage Input leakage current High-impedance output current IOH = - 1 mA IOL = 1.6 mA VCC = 5.25 V, VI = 0 to 5.25 V, GND = 0, All other terminals floating TEST CONDITIONS MIN 2.4 0.4 10 20 TYP MAX UNIT V V A A
VCC = 5.25 V, GND = 0, VO = 0 to 5.25 V, Chip selected in write mode or chip deselected VCC = 5.25 V, TA = 25C, 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 15 VCC = 0, VSS = 0, All other terminals grounded, grounded 25C TA = 25 C MHz, f = 1 MHz 20 6 10
ICC Ci(XTAL1) Co(XTAL2) Ci
Supply current
50
mA
Clock input capacitance Clock output capacitance Input capacitance
20 30 10 20
pF pF pF pF
Co Output capacitance All typical values are at VCC = 5 V, TA = 25C. 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 tw1 tw2 tw3 Pulse duration, clock high (external clock) Pulse duration, clock low (external clock) Pulse duration, RESET 31 31 1000 MAX UNIT ns ns ns
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read cycle timing requirements over recommended ranges of operating free-air temperature and supply voltage (see Figure 4)
MIN tw4 tsu1 tsu2 th1 th2 td1 Pulse duration, IOR low Setup time, CSx valid before IOR low (see Note 2) Setup time, A2 - A0 valid before IOR low (see Note 2) Hold time, A2 - A0 valid after IOR high (see Note 2) Hold time, CSx valid after IOR high (see Note 2) Delay time, tsu2 + tw4 + td2 (see Note 3) 75 10 15 0 0 140 MAX UNIT ns ns ns ns ns ns
td2 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, td1 = 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 tw5 tsu3 tsu4 tsu5 th3 th4 th5 td3 Pulse duration, IOW Setup time, CSx valid before IOW (see Note 2) Setup time, A2 - A0 valid before IOW (see Note 2) Setup time, D7 - D0 valid before IOW Hold time, A2 - A0 valid after IOW (see Note 2) Hold time, CSx valid after IOW (see Note 2) Hold time, D7 - D0 valid after IOW Delay time, tsu4 + tw5 + td4 50 10 15 10 5 5 25 120 55 MAX UNIT ns ns ns ns ns ns ns ns ns
td4 Delay time, IOW to IOW or IOR NOTE 2: The internal address strobe is always active.
read cycle switching characteristics over recommended ranges of operating free-air temperature and supply voltage, CL = 100 pF (see Note 4 and Figure 4)
PARAMETER ten tdis Enable time, IOR to D7 - D0 valid Disable time, IOR to D7 - D0 released 0 MIN MAX 30 20 UNIT ns ns
NOTE 4: VOL and VOH (and the external loading) determine the charge and discharge time.
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transmitter switching characteristics over recommended ranges of operating free-air temperature and supply voltage (see Figures 6, 7, and 8)
PARAMETER td5 td6 td7 td8 tpd1 tpd2 tpd3 Delay time, INTx to TXx at start Delay time, TXx at start to INTx Delay time, IOW high or low (WR THR) to INTx Delay time, TXx at start to TXRDY Propagation delay time, IOW (WR THR) to INTx Propagation delay time, IOR (RD IIR) to INTx Propagation delay time, IOW (WR THR) to TXRDY See Note 5 See Note 5 CL = 100 pF CL = 100 pF CL = 100 pF CL = 100 pF TEST CONDITIONS MIN 8 8 16 MAX 24 8 32 8 35 30 50 UNIT RCLK cycles RCLK cycles RCLK cycles RCLK cycles ns ns ns
NOTE 5: If the transmitter interrupt delay is active, this delay is lengthened by one character time minus the last stop bit time.
