Texas Instruments TL16C552APN, TL16C552AMHV, TL16C552AMHVB, TL16C552AIFN, TL16C552AFNR Datasheet

TL16C552A, TL16C552AM

DUAL ASYNCHRONOUS COMMUNICATIONS ELEMENT

WITH FIFO

SLLS189D – NOVEMBER 1994 – REVISED JANUARY 1999

1

POST OFFICE BOX 655303 • DALLAS, TEXAS 75265

D

IBM PC/A T Compatible

D

T wo TL16C550 ACEs

D

Enhanced Bidirectional Printer Port

D

16-Byte FIFOs Reduce CPU Interrupts

D

Up to 16-MHz Clock Rate for up to 1-Mbaud
Operation

D

Transmit, Receive, Line Status, and Data
Set Interrupts on Each Channel
Independently Controlled

D

Individual Modem Control Signals for Each
Channel

D

Programmable Serial Interface
Characteristics for Each Channel:
– 5-, 6-, 7-, or 8-Bit Characters
– Even, Odd, or No Parity Bit Generation

and Detection

– 1-, 1-1/2-, or 2-Stop Bit Generation

D

3-State Outputs Provide TTL Drive for the
Data and Control Bus on Each Channel

D

Hardware and Software Compatible With
TL16C452

28 29

INT1
INT2
SLIN
INIT
AFD
STB
GND
PD0
PD1
PD2
PD3
PD4
PD5
PD6
PD7
INT0
BDO

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

SOUT1

DTR1
RTS1
CTS1

DB0
DB1
DB2
DB3
DB4
DB5
DB6
DB7

TXRDY0

V

DD

RTS0
DTR0

SOUT0

31 32 33 34

HV or FN PACKAGE

(TOP VIEW)

ACK

PE

87 65493

GND

RI1

DSR1

CLK

CS1

TRI

PEMD

IOW

IOR

CS2

RESET

DCD0

RI0

DSR0

CS0

A2A1A0

168672

35 36 37 38 39

66 65

27

GND

CTS0

BUSY

SLCT

64 63 62 61

40 41 42 43

SIN0

TXRDY1

ENIRQ

ERR

SIN1

RXRDY1

RXRDY0

DCD1

V

DD

V

DD

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  1999, Texas Instruments Incorporated

IBM PC/AT is a trademark of International Business Machines Corporation.

TL16C552A, TL16C552AM
DUAL ASYNCHRONOUS COMMUNICATIONS ELEMENT
WITH FIFO

SLLS189D – NOVEMBER 1994 – REVISED JANUARY 1999

2

POST OFFICE BOX 655303 • DALLAS, TEXAS 75265

22 23

NC
ENIRQ
TXRDY1
SIN0
V

DD

RESET
CS2
IOR
IOW
A0
A1
A2
CS0
DSR0
RI0
DCD0
CTS0
GND
NC
NC

60
59
58
57
56
55
54
53
52
51
50
49
48
47
46
45
44
43
42
41

24

1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20

NC
NC

RXRDY1

SIN1

ERR

V

DD

SLCT

BUSY

PE

ACK

PEMD

TRI
CS1
CLK

DSR1

RI1

GND

DCD1

RXRDY0

NC

25 26 27 28

PN PACKAGE

(TOP VIEW)

PD2

79 78 77 76 7580 74

INT2

SLIN

INIT

AFD

STB

GND

PD0

DB4

DB6

SOUT1

DTR1

RTS1

CTS1

DB0

DB1

DB2

72 71 7073

29

30 31 32 33

69 68

21

NC

PD4

67 66 65 64

34 35 36 37

DB7

TXRDY0

RTS0

PD5

PD6

PD7

INT0

NC

INT1

DTR0

SOUT0

38 39 40

BDO

NC

63 62 61

PD1

PD3

NC

DB3

NC

DB5

NC

V

DD

description

The TL16C552A is an enhanced dual-channel version of the popular TL16C550B asynchronous
communications element (ACE). The device serves two serial input/output interfaces simultaneously in
microcomputer or microprocessor-based systems. 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 dual ACE can be read at any time during
functional operation by the CPU. The information obtained includes the type and condition of the transfer
operations being performed and the error conditions encountered.

In addition to its dual communications interface capabilities, the TL16C552A provides the user with a
bidirectional parallel data port that fully supports the parallel Centronics-type printer interface. The parallel port
and the two serial ports provide IBM PC/A T-compatible computers with a single device to serve the three system
ports. A programmable baud rate generator that can divide the timing reference clock input by a divisor between
1 and (2

16

– 1) is included.

The TL16C552A is available in a 68-pin plastic-leaded chip-carrier (FN) package, a 48-pin TQFP (PN) package,
and the 80-pin TQFP (PN) package. The TL16C552AM is available in a 68-pin ceramic quad flat (HV) package.

TL16C552A, TL16C552AM

DUAL ASYNCHRONOUS COMMUNICATIONS ELEMENT

WITH FIFO

SLLS189D – NOVEMBER 1994 – REVISED JANUARY 1999

3

POST OFFICE BOX 655303 • DALLAS, TEXAS 75265

functional block diagram

CTS0
DSR0
DCD0

RI0

SIN0

CS0

DB0–DB7

RTS0
DTR0
SOUT0
INT0
RXRDY0
TXRDY0

RTS1
DTR1
SOUT1
INT1
RXRDY1
TXRDY1

BDO

24
25
26
45

9

22

12
11
10
60
61
42

53–46

57
56
55
58
59

CTS1
DSR1
DCD1

RI1

SIN1

CS1

28
31
29
30
41
32
14–21

8

8

13
5
8
6
62
3

35–33
36
37
39
4

A0–A2

IOW

IOR

RESET

CLK

ERR

SLCT

BUSY

PE

ACK

PEMD

CS2

ENIRQ

63
65
66
67
68
1
38
43

8

8

PD0–PD7
INIT
AFD
STB
SLIN
INT2

44

Select

and

Control

Logic

Parallel

Port

ACE

#2

ACE

#1

3

TL16C552A, TL16C552AM
DUAL ASYNCHRONOUS COMMUNICATIONS ELEMENT
WITH FIFO

SLLS189D – NOVEMBER 1994 – REVISED JANUARY 1999

4

POST OFFICE BOX 655303 • DALLAS, TEXAS 75265

Terminal Functions

TERMINAL

NO.

I/O

DESCRIPTION

NAME

FN PN

ACK 68 10 I Line printer acknowledge. ACK goes low to indicate a successful data transfer has taken place. ACK

generates a printer port interrupt during its positive transition.

AFD 56 75 I/O

Line printer autofeed. AFD is an open-drain line that provides the printer with an active-low signal when
continuous form paper is to be autofed to the printer. AFD

has an internal pullup resistor to VDD of

approximately 10 kΩ.

A0, A1, A2 35, 34,3351, 50,49I Address. The address lines A0–A2 select the internal registers during CPU bus operations. See T able

2 for the decode of the serial channels and Table 13 for the decode of the parallel printer port.