receiver switching characteristics over recommended ranges of operating free-air temperature and supply voltage (see Figures 9 through 13)
PARAMETER td9 tpd4 tpd5 Delay time, stop bit to INTx or stop bit to RXRDY or read RBR to set interrupt Propagation delay time, Read RBR/LSR to INTx/LSR interrupt Propagation delay time, IOR RCLK to RXRDY TEST CONDITIONS See Note 6 CL = 100 pF, See Note 7 See Note 7 MIN MAX 1 40 30 UNIT RCLK cycle ns 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, CL = 100 pF (see Figure 14)
PARAMETER tpd6 tpd7 tpd8 tpd9 Propagation delay time, IOW (WR MCR) to RTSx, DTRx Propagation delay time, modem input CTSx, DSRx, and DCDx to INTx Propagation delay time, IOR (RD MSR) to interrupt Propagation delay time, RIx to INTx MIN MAX 50 30 35 30 UNIT ns ns ns ns
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PARAMETER MEASUREMENT INFORMATION
tw1 Clock (XTAL1) 2V 0.8 V 2V 0.8 V tw2 fclock = 16 MHz MAX (a) CLOCK INPUT VOLTAGE WAVEFORM 2V 0.8 V
RESET
tw3 (b) RESET VOLTAGE WAVEFORM
Figure 1. Clock Input and RESET Voltage Waveforms
2.54 V
Device Under Test TL16C554
680
82 pF (see Note A)
NOTE A: This includes scope and jig capacitance.
Figure 2. Output Load Circuit
Serial Channel 1 Buffers Serial Channel 2 Buffers Serial Channel 3 Buffers Serial Channel 4 Buffers
Data Bus
9-Pin D Connector
Address Bus TL16C554 Quadruple ACE 9-Pin D Connector
Control Bus
9-Pin D Connector
9-Pin D Connector
Figure 3. Basic Test Configuration
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PARAMETER MEASUREMENT INFORMATION
A2, A1, A0 50% Valid th1 Valid CSx 50% tsu1 td1 tsu2 IOR 50% Active 50% td2 50% Active th2 50% 50%
tw4 IOW ten D7 - D0 Valid Data
or 50% Active
tdis
Figure 4. Read Cycle Timing Waveforms
A2, A1, A0
50%
Valid th3 Valid
50%
CSx
50% tsu3 td3 tsu4 th4
50%
IOW
50% Active tw5
50% td4
50%
Active or
50% IOR tsu5 D7 - D0 Valid Data th5
Active
Figure 5. Write Cycle Timing Waveforms
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PARAMETER MEASUREMENT INFORMATION
Start TXx 50% td5 INTx tpd1 td7 IOW 50% (WR THR) IOR (RD IIR) 50% tpd1 50% tpd2 50% 50% 50% Data (5 - 8) Parity 50% Stop (1 - 2) Start
td6 50% 50%
50%
Figure 6. Transmitter Timing Waveforms
IOW (WR THR)
Byte #1 50%
TXx
Data tpd3
Parity
Stop td8
50%
Start
TXRDY FIFO Empty
50%
50%
Figure 7. Transmitter Ready Mode 0 Timing Waveforms
IOW (WR THR)
Byte #16 50% Start
TXx
Data
Parity
Stop
Start
50%
tpd3 TXRDY 50% FIFO Full
td8 50%
Figure 8. Transmitter Ready Mode 1 Timing Waveforms
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PARAMETER MEASUREMENT INFORMATION
TL16C450 Mode: SIN (receiver input data) Sample Clock td9 INTx (data ready or RCVR ERR) 50% tpd4 50% Active 50% Start Data Bits (5 - 8) Parity Stop
IOR
Figure 9. Receiver Timing Waveforms
RXx
Start
Data Bits (5 - 8)
Parity
Stop
Sample Clock (FIFO at or above trigger level) (FIFO below trigger level)
INTx (trigger interrupt) (FCR6, 7 = 0, 0) td9 IOR (RD RBR) LSR Interrupt
50% tpd4 50%
50%
Active
50% tpd4
50%
IOR (RD LSR)
50%
Active
Figure 10. Receiver FIFO First Byte (Sets RDR) Waveforms
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PARAMETER MEASUREMENT INFORMATION
RXx
Stop
Sample Clock td9 (see Note A) INTx (time-out or trigger level) Interrupt INTx Interrupt td9 IOR (RD LSR) 50% 50% tpd4 50% Top Byte of FIFO tpd4 Active 50% 50% (FIFO at or above trigger level) (FIFO below trigger level)
IOR (RD RBR)
Active Previous BYTE Read From FIFO
50%
50%
Active
NOTE A: This is the reading of the last byte in the FIFO.