BDO 44 63 O Bus buffer. BDO is the active-high output and is asserted when either the serial channel or the parallel

port is read. BDO controls the system bus driver (74LS245 or 54LS245).

BUSY 66 8 I Line printer busy. BUSY is an input line from the printer that goes high when the printer is not ready

to accept data.
CLK 4 14 I Clock. CLK is the external clock input to the baud rate divisor of each ACE.
CS0, CS1,

CS2

32, 3,3848, 13,54I

Chip select. Each CSx input acts as an enable for the write and read signals for serial channels 1 (CS0)

and 2 (CS1

). CS2 enables the signals to the printer port.

CTS0,
CTS1

28, 13 44, 26 I Clear to send. The logical state of each CTSx terminal is reflected in the CTS bit of the modem status

register (CTS is bit 4 of the modem status register, written as MSR4) of each ACE. A change of state

in either CTS

terminal since the previous reading of the associated MSR causes the setting of ∆CTS

(MSR0) of each modem status register.
DB0 –

DB7

14 – 21 27 – 34 I/O Data bits DB0–DB7. The data bus provides eight I/O lines with 3-state outputs for the transfer of data,

control, and status information between the TL16C552A and the CPU. These lines are normally in the

high-impedance state except during read operations. DB0 is the least significant bit (LSB) and is the

first serial data bit to be received or transmitted.
DCD0,

DCD1

29, 8 45, 18 I Data carrier detect. DCD is a modem input. Its condition can be tested by the CPU by reading MSR7

(DCD) of the modem status registers. MSR3 (∆DCD) of the modem status register indicates whether

DCD

has changed states since the previous reading of the MSR. DCD has no effect on the receiver.

DSR0,
DSR1

31, 5 47, 15 I

Data set ready. The logical state of the DSRx terminals is reflected in MSR5 of its associated modem

status register. ∆DSR (MSR1) indicates whether the associated DSRx

terminal has changed states

since the previous reading of the MSR.
DTR0,

DTR1

25, 11 38, 24 O

Data terminal ready. Each DTRx can be set low by setting MCR0, modem control register bit 0 of its

associated ACE. DTRx

is cleared (high) by clearing the DTR bit (MCR0) or whenever a reset occurs.

When active (low), DTRx

indicates that its ACE is ready to receive data.

ENIRQ 43 59 I Parallel port interrupt source mode selection. When ENIRQ is low, the A T mode of interrupts is enabled.

In AT mode, INT2 is internally connected to ACK

. When ENIRQ is tied high, the PS-2 mode of interrupt

is enabled and INT2 is internally tied to the inverse of the PRINT

bit in the line printer status register.

INT2 is latched high on the rising edge of ACK

. INT2 is held until the status register is read, which then

clears the PRINT

status bit and INT2.

ERR 63 5 I Line printer error. ERR is an input line from the printer. The printer reports an error by holding ERR low

during the error condition.
GND 7, 27,5417, 43,

73

Ground (0 V). All terminals must be tied to GND for proper operation.

INIT 57 76 I/O Line printer initialize. INIT is an open-drain line that provides the printer with an active-low signal that

allows the printer initialization routine to be started. INIT

has an internal pullup resistor to VDD of

approximately 10 kΩ.
INT0, INT1 45, 60 64, 79 O External serial channel interrupt. Each serial channel interrupt 3-state output (enabled by bit 3 of the

MCR) goes active (high) when one of the following interrupts has an active (high) condition and is

enabled by the interrupt enable register of its associated channel: receiver error flag, received data

available, transmitter holding register empty , and modem status. The interrupt is cleared on appropriate

service. Upon reset, the interrupt output is in the high-impedance state.

TL16C552A, TL16C552AM

DUAL ASYNCHRONOUS COMMUNICATIONS ELEMENT

WITH FIFO

SLLS189D – NOVEMBER 1994 – REVISED JANUARY 1999

5

POST OFFICE BOX 655303 • DALLAS, TEXAS 75265

Terminal Functions (Continued)

TERMINAL

NO.

I/O

DESCRIPTION

NAME

FN PN

INT2 59 78 O Printer port interrupt. INT2 is an active-high, 3-state output generated by the positive transition of

ACK

. INT2 is enabled by bit 4 of the write control register. Upon reset, INT2 is in the high-impedance

state. Its mode is also controlled by ENIRQ

.

IOR 37 53 I Input/output read strobe. IOR is an active-low input that enables the selected channel to output data

to the data bus (DB0–DB7). The data output depends on the register selected by the address inputs
A0, A1, A2, and chip select. Chip select 0 (CS0

) selects ACE #1, chip select 1 (CS1) selects ACE #2,

and chip select 2 (CS2

) selects the printer port.

IOW 36 52 I Input/output write strobe. IOW is an active-low input causing data from the data bus to be input to either

ACE or to the parallel port. The destination depends on the register selected by the address inputs A0,
A1, A2, and chip selects CS0

, CS1, and CS2.
PD0–PD7 53–46 72–65 I/O Parallel data bits (0–7). PD0–PD7 provide a byte wide input or output port to the system.
PE 67 9 I Line printer paper empty. PE is an input line from the printer that goes high when the printer runs out

of paper.

PEMD 1 11 I Printer enhancement mode. When low, PEMD enables the write data register to the PD0–PD7 lines.

A high on PEMD allows direction control of the PD0–PD7 port by the DIR bit in the control register.
PEMD is usually tied low for the printer operation.

RESET 39 55 I Reset. When low, RESET forces the TL16C552A into an idle mode in which all serial data activities

are suspended. The modem control register and its associated outputs are cleared. The line status
register is cleared except for the transmitter holding register empty (THRE) and TEMT bits, which are
set. All functions of the device remain in an idle state until programmed to resume serial data activities.
RESET

has a hysteresis level of typically 400 mV .

RTS0,
RTS1

24, 12 37, 25 O Request to send. The RTS outputs are set low by setting MCR1 of its UARTs modem control register .

Both RTS

terminals are reset high by RESET. A low on RTS indicates that its ACE has data ready to

transmit. In half-duplex operations, RTS

controls the direction of the line.

RXRDY0,
RXRDY1

9, 61 19, 3 O

Receiver ready. Receiver direct memory access (DMA) signaling is also available through this output.
One of two types of DMA signaling can be selected using FCR3 when in FIFO mode. Only DMA mode
0 is allowed when in TL16C450 mode. For signal transfer DMA (a transfer is made between CPU bus
cycles), mode 0 is used. Multiple transfers that are made continuously until the receiver FIFO has been
emptied are supported by mode 1.

Mode 0. RXRDY is active (low) in FIFO mode (FCR0 = 1, FCR3 = 0) or in TL16C450 mode (FCR0 =

0) and the receiver FIFO or receiver holding register contains at least one character. When there are
no more characters in the FIFO or holding register, RXRDY

goes inactive (high).

Mode 1. RXRDY goes active (low) in the FIFO mode (FCR0 = 1) when FCR3 = 1 and the time-out or
trigger levels have been reached. RXRDY

goes inactive (high) when the FIFO or holding register is

empty.