Figure 11. Receiver FIFO After First Byte (After RDR Set) Waveforms
IOR (RD RBR)
50%
Active (see Note A)
RXx
Sample Clock
Stop
td9 (see Note B)
RXRDY
50%
tpd5
50%
NOTES: A. This is the reading of the last byte in the FIFO. B. If FCR0 = 1, then td9 = 3 RCLK cycles. For a time-out interrupt, td9 = 8 RCLK cycles.
Figure 12. Receiver Ready Mode 0 Timing Waveforms
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PARAMETER MEASUREMENT INFORMATION
IOR (RD RBR) SIN (first byte that reaches the trigger level) Sample Clock
50%
Active (see Note A)
Stop
td9 (see Note B)
RXRDY
50%
tpd5
50%
NOTES: A. This is the reading of the last byte in the FIFO. B. If FCR0 = 1, td9 = 3 RCLK cycles. For a trigger change level interrupt, td9 = 8 RCLK.
Figure 13. Receiver Ready Mode 1 Timing Waveforms
IOW (WR MCR)
50% tpd6 50%
50% tpd6 50%
RTSx, DTRx CTSx, DSRx, DCDx tpd7 INTx 50%
50%
50% tpd7 50% 50% 50%
tpd8 IOR (RD MSR) 50%
tpd9
RIx
50%
Figure 14. Modem Control Timing Waveforms
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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 Line control register FIFO control register Modem control register Divisor latch LSB Divisor latch MSB Interrupt enable register MNEMONIC LCR FCR MCR DLL DLM IER STATUS Line status register Modem status register MNEMONIC LSR MSR DATA Receiver buffer register Transmitter holding register MNEMONIC RBR THR
Table 2. Register Selection
DLAB 0 0 X X X X X X 1 1 A2 0 0 0 0 1 1 1 1 0 0 A1 0 0 1 1 0 0 1 1 0 0 A0 0 1 0 1 0 1 0 1 0 1 Line status register Modem status register Scratchpad register Scratchpad register LSB divisor latch MSB divisor latch Interrupt identification register READ MODE Receiver buffer register WRITE MODE Transmitter holding register Interrupt enable register FIFO control register Line control register Modem control register
X = irrelevant, 0 = low level, 1 = high level The serial channel is accessed when either CSA or CSD is low. 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.
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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 0 0 0 1 1 REGISTER MNEMONIC RBR (read only) THR (write only) DLL DLM IER REGISTER ADDRESS BIT 7 Data Bit 7 (MSB) Data BIt 7 Bit 7 Bit 15 0 BIT 6 Data Bit 6 Data BIt 6 Bit 6 Bit 14 0 BIT 5 Data Bit 5 Data BIt 5 Bit 5 Bit 13 0 BIT 4 Data Bit 4 Data BIt 4 Bit 4 Bit 12 0 BIT 3 Data Bit 3 Data BIt 3 Bit 3 Bit 11 (EDSSI) Enable modem status interrupt BIT 2 Data Bit 2 Data BIt 2 Bit 2 Bit 10 (ERLSI) Enable receiver line status interrupt BIT 1 Data Bit 1 Data BIt 1 Bit 1 Bit 9 (ETBEI) Enable transmitter holding register empty interrupt Receiver FIFO reset Interrupt ID Bit (1) (WLSB1) Word length select bit 1 (RTS) Request to send BIT 0 Data Bit 0 (LSB) Data BIt 0 Bit 0 Bit 8 (ERBI) Enable received data available interrupt FIFO Enable
2
FCR (write only) IIR (read only) LCR
Receiver Trigger (MSB) FIFOs Enabled (DLAB) Divisor latch access bit 0
Receiver Trigger (LSB) FIFOs Enabled Set break
Reserved
Reserved
DMA mode select Interrupt ID Bit (3) (PEN) Parity enable OUT2 Enable external interrupt (INT) (FE) Framing error
Transmit FIFO reset Interrupt ID Bit (2) (STB) Number of stop bits Reserved
2 3
0 Stick parity
0 (EPS) Even parity select Loop
0 If interrupt pending (WLSB0) Word length select bit 0 (DTR) Data terminal ready
4
MCR
0
0
5
LSR
Error in receiver FIFO
(TEMT) Transmitter registers empty (RI) Ring indicator
(THRE) Transmitter holding register empty (DSR) Data set ready Bit 5
(BI) Break interrupt
(PE) Parity error
(OE) Overrun error
(DR) Data ready
6
MSR
(DCD) Data carrier detect
(CTS) Clear to send Bit 4
( DCD) Delta data carrier detect Bit 3
(TERI) Trailing edge ring indicator Bit 2
( DSR) Delta data set ready Bit 1
( CTS) Delta clear to send Bit 0
7 SCR Bit 7 Bit 6 DLAB = 1 These bits are always 0 when FIFOs are disabled.
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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.