RI0, RI1 30, 6 46, 16 I Ring indicator. The RI signal is a modem control input. Its condition is tested by reading MSR6 (RI) of

each ACE. The modem status register output TERI (MSR2) indicates whether RI

has changed from

high to low since the previous reading of the modem status register.

SIN0,
SIN1

41, 62 57, 4 I Serial data. SIN0 and SIN1 move information from the communication line or modem to the

TL16C552A receiver circuits. Mark is a high state and space is a low state. Data on serial data inputs

is disabled in loop mode.
SLCT 65 7 I Line printer select. SLCT is an input line from the printer that goes high when the printer is selected.
SLIN 58 77 I/O Line printer select. SLIN is an open-drain I/O that selects the printer when active (low). SLIN has an

internal pullup resistor to VDD of approximately 10 kΩ.

TL16C552A, TL16C552AM
DUAL ASYNCHRONOUS COMMUNICATIONS ELEMENT
WITH FIFO

SLLS189D – NOVEMBER 1994 – REVISED JANUARY 1999

6

POST OFFICE BOX 655303 • DALLAS, TEXAS 75265

Terminal Functions (Continued)

TERMINAL

NO.

I/O

DESCRIPTION

NAME

FN PN

SOUT0,
SOUT1

26, 10 39, 23 O Serial data outputs. SOUT0 and SOUT1 are the serial data outputs from the ACE transmitter circuitry.

A mark is a high state and a space is a low state. Each SOUT is held in the mark condition when the
transmitter is disabled (RESET

is asserted low), the transmitter register is empty, or when in the loop

mode.

STB 55 74 I/O Line printer strobe. STB provides communication between the TL16C552A and the printer. When STB

is active (low), it provides the printer with a signal to latch the data currently on the parallel port. STB
has an internal pullup resistor to VDD of approximately 10 kΩ.

TRI 2 12 I 3-state output control input. TRI controls the 3-state control of all I/O and output terminals. When TRI

is asserted, all I/Os and outputs are in the high-impedance state, allowing board level testers to drive
the outputs without overdriving internal buffers. TRI is level sensitive and is pulled down with an internal
resistor that is approximately 5 kΩ.

TXRDY0
TXRDY1

22, 42 35, 58 O Transmitter ready . T wo types of DMA signaling are available. Either can be selected using FCR3 when

operating in FIFO mode. Only DMA mode 0 is allowed when in TL16C450 mode. Single-transfer DMA
(a transfer is made between CPU bus cycles) is supported by mode 0. Multiple transfers that are made
continuously until the transmitter FIFO has been filled are supported by mode 1.

Mode 0. In FIFO mode (FCR0 = 1, FCR3 = 0) or in TL16C450 mode (FCR0 = 0) when there are no
characters in the transmitter holding register or transmitter FIFO, TXRDYx

is active (low). Once

TXRDYx

is activated (low), it goes inactive after the first character is loaded into the holding register

of the transmitter FIFO.
Mode 1. TXRDY goes active (low) in FIFO mode (FCR0 = 1) when FCR3 = 1 and there are no

characters in the transmitter FIFO. When the transmitter FIFO is completely full, TXRDY

goes inactive

(high).

V

DD

23, 40,646, 36,

56

Power supply. The VDD requirement is 5 V ±5%.

absolute maximum ratings over operating free-air temperature range (unless otherwise noted)

†

Supply voltage range, V

DD

(see Note 1) –0.5 V to VDD + 0.3 V. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

Input voltage range, V

I

–0.5 V to 7 V. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

Output voltage range, V

O

–0.5 V to VDD + 0.3 V. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

Continuous total power dissipation See Dissipation Rating Table. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

Operating free-air temperature range, T

A:

: I suffix –40°C to 85°C. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

M suffix –55°C to 125°C. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

Storage temperature range, T

stg

–65°C to 150°C. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

†

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.

DISSIPATION RATING TABLE‡

PACKAGE

TA ≤ 25°C

POWER RATING

DERATING FACTOR

§

ABOVE TA = 25°C

TA = 70°C

POWER RATING

TA = 125°C

POWER RATING

FN 1730 mW 19.2 mW/°C 865 mW –
HV 1689 mW 13.5 mW/°C 1081 mW 337 mW

‡

Power ratings assume a maximum junction temperature (TJ) of 115°C for ’I’ and 150°C for ’M’ suffix devices.

§

Derating factor is the inverse of the junction-to-ambient thermal resistance, R

θJA

.

TL16C552A, TL16C552AM

DUAL ASYNCHRONOUS COMMUNICATIONS ELEMENT

WITH FIFO

SLLS189D – NOVEMBER 1994 – REVISED JANUARY 1999

7

POST OFFICE BOX 655303 • DALLAS, TEXAS 75265

recommended operating conditions

MIN NOM MAX UNIT

Supply voltage, V

DD

4.75 5 5.25 V

Clock high-level input voltage, V

IH(CLK)

2 V

DD

V

Clock low-level input voltage, V

IL(CLK)

0 0.8 V

High-level input voltage, V

IH

2 V

DD

V

Low-level input voltage, V

IL

0 0.8 V

Clock frequency, f

clock

16 MHz

p

p

I suffix –40 85

°

Operating free-air temperature, T

A

M suffix –55 125

°C

package thermal characteristics

FN Package HV Package

PARAMETER

TEST CONDITIONS

MIN TYP MAX MIN TYP MAX

UNIT

R

θJA

Junction-to-ambient thermal impedance Board mounted, no air flow 52 74 °C/W

R

θJC

Junction-to-case thermal impedance 14 3 °C/W

T

J

Junction temperature 115 150 °C/W

electrical characteristics over recommended ranges of operating free-air temperature and supply
voltage (unless otherwise noted)

PARAMETER TEST CONDITIONS MIN MAX UNIT

V

OH

High-level output voltage

IOH = –12 mA for PD0–PD7,
IOH = –4 mA for all other outputs (see Note 2),

2.4 V

V

OL

Low-level output voltage

IOL = 12 mA for PD0–PD7,
IOL = 12 mA for INIT

, AFD, STB, and SLIN,

IOL = 4 mA for all other outputs

0.4 V

I

I

Input current

VDD = 5.25 V (see Note 3),
All other terminals are floating

±10 µA

I

I(CLK)

Clock input current VI = 0 to 5.25 V ±10 µA

p

I

High-impedance output current

V

DD

= 5.25 V,

V

O

= 0

with chi deselected or

±20

µ

A

IOZHigh im edance out ut current

V

O

=

5.25 V with chi

p and write mode selected (see Note

2)

±20

µA

pp

V

DD

= 5.25 V,

No load

s on outputs,

IDDSupply current

DD

p

50

mA

In uts at 0.8 V or 2 V

,

f

clock

= 8

MHz

NOTES: 2. Excluding INIT , AFD, STB, and SLIN. They are open-drain terminals with an internal pullup resistor to VDD of approximately 10 KΩ.

3. Excluding the TRI input terminal. It contains an internal pulldown resistor of approximately 5 kΩ.

clock timing requirements over recommended ranges of operating free-air temperature and supply
voltage

MIN MAX UNIT

t

w1

Pulse duration, CLK ↑ (external clock) (see Figure 1) 31 ns

t

w2

Pulse duration, CLK ↓ (external clock) (see Figure 1) 31 ns

t

w3

Pulse duration, RESET 1000 ns

TL16C552A, TL16C552AM
DUAL ASYNCHRONOUS COMMUNICATIONS ELEMENT
WITH FIFO

SLLS189D – NOVEMBER 1994 – REVISED JANUARY 1999

8

POST OFFICE BOX 655303 • DALLAS, TEXAS 75265

read cycle timing requirements over recommended ranges of operating free-air temperature and
supply voltage (see Note 4 and Figure 4)

MIN MAX UNIT

t

w4

Pulse duration, IOR ↓ 80 ns

t

su1

Setup time, CSx valid before IOR ↓ (see Note 5) 15 ns

t

su2

Setup time, A2–A0 valid before IOR ↓ (see Note 5) 15 ns

t

h1

Hold time, A2–A0 valid after IOR ↑ (see Note 5) 20 ns

t

h2

Hold time, CSx valid after IOR ↑ (see Note 5) 20 ns

t

d1

Delay time, t

su2

+ tw4 + td2 (see Note 6) 175 ns

t

d2

Delay time, IOR ↑ to IOR or IOW ↓ 80 ns

NOTES: 4. These parameters are not production tested.

5. The internal address strobe is always active.

6. In 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 Note 7 and Figure 5)

MIN MAX UNIT

t

w5

Pulse duration, IOW ↓ 80 ns

t

su4

Setup time, CSx valid before IOW ↓ (see Note 8) 15 ns

t

su5

Setup time, A2–A0 valid before IOW ↓ (see Note 8) 15 ns

t

su6

Setup time, DB0–DB7 valid before IOW ↑ 15 ns

t

h3

Hold time, A2–A0 valid after IOW ↑ (see Note 8) 20 ns

t

h4

Hold time, CSx valid after IOW ↑ (see Note 8) 20 ns

t

h5

Hold time, DB0–DB7 valid after IOW ↑ 15 ns

t

d3

Delay time, t

su5

+ tw5 + t

d4

175 ns

t

d4

Delay time, IOW ↑ to IOW or IOR ↓ 80 ns

NOTES: 7. These parameters are not production tested.

8. 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 9 and Figure 4)

PARAMETER MIN MAX UNIT

t

pd1

Propagation delay time from IOR ↓ to BDO ↑ or from IOR ↑ to BDO ↓ 60 ns

t

en

Enable time from IOR ↓ to DB0–DB7 valid (see Note 10) 60 ns

t

dis

Disable time from IOR ↑ to DB0–DB7 released (see Note 10) 60 ns

NOTES: 9. These parameters are not production tested.

10. VOL and VOH (and the external loading) determine the charge and discharge time.

TL16C552A, TL16C552AM

DUAL ASYNCHRONOUS COMMUNICATIONS ELEMENT

WITH FIFO

SLLS189D – NOVEMBER 1994 – REVISED JANUARY 1999

9

POST OFFICE BOX 655303 • DALLAS, TEXAS 75265

transmitter switching characteristics over recommended ranges of operating free-air temperature
and supply voltage (see Note 11 and Figures 6, 7, and 8)

PARAMETER TEST CONDITIONS MIN MAX UNIT

t

d5

Delay time, interrupt THRE ↓ to SOUT ↓ at start See Figure 6 8 24

RCLK
cycles

t

d6

Delay time, SOUT ↓ at start to interrupt THRE ↑ See Note 12 and Figure 6 8 9

RCLK
cycles

t

d7

Delay time, IOW (WR THR) ↑ to interrupt THRE ↑ See Note 12 and Figure 6 16 32

RCLK
cycles

t

d8

Delay time, SOUT ↓ at start to TXRDY ↓

CL = 100 pF,
See Figures 7 and 8

8

RCLK
cycles

t

pd2

Propagation delay time from IOW (WR THR) ↓ to interrupt THRE ↓

CL = 100 pF,
See Figure 6

140 ns

t

pd4

Propagation delay time from IOR (RD IIR) ↑ to interrupt THRE ↓

CL = 100 pF,
See Figure 6

140 ns

t

pd5

Propagation delay time from IOW (WR THR) ↑ to TXRDY ↑

CL = 100 pF,
See Figures 7 and 8

195 ns

NOTES: 11. These parameters are not production tested.

12. When 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 Note 13 and Figures 9 through 13)

PARAMETER TEST CONDITIONS MIN MAX UNIT

t

d9

Delay time from stop to INT ↑ See Note 14 1

RCLK

cycle

t

pd6

Propagation delay time from RCLK ↑ to sample CLK ↑ 100 ns

t

pd7

Propagation delay time from IOR (RD RBR/RD LSR) ↓ to reset interrupt ↓ CL = 100 pF 150 ns

t

pd8

Propagation delay time from IOR (RD RBR) ↓ to RXRDY ↑ 150 ns

NOTES: 13. These parameters are not production tested.

14. The receiver data available indicator, the overrun error indicator, the trigger level interrupts, and the active RXRDY

indicator are
delayed three RCLK cycles in 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 RDRBR goes active.
There are eight RCLK cycle delays for trigger change level interrupts.

modem control switching characteristics over recommended ranges of operating free-air
temperature and supply voltage, C

L

= 100 pF (see Note 15 and Figure 14)

PARAMETER MIN MAX UNIT

t

pd9

Propagation delay time from IOW (WR MCR) ↑ to RTS (DTR) ↓↑ 100 ns

t

pd10

Propagation delay time from modem input (CTS, DSR) ↓↑ to interrupt ↑ 170 ns

t

pd11

Propagation delay time from IOR (RD MSR) ↑ to interrupt ↓ 140 ns

t

pd12

Propagation delay time from RI ↑ to interrupt ↑ 170 ns

NOTE 15: These parameters are not production tested.

TL16C552A, TL16C552AM
DUAL ASYNCHRONOUS COMMUNICATIONS ELEMENT
WITH FIFO

SLLS189D – NOVEMBER 1994 – REVISED JANUARY 1999

10

POST OFFICE BOX 655303 • DALLAS, TEXAS 75265

parallel port timing requirements over recommended ranges of supply voltage and operating
free-air temperature (see Note 16 and Figures 15, 16, and 17)

MIN MAX UNIT

t

su7

Setup time, data valid before STB ↓ 1 µs

t

h6

Hold time, data valid after STB ↑ 1 µs

t

w6

Pulse duration, STB ↓ 1 µs

t

d10

Delay time, BUSY ↑ to ACK ↓ Defined by printer

t

d11

Delay time, BUSY ↓ to ACK ↓ Defined by printer

t

w7

Pulse duration, BUSY ↑ Defined by printer

t

w8

Pulse duration, ACK ↓ Defined by printer

t

d12

Delay time, BUSY ↑ after STB ↑ Defined by printer

t

d13

Delay time, INT2 ↓ after ACK ↓ (see Note 17) 22 ns

t

d14

Delay time, INT2 ↑ after ACK ↑ (see Note 17) 20 ns

t

d15

Delay time, INT2 ↑ after ACK ↑ (see Note 17) 24 ns

t

d16

Delay time, INT2 ↓ after IOR ↑ (see Note 17) 25 ns

NOTES: 16. These parameters are not production tested.