D D D D D D
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 7 0 0 1 1 6 0 1 0 1 RECEIVER FIFO TRIGGER LEVEL (BYTES) 01 04 08 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.
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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:
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PRINCIPLES OF OPERATION interrupt enable register (IER) (continued)
D D D D D
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:
D D D D
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 BIT 3 0 0 0 BIT 2 0 1 1 BIT 1 0 1 0 BIT 0 1 0 0 PRIORITY LEVEL -- First Second INTERRUPT SET AND RESET FUNCTIONS INTERRUPT RESET CONTROL -- LSR read RBR read until FIFO drops below the trigger level RBR read
INTERRUPT TYPE None Receiver line status Received data available
INTERRUPT SOURCE None OE, PE, FE, or BI Receiver data available or trigger level reached 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. THRE
1
1
0
0
Second
Character time-out indicator
0
0
1
0
Third
THRE
IIR read if THRE is the interrupt source or THR write
0
0
0
0
Fourth
Modem status
CTS, DSR, RI, or DCD
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PRINCIPLES OF OPERATION interrupt identification register (IIR) (continued)
D D D D D
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.
D D D D D D
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. Step 2. Step 3. Load a zero byte in response to the transmitter holding register empty (THRE) status indicator. Set the break in response to the next THRE status indicator. 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.
D
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.
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PRINCIPLES OF OPERATION line control register (LCR) (continued)
LINE CONTROL REGISTER LCR 7 LCR LCR 6 5 LCR 4 LCR 3 LCR LCR 2 1 LCR 0 0 0 1 1 0 = 5 Data Bits 1 = 6 Data Bits 0 = 7 Data Bits 1 = 8 Data bits
Word Length Select
Stop Bit Select Parity Enable Even Parity Select Stick Parity Break Control Divisor Latch Access BIt
0 = 1 Stop Bit 1 = 1.5 Stop Bits if 5 Data Bits Selected 2 Stop Bits if 6, 7, 8 Data Bits Selected 0 = Parity Disabled 1 = Parity Enabled 0 = Odd Parity 1 = Even Parity 0 = Stick Parity Disabled 1 = Stick Parity Enabled 0 = Break Disabled 1 = Break Enabled 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:
D D
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.
D D
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PRINCIPLES OF OPERATION line status register (LSR) (continued)
D
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.
D
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.
D D
Table 6. Line Status Register BIts
LSR BITS LSR0 data ready (DR) LSR1 overrun error (OE) LSR2 parity error (PE) LSR3 framing error (FE) LSR4 break interrupt (BI) LSR5 transmitter holding register empty (THRE) LSR6 transmitter register empty (TEMT) LSR7 receiver FIFO error 1 Ready Error Error Error Break Empty Empty Error in FIFO 0 Not ready No error No error No error No break Not empty Not empty No error in FIFO
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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:
D D D D D
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.
MODEM CONTROL REGISTER MCR MCR MCR MCR MCR 7 6 5 4 3 MCR MCR 2 1 MCR 0 Data Terminal Ready Request to Send Out1 (internal) Out2 (internal) 0 = DTR Output Inactive (high) 1 = DTR Output Active (low) 0 = RTS Output Inactive (high) 1 = RTS Output Active (low) No affect on external operation 0 = External Interrupt Disabled 1 = External Interrupt Enabled 0 = Loop Disabled 1 = Loop Enabled
D
Loop
Bits Are Set to Logic 0
Figure 16. Modem Control Register Contents
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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.
D D D D D D D D
Bit 0: MSR0 is the delta clear-to-send ( 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 ( DSR) bit. 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 ( DCD) bit. 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.