17. t

d13–td16

are all measured with a 15-pF load.

PARAMETER MEASUREMENT INFORMATION

2 V

0.8 V

CLK (XTAL1)

t

w1

t

w2

f

clock

= 16 MHz MAX

2 V

0.8 V

Figure 1. CLK Voltage Waveform

Device Under Test

680 Ω

82 pF
(see Note A)

2.54 V

TL16C552A

NOTE A: This includes scope and jig capacitance.

Figure 2. Output Load Circuit

TL16C552A, TL16C552AM

DUAL ASYNCHRONOUS COMMUNICATIONS ELEMENT

WITH FIFO

SLLS189D – NOVEMBER 1994 – REVISED JANUARY 1999

11

POST OFFICE BOX 655303 • DALLAS, TEXAS 75265

PARAMETER MEASUREMENT INFORMATION

Option

Jumpers

Data Bus

Address Bus

Control Bus

9-Pin D Connector

9-Pin D Connector

25-Pin D Connector

Serial

Channel 1

Buffers

Serial

Channel 2

Buffers

Parallel

Port

R/C

Network

Dual

ACE and

Printer

Port

TL16C552A

Figure 3. Basic Test Configuration

Valid

Valid

t

h1

t

su1

t

su2

t

h2

t

d1

t

d2

t

w4

t

pd1

t

pd1

t

dis

t

en

Valid Data

A2, A1, A0

CS0

, CS1, CS2

IOR

IOW

BDO

DB0–DB7

Active

Active

Active

50% 50%

50% 50%

50% 50%

50%

50% 50%

50%

or

Figure 4. Read Cycle Timing Waveforms

TL16C552A, TL16C552AM
DUAL ASYNCHRONOUS COMMUNICATIONS ELEMENT
WITH FIFO

SLLS189D – NOVEMBER 1994 – REVISED JANUARY 1999

12

POST OFFICE BOX 655303 • DALLAS, TEXAS 75265

PARAMETER MEASUREMENT INFORMATION

Valid

Valid

t

h3

t

su4

t

su5

t

h4

t

d3

t

d4

t

w5

A2, A1, A0

CS0, CS1, CS2

IOW

IOR

Active

Active

t

h5

t

su6

Valid Data

Active

DB0–DB7

50% 50%

50% 50%

50% 50%

50%

50%

or

Figure 5. Write Cycle Timing Waveforms

Start

Data Bits 5–8

Parity

Stop (1–2)

Start

Serial Out

(SOUT)

Interrupt

(THRE)

IOW

(WR THR)

IOR

(RD IIR)

t

d5

t

d6

t

pd2

t

pd4

t

pd2

t

d7

50%

50%

50% 50% 50%

50%

50%

50%

50%50%

50%

Figure 6. Transmitter Timing Waveforms

IOW

(WR THR)

t

d8

t

pd5

SOUT

TXRDY

Byte #1

ParityData Stop

Start

50%

50%

50%

50%

Figure 7. Transmitter Ready Mode 0 Timing Waveforms

TL16C552A, TL16C552AM

DUAL ASYNCHRONOUS COMMUNICATIONS ELEMENT

WITH FIFO

SLLS189D – NOVEMBER 1994 – REVISED JANUARY 1999

13

POST OFFICE BOX 655303 • DALLAS, TEXAS 75265

PARAMETER MEASUREMENT INFORMATION

IOW

(WR THR)

t

d8

t

pd5

SOUT

TXRDY

Byte #16

ParityData Stop

Start

Start of
Byte #16

FIFO Full

50%

50% 50%

Figure 8. Transmitter Ready Mode 1 Timing Waveforms

ParityData Bits 5–8

Stop

Start

t

pd6

t

d9

RCLK

CLK

TL16C450 Mode

SIN

(receiver input

data)

Sample

CLK

Interrupt

(data ready or

RCVR ERR)

IOR

Active

t

pd7

50%

50%

50%

8 CLK Cycles

Figure 9. Receiver Timing Waveforms

TL16C552A, TL16C552AM
DUAL ASYNCHRONOUS COMMUNICATIONS ELEMENT
WITH FIFO

SLLS189D – NOVEMBER 1994 – REVISED JANUARY 1999

14

POST OFFICE BOX 655303 • DALLAS, TEXAS 75265

PARAMETER MEASUREMENT INFORMATION

Trigger

Interrupt

(FCR6, 7=0, 0)

Active

ParityData Bits 5–8

Stop

Start

Active

t

pd7

t

d9

SIN

Sample

CLK

IOR

(RD LSR)

LSI

Interrupt

IOR

(RD RBR)

(FIFO at or above
trigger level)

(FIFO below
trigger level)

t

pd7

50%

50%

50%

50%

50%

50%

Figure 10. Receiver FIFO First Byte (Sets RDR) Waveforms

ActiveActive

Top Byte of FIFO

IOR

(RD LSR)

CLK

Sample

SIN

Active

Time Out or

Trigger Level

Interrupt

LSI

Interrupt

IOR

(RD RBR)

(FIFO at or above
trigger level)

(FIFO below
trigger level)

Previous Byte

Read From FIFO

Stop

t

d9

(see Note A)

t

pd7

t

d9

t

pd7

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

TL16C552A, TL16C552AM

DUAL ASYNCHRONOUS COMMUNICATIONS ELEMENT

WITH FIFO

SLLS189D – NOVEMBER 1994 – REVISED JANUARY 1999

15

POST OFFICE BOX 655303 • DALLAS, TEXAS 75265

PARAMETER MEASUREMENT INFORMATION

Active

IOR

(RD RBR)

CLK

Sample

SIN

(first byte)

Stop

t

d9

(see Note B )

RXRDY

t

pd8

(see Note A)

50%

50%

50%

NOTES: A. This is the reading of the last byte in the FIFO.

B. If FCR0 = 1, td9 = 3 RCLK cycles. For a time-out interrupt, td9 = 8 RCLK cycles.

Figure 12. Receiver Ready Mode 0 Waveforms

Active

IOR

(RD RBR)

CLK

Sample

Stop

t

d9

(see Note B)

RXRDY

t

pd8

SIN

(first byte that reaches

the trigger level)

(see Note A)

50%

50%

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 Waveforms

TL16C552A, TL16C552AM
DUAL ASYNCHRONOUS COMMUNICATIONS ELEMENT
WITH FIFO

SLLS189D – NOVEMBER 1994 – REVISED JANUARY 1999

16

POST OFFICE BOX 655303 • DALLAS, TEXAS 75265

PARAMETER MEASUREMENT INFORMATION

IOW

(WR MCR)

RTS

, DTR

CTS, DSR, DCD

INT0, INT1,
1 INT, 2 INT

IOR

(RD MSR)

RI

t

pd9

t

pd9

t

pd10

t

pd11

t

pd10

t

pd12

50% 50%

50%50%

50% 50% 50% 50%

50%

50%

50%50%

Figure 14. Modem Control Timing Waveforms

ACK

BUSY

t

su7

STB

DATA

Valid

t

d10

t

h6

t

w8

t

d11

t

w7

t

d12

t

w6

50%

50%

50% 50%

50%50%

50% 50% 50%

Figure 15. Parallel Port Timing Waveforms

TL16C552A, TL16C552AM

DUAL ASYNCHRONOUS COMMUNICATIONS ELEMENT

WITH FIFO

SLLS189D – NOVEMBER 1994 – REVISED JANUARY 1999

17

POST OFFICE BOX 655303 • DALLAS, TEXAS 75265

PARAMETER MEASUREMENT INFORMATION

IOR

(RD_LPS)

Line Printer

Status Register,

Bit 2 (PRINT

)

t

d13

t

d(int

(see Note A)

ACK

ENIRQ

INT2

t

d14

50%

50%

50%50%

50%

50%

NOTE A: A timing value is not provided for t

d(int)

in the tables because the line printer status register, bit 2 (PRINT

) is an internal signal.

Figure 16. Parallel Port AT Mode Timing (ENIRQ = Low) Waveforms

IOR

(RD_LPS)

PRINT

t

d15

t

d16

ACK

ENIRQ

INT2

50%

50%

50%

50%

Figure 17. Parallel Port PS/2 Mode Timing (ENIRQ = High) Waveforms

RESET

t

w3

50%50%

Figure 18. RESET Voltage Waveform

TL16C552A, TL16C552AM
DUAL ASYNCHRONOUS COMMUNICATIONS ELEMENT
WITH FIFO

SLLS189D – NOVEMBER 1994 – REVISED JANUARY 1999

18

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 internal registers are shown in Table 1.

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

The address, read, and write inputs are used with the divisor latch access bit (DLAB) in the line control register (bit 7)
to select the register to be written to or read from (see Table 2). Individual bits within the registers are referred to by
the register mnemonic and the bit number in parenthesis. As an example, LCR7 refers to line control register bit 7.

The transmitter holding register and receiver buffer register are data registers that hold from five to eight bits of data.
If fewer 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 (TL16C450 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.

Table 2. Register Selection

†

DLAB A2 A1 A0 MNEMONIC REGISTER

L L L L RBR Receiver buffer register (read only)
L L L L THR Transmitter holding register (write only)

L L L H IER Interrupt enable register
X L H L IIR Interrupt identification register (read only)
X L H L FCR FIFO control register (write only)
X L H H LCR Line control register
X H L L MCR Modem control register
X H L H LSR Line status register
X H H L MSR Modem status register
X H H H SCR Scratch pad register
H L L L DLL LSB divisor latch
H L L H DLM MSB divisor latch

†

The serial channel is accessed when either CS0

or CS1 is low.

X = irrelevant, L = low level, H = high level

TL16C552A, TL16C552AM

DUAL ASYNCHRONOUS COMMUNICATIONS ELEMENT

WITH FIFO

SLLS189D – NOVEMBER 1994 – REVISED JANUARY 1999

19

POST OFFICE BOX 655303 • DALLAS, TEXAS 75265

PRINCIPLES OF OPERATION

accessible registers

Using the CPU, the system programmer 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.

T able 3. Summary of Accessible Registers

REGISTER

REGISTER BIT NUMBER

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 Data Data Data Data Data Data Data Data

(write only) Bit 7 Bit 6 Bit 5 Bit 4 Bit 3 Bit 2 Bit 1 Bit 0

0

†

DLL Bit 7 Bit 6 Bit 5 Bit 4 Bit 3 Bit 2 Bit 1 Bit 0

1

†

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 (ERLSI

)

(

ETBEI

)

(

ERBFI

)

1

IER0000

(EDSSI) Enable

modem status

(ERLSI)

Enable

(ETBEI)

Enable

(ERBFI)

Enable

modem status

interrupt

Enable

receiver line

Enable

transmitter

Enable

received

status holding data

interrupt

g

register available

g

empty interrupt

interrupt

2

FCR

Receiver

Receiver

Reserved

Reserved

DMA

Transmitter

Receiver

FIFO

(writ

e only

)

tri

gger

(MSB)

tri

gger

(LSB)

mode selec

t

FIFO

rese

t

FIFO

rese

t

enable

2 IIR FIFOs

FIFOs

0 0 Interrupt ID

Interrupt ID Interrupt ID 0 if

(read only) enabled

‡

enabled

‡

bit 3

‡

bit 2 bit 1 interrupt

pending

3 LCR (DLAB) Set Stick (EPS) (PEN) (STB) (WLSB1) (WLSB0)

()

Divisor latch break parity

()

Even parity

()

Parity enable

()

Number of

()

Word length

()

Word length

access bit select stop bits select bit 1 select bit 0

4 MCR 0 0 0 Loop OUT2 Enable OUT1 (RTS) (DTR)

external (an unused

()

Request

()

Data

interrupt

internal

to send terminal

(INT

0 or

INT1)

signa

l)

ready

5 LSR Error in (TEMT) (THRE) (BI) (FE) (PE) (OE) (DR)

receiver

()

Transmitter

()

Transmitter

()

Break

()

Framing

()

Parity

()

Overrun

()

Data

FIFO

‡

empty holding

interrupt error error error ready

register

p

empty

6

MSR

(DCD)

(RI)

(DSR)

(CTS)

(∆DCD)

(TERI)

(∆DSR)

(∆CTS)

Data carrier

Ring

Data set

Clear

Delta data

Trailing edge

Delta data

Delta clear

detect

indicator

ready

to send

carrier detect

ring indicator

set ready

clear to send

7 SCR Bit 7 Bit 6 Bit 5 Bit 4 Bit 3 Bit 2 Bit 1 Bit 0

†

DLAB = 1

‡

These bits are always 0 when FIFOs are disabled.

TL16C552A, TL16C552AM
DUAL ASYNCHRONOUS COMMUNICATIONS ELEMENT
WITH FIFO

SLLS189D – NOVEMBER 1994 – REVISED JANUARY 1999

20

POST OFFICE BOX 655303 • DALLAS, TEXAS 75265

PRINCIPLES OF OPERATION

FIFO control register (FCR)

This write-only register is at the same location as the interrupt identification register. It enables and clears the
FIFOs, sets the trigger level of the receiver FIFO, and selects the type of DMA signaling.

D

Bit 0: FCR0 enables both the transmitter 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 and vice versa. Programming of other FCR bits is enabled by setting FCR0.

D

Bit 1: When set, FCR1 clears all bytes in the receiver FIFO and resets the counter. This does not clear the
shift register.

D

Bit 2: When set, FCR2 clears all bytes in the transmitter FIFO and resets the counter. This does not clear
the shift register.

D

Bit 3: When set, FCR3 changes the RXRDY and TXRDY terminals from mode 0 to mode 1 when FCR0
is set.

D

Bits 4 and 5: FCR4 and FCR5 are reserved for future use.

D

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

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 received 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. When 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.