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PRINCIPLES OF OPERATION modem status register (MSR) (continued)
Table 7. Modem Status Register BIts
MSR BIT MSR0 MSR1 MSR2 MSR3 MSR4 MSR5 MSR6 MSR7 MNEMONIC CTS DSR TERI DCD CTS DSR RI DCD DESCRIPTION Delta clear to send Delta data set ready Trailing edge of ring indicator Delta data carrier detect Clear to send Data set ready Ring indicator 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 (216 - 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 16x the data rate [divisor # = clock + (baud rate x 16)] referred to in this document as RCLK.
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PRINCIPLES OF OPERATION programmable baud rate generator (continued)
Table 8. Baud Rates Using an 1.8432-MHz Crystal
BAUD RATE DESIRED 50 75 110 134.5 150 300 600 1200 1800 2000 2400 3600 4800 7200 9600 19200 38400 56000 DIVISOR (N) USED TO GENERATE 16 x CLOCK 2304 1536 1047 857 768 384 192 96 64 58 48 32 24 16 12 6 3 2 PERCENT ERROR DIFFERENCE BETWEEN DESIRED AND ACTUAL -- -- 0.026 0.058 -- -- -- -- -- 0.690 -- -- -- -- -- -- -- 2.860
Table 9. Baud Rates Using an 3.072-MHz Crystal
BAUD RATE DESIRED 50 75 110 134.5 150 300 600 1200 1800 2000 2400 3600 4800 7200 9600 19200 38400 DIVISOR (N) USED TO GENERATE 16 x CLOCK 3840 2560 1745 1428 1280 640 320 160 107 96 80 53 40 27 20 10 5 PERCENT ERROR DIFFERENCE BETWEEN DESIRED AND ACTUAL -- -- 0.026 0.034 -- -- -- -- 0.312 -- -- 0.628 -- 1.230 -- -- --
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PRINCIPLES OF OPERATION programmable baud rate generator (continued)
Table 10. Baud Rates Using an 8-MHz Clock
BAUD RATE DESIRED 50 75 110 134.5 150 300 600 1200 1800 2000 2400 3600 4800 7200 9600 19200 38400 56000 128000 256000 512000 DIVISOR (N) USED TO GENERATE 16 x CLOCK 10000 6667 4545 3717 333 1667 883 417 277 250 208 139 104 69 52 26 13 9 4 2 1 PERCENT ERROR DIFFERENCE BETWEEN DESIRED AND ACTUAL -- 0.005 0.010 0.013 0.010 0.020 0.040 0.080 0.080 -- 0.160 0.080 0.160 0.644 0.160 0.160 0.160 0.790 2.344 2.344 2.400
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PRINCIPLES OF OPERATION programmable baud rate generator (continued)
Table 11. Baud Rates Using an 16-MHz Clock
BAUD RATE DESIRED 50 75 110 134.5 150 300 600 1200 1800 2000 2400 3600 4800 7200 9600 19200 38400 56000 128000 256000 512000 1000000 DIVISOR (N) USED TO GENERATE 16 x CLOCK 20000 13334 9090 7434 6666 3334 1666 834 554 500 416 278 208 138 104 52 26 18 8 4 2 1 PERCENT ERROR DIFFERENCE BETWEEN DESIRED AND ACTUAL 0 0.00 0.01 0.01 0.01 - 0.02 0.04 - 0.08 0.28 0.00 0.16 - 0.08 0.16 0.64 0.16 0.16 0.16 - 0.79 - 2.34 - 2.34 - 2.34 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 16x 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 16x clock cycle prior to being detected.