TL16C552A, TL16C552AM

DUAL ASYNCHRONOUS COMMUNICATIONS ELEMENT

WITH FIFO

SLLS189D – NOVEMBER 1994 – REVISED JANUARY 1999

21

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. The last received serial character is longer than four previous continuous-character times (if two stop

bits are programmed, the second one is included in the time delay).

c. The last CPU read of the FIFO is more than four previous continuous-character times. 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.1

2. By using the RCLK 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 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.

Transmitter interrupts occur as follows when the transmitter and transmitter 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 when the
following occurs:

THRE = 1 and there is not a minimum of two bytes at the same time in transmitter FIFO since the last
THRE = 1. The first transmitter interrupt after changing FCR0 is immediate, assuming it is enabled.

Receiver FIFO trigger level and character time-out interrupts have the same priority as the received 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 with FCR0 = 1 puts the ACE into the FIFO polled mode. The receiver
and transmitter are controlled separately. Either one 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 transmitter 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 (INT0 or
INT1) output. All interrupts are disabled by clearing IER0 – IER3. Interrupts are enabled by setting the
appropriate bits of the IER. Disabling the interrupt system inhibits the interrupt identification register and the
active (high) interrupt output. All other system functions operate in their normal manner, including the setting
of the LSRs and MSRs. The contents of the IER shown in Table 3 are described in the following bulleted list.

D

Bit 0: When IER0 is set, IER0 enables the received data available interrupt and the time-out interrupts in
the FIFO mode.

TL16C552A, TL16C552AM
DUAL ASYNCHRONOUS COMMUNICATIONS ELEMENT
WITH FIFO

SLLS189D – NOVEMBER 1994 – REVISED JANUARY 1999

22

POST OFFICE BOX 655303 • DALLAS, TEXAS 75265

PRINCIPLES OF OPERATION

interrupt enable register (IER) (continued)

D

Bit 1: When IER1 is set, the transmitter holding register empty interrupt is enabled.

D

Bit 2: When IER2 is set, the receiver line status interrupt is enabled.

D

Bit 3: When IER3 is set, the modem status interrupt is enabled.

D

Bits 4 – 7: IER4 through IER7 are cleared.

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

Priority 1–Receiver line status (highest priority)

D

Priority 2–Receiver data ready or receiver character time out

D

Priority 3–Transmitter holding register empty

D

Priority 4–Modem status (lowest priority)

Information indicating that a prioritized interrupt is pending and the type of interrupt 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 None None None None
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 MSR read

D

Bit 0: IIR0 indicates whether an interrupt is pending. When IIR0 is cleared, an interrupt is pending.

D

Bits 1 and 2: IIR1 and IIR2 identify the highest priority interrupt pending, as indicated in Table 5.

D

Bit 3: IIR3 is always cleared in TL16C450 mode. This bit is set along with bit 2 in FIFO mode and when a
trigger change level interrupt is pending.

D

Bits 4 and 5: IIR4 and IIR5 are always cleared.

D

Bits 6 and 7: IIR6 and IIR7 are set when FCR0 = 1.

TL16C552A, TL16C552AM

DUAL ASYNCHRONOUS COMMUNICATIONS ELEMENT

WITH FIFO

SLLS189D – NOVEMBER 1994 – REVISED JANUARY 1999

23

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PRINCIPLES OF OPERATION

line control register (LCR)

The format of the data character is controlled by the LCR. The LCR can be read. Its contents are described in
the following bulleted list and shown in Figure 19.

D

Bits 0 and 1: LCR0 and LCR1 are the word length select bits. The number of bits in each serial character
is programmed as shown.

D

Bit 2: LCR2 is the stop bit select bit. LCR2 specifies the number of stop bits in each transmitted character.
The receiver always checks for one stop bit.

D

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.

D

Bit 4: LCR4 is the even parity select bit. When LCR4 is set, even parity is enabled.

D

Bit 5: LCR5 is the stick parity bit. When parity is enabled (LCR3 = 1), LCR5 = 1 causes the transmission
and reception of a parity bit to be 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.

D

Bit 6: LCR6 is the break control bit. When LCR6 is set, the serial output (SOUT1/SOUT0) is forced to the
spacing state (low). The break control bit acts only on the serial output and does not affect the transmitter
logic. When 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 high (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. LCR7 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.

TL16C552A, TL16C552AM
DUAL ASYNCHRONOUS COMMUNICATIONS ELEMENT
WITH FIFO

SLLS189D – NOVEMBER 1994 – REVISED JANUARY 1999

24

POST OFFICE BOX 655303 • DALLAS, TEXAS 75265

PRINCIPLES OF OPERATION

line control register (LCR) (continued)

LCR7LCR6LCR5LCR4LCR3LCR2LCR1LCR

0

Line Control Register

Word Length
Select

Stop Bit
Select

Parity Enable

Even Parity
Select

Stick Parity

Break Control

Divisor Latch
Access Bit

0 0 = 5 Data Bits
0 1 = 6 Data Bits
1 0 = 7 Data Bits
1 1 = 8 Data Bits

0 = 1 Stop Bits
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 19. Line Control Register Contents

line printer port

The line printer port contains the functionality of the port included in the TL16C452 but offers a hardware
programmable extended mode controlled by the printer enhancement mode (PE) terminal. This enhancement
is the addition of a direction control bit and an interrupt status bit.

register 0 line printer data register

The line printer (LPT) port is either output only or bidirectional depending on the state of the extended mode
terminal and data direction control bits.

Compatibility mode (PEMD = L)

Reads to the LPT data register and returns the last data that was written to the port. Write operations
immediately output data to PD0–PD7.

Extended mode (PEMD = H)

Read operations return either the data last written to the LPT data register when the direction bit is cleared or
return the data that is present on PD0 – PD7 when the direction is set to read. Write operations to the LPT
data register latch data into the output register; however, they only drive the LPT port when the direction bit is
cleared.

TL16C552A, TL16C552AM

DUAL ASYNCHRONOUS COMMUNICATIONS ELEMENT

WITH FIFO

SLLS189D – NOVEMBER 1994 – REVISED JANUARY 1999

25

POST OFFICE BOX 655303 • DALLAS, TEXAS 75265

PRINCIPLES OF OPERATION

line printer port (continued)

Table 6 summarizes the configuration of the PD port based on the combinations of the logic level on the
PEMD terminal and the value of the direction control bit (DIR).

Table 6. Extended Mode and Direction Control Bit Combinations

PEMD DIR PD0–PD7 FUNCTION

L X PC/AT mode – output
H 0 PS/2 mode – output
H 1 PS/2 mode – input

register 1 read line printer status register

The line printer status (LPS) register is a read-only register that contains interrupt and printer status of the LPT
connector terminals. Table 7 (in the default column) shows the values of each bit after reset in the case of the
printer being disconnected from the port.

Table 7. LPS Register Bit Description

BIT DESCRIPTION DEFAULT

0 Reserved 1
1 Reserved 1
2 PRINT 1
3 ERR †
4 SLCT †
5 PE †
6 ACK †
7 BSY †

†

Outputs are dependent upon device inputs.