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TL16C554, TL16C554I ASYNCHRONOUS COMMUNICATIONS ELEMENT
SLLS165F - JANUARY 1994 - REVISED AUGUST 2001
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 Interrupt enable register Interrupt identification register Line control register Modem control register FIFO control register Line status register Modem status register TXx Interrupt (RCVR ERRS) Interrupt (receiver data ready) Interrupt (THRE) Interrupt (modem status changes) RTS DTR RESET CONTROL Reset Reset Reset Reset Reset Reset Reset Reset Read LSR/Reset Read RBR/Reset Read IIR/Write THR/Reset Read MSR/Reset Reset Reset RESET STATE All bits cleared (0 - 3 forced and 4 - 7 permanent) Bit 0 is set, bits 1, 2, 3, 6, and 7 are cleared, Bits 4 - 5 are permanently cleared All bits cleared All bits cleared (5 - 7 permanent) All bits cleared All bits cleared, except bits 5 and 6 are set Bits 0 - 3 cleared, bits 4 - 7 input signals High Low Low Low Low High High
POST OFFICE BOX 655303
* DALLAS, TEXAS 75265
29
TL16C554, TL16C554I ASYNCHRONOUS COMMUNICATIONS ELEMENT
SLLS165F - JANUARY 1994 - REVISED AUGUST 2001
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 External Clock XTAL1
VCC XTAL1 C1 Crystal RP
VCC
Optional Driver Optional Clock Output XTAL2 Oscillator Clock to Baud Generator Logic C2
RX2 XTAL2
Oscillator Clock to Baud Generator Logic
TYPICAL CRYSTAL OSCILLATOR NETWORK CRYSTAL 3.1 MHz 1.8 MHz RP 1 M 1 M RX2 1.5 k 1.5 k C1 10 - 30 pF 10 - 30 pF C2 40 - 60 pF 40 - 60 pF
Figure 17. Typical Clock Circuits
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POST OFFICE BOX 655303
* DALLAS, TEXAS 75265
TL16C554, TL16C554I ASYNCHRONOUS COMMUNICATIONS ELEMENT
SLLS165F - JANUARY 1994 - REVISED AUGUST 2001
MECHANICAL DATA
FN (S-PQCC-J**)
20 PIN SHOWN Seating Plane 0.004 (0,10) D D1 3 1 19 0.032 (0,81) 0.026 (0,66) 4 18 D2 / E2 0.180 (4,57) MAX 0.120 (3,05) 0.090 (2,29) 0.020 (0,51) MIN
PLASTIC J-LEADED CHIP CARRIER
E
E1 D2 / E2 8 14
0.050 (1,27) 9 13 0.008 (0,20) NOM
0.021 (0,53) 0.013 (0,33) 0.007 (0,18) M
NO. OF PINS ** 20 28 44 52 68 84
D/E MIN 0.385 (9,78) 0.485 (12,32) 0.685 (17,40) 0.785 (19,94) 0.985 (25,02) 1.185 (30,10) MAX 0.395 (10,03) 0.495 (12,57) 0.695 (17,65) 0.795 (20,19) 0.995 (25,27) 1.195 (30,35) MIN
D1 / E1 MAX 0.356 (9,04) 0.456 (11,58) 0.656 (16,66) 0.756 (19,20) 0.958 (24,33) 1.158 (29,41) MIN
D2 / E2 MAX 0.169 (4,29) 0.219 (5,56) 0.319 (8,10) 0.369 (9,37) 0.469 (11,91) 0.569 (14,45) 4040005 / B 03/95
0.350 (8,89) 0.450 (11,43) 0.650 (16,51) 0.750 (19,05) 0.950 (24,13) 1.150 (29,21)
0.141 (3,58) 0.191 (4,85) 0.291 (7,39) 0.341 (8,66) 0.441 (11,20) 0.541 (13,74)
NOTES: A. All linear dimensions are in inches (millimeters). B. This drawing is subject to change without notice. C. Falls within JEDEC MS-018
POST OFFICE BOX 655303
* DALLAS, TEXAS 75265
31
TL16C554, TL16C554I ASYNCHRONOUS COMMUNICATIONS ELEMENT
SLLS165F - JANUARY 1994 - REVISED AUGUST 2001
MECHANICAL DATA
PN (S-PQFP-G80)
0,27 0,17 41
PLASTIC QUAD FLATPACK
0,50 60
0,08 M
61
40
80
0,13 NOM 21
1 9,50 TYP 12,20 SQ 11,80 14,20 SQ 13,80 1,45 1,35
20
Gage Plane
0,25 0,05 MIN 0- 7
0,75 0,45
Seating Plane 1,60 MAX 0,08 4040135 / B 11/96 NOTES: A. All linear dimensions are in millimeters. B. This drawing is subject to change without notice. C. Falls within JEDEC MS-026
32
POST OFFICE BOX 655303
* DALLAS, TEXAS 75265
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