D

Bits 0 and 1: LPS0 and LPS1 are reserved and always set.

D

Bit 2: LPS2 is the printer interrupt (PRINT, active low) status bit. When cleared, LPS2 indicates that the
printer has acknowledged the previous transfer with an ACK handshake (if bit 4 of the control register is set).
The bit is cleared on the active-to-inactive transition of the ACK

signal. This bit is set after a read of the status

port.

D

Bit 3: ERR is the error status bit and corresponds to ERR input.

D

Bit 4: SLCT is the select status bit and corresponds to SLCT input.

D

Bit 5: PE is the paper empty status bit and corresponds to PE input.

D

Bit 6: ACK is the acknowledge status bit corresponds to ACK input.

D

Bit 7: BSY is the busy status bit and corresponds to BUSY input (active high).

TL16C552A, TL16C552AM
DUAL ASYNCHRONOUS COMMUNICATIONS ELEMENT
WITH FIFO

SLLS189D – NOVEMBER 1994 – REVISED JANUARY 1999

26

POST OFFICE BOX 655303 • DALLAS, TEXAS 75265

PRINCIPLES OF OPERATION

register 2 line printer control register

The line printer control (LPC) register is a read/write port that controls the PD0–PD7 direction and drives the
printer control lines. Write operations set or clear these bits, whereas read operations return the state of the last
write operation to this register. The bits in this register are defined in Table 8 and the following bulleted list.

Table 8. LPC Register Bit Description

BIT DESCRIPTION

0 STB
1 AFD
2 INIT
3 SLIN
4 INT2 EN
5 DIR
6 Reserved 0
7 Reserved 0

D

Bit 0: STB is the printer strobe control bit. When STB is set, the STB signal is asserted on the LPT interface.
When STB is cleared, the STB

signal is negated.

D

Bit 1: AFD is the autofeed control bit. When AFD is set, the AFD signal is asserted on the LPT interface.
When AFD is cleared, the signal is negated.

D

Bit 2: INIT is the initialize printer control bit. When INIT is set, the INIT signal is negated. When INIT is
cleared, the INIT

signal is asserted on the LPT interface.

D

Bit 3: SLIN is the select input control bit. When SLIN is set, the SLIN signal is asserted on the LPT interface.
When SLIN is cleared, the signal is negated.

D

Bit 4: INT2 EN is the interrupt request enable control bit. When set, INT2 EN enables interrupts from the
LPT port. When cleared, INT2 EN disables interrupts and places INT2 signal in the high-impedance state.

D

Bit 5: DIR is the direction control bit which is only used when PEMD is high. When DIR is set, the output
buffers in the LPD port are disableded to allow data driven from external sources to be read from the LPD
port. When DIR is cleared, the LPD port is in the output mode.

D

Bits 6 and 7: These bits are reserved and are always cleared.

TL16C552A, TL16C552AM

DUAL ASYNCHRONOUS COMMUNICATIONS ELEMENT

WITH FIFO

SLLS189D – NOVEMBER 1994 – REVISED JANUARY 1999

27

POST OFFICE BOX 655303 • DALLAS, TEXAS 75265

PRINCIPLES OF OPERATION

line status register (LSR)

The LSR is a single register that provides status indicators. The LSR bits shown in T able 9 are described in the
following bulleted list.

D

Bit 0: DR is the data ready bit. When set, an incoming character is received and transferred into the receiver
buffer register or in the FIFO. LSR0 is cleared by a CPU read of the data in the receiver buffer register or
in the FIFO.

D

Bit 1: OE is the overrun error bit. An OE 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 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.

D

Bit 2: PE is the parity error bit. A PE 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 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.

D

Bit 3: FE is the framing error bit. An FE 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 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

Bit 4: BI is the break interrupt bit. BI 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 FIFO mode, this is associated with a particular
character in the FIFO. LSR4 reflects 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: THRE is the transmitter holding register empty 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 into the transmitter shift register. LSR5 is cleared by the loading of the transmitter holding
register by the CPU. LSR5 is not cleared by a CPU read of the LSR. In FIFO mode when the transmitter
FIFO is empty , this bit is set. It is cleared when one byte is written to the transmitter 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.

D

Bit 6: TEMT is the transmitter empty bit. TEMT is set when the transmitter holding register (THR) and the
transmitter shift register are both empty. LSR6 is cleared when a character is loaded into the THR and
remains cleared until the character is transferred out of SOUT. TEMT is not cleared by a CPU read of the
LSR. In FIFO mode, when both the transmitter FIFO and shift register are empty, TEMT is set.

D

Bit 7: LSR7 is the receiver FIFO error bit. The LSR7 bit is always cleared in TL16C450 mode. In FIFO mode,
it is set when at least one of the following data errors occurs 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.

TL16C552A, TL16C552AM
DUAL ASYNCHRONOUS COMMUNICATIONS ELEMENT
WITH FIFO

SLLS189D – NOVEMBER 1994 – REVISED JANUARY 1999

28

POST OFFICE BOX 655303 • DALLAS, TEXAS 75265

PRINCIPLES OF OPERATION

line status register (LSR) (continued)

NOTE:

The LSR may be written to. However, this function is intended only for factory test. It should be
considered as read only by applications software.

Table 9. 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 empty (TEMT) Empty Not empty
LSR7 receiver FIFO error Error in FIFO No error in FIFO

master reset

After power up, the ACE RESET input should be held low for one microsecond to reset the ACE circuits to an
idle mode until initialization. A low on RESET

causes the following:

D

It initializes the transmitter and receiver clock counters.

D

It clears the LSR except for transmitter shift 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, receiver buffer register, and transmitter holding buffer register are not affected.

Following the removal of the reset condition (RESET

high), the ACE remains in idle mode until programmed.
A hardware reset of the ACE sets the THRE and TEMT status bit 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 10.

TL16C552A, TL16C552AM

DUAL ASYNCHRONOUS COMMUNICATIONS ELEMENT

WITH FIFO

SLLS189D – NOVEMBER 1994 – REVISED JANUARY 1999

29

POST OFFICE BOX 655303 • DALLAS, TEXAS 75265

PRINCIPLES OF OPERATION

master reset (continued)

Table 10. RESET Effects on Registers and Signals

REGISTER/SIGNAL RESET CONTROL RESET

Interrupt enable register Reset All bits cleared (0–3 forced and 4–7 permanent)

p

Bit 0 is set, bits 1, 2, 3, 6, and 7 are cleared, and bits 4–5 are permanently

Interrupt identification register

Reset

, ,,,, , y

cleared.
Line control register Reset All bits are cleared.
Modem control register Reset All bits are cleared (5–7 permanently).
FIFO control register Reset All bits are cleared.
Line status register Reset All bits are cleared, except bits 5 and 6 are set.
Modem status register Reset Bits 0–3 are cleared, bits 4–7 input signal.
SOUT Reset High
Interrupt (RCVR errors) 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
OUT2 Reset High
RTS Reset High
DTR Reset High
OUT1 Reset High

modem control register (MCR)

The MCR controls the interface with the modem or data set as described in Figure 20. MCR can be written to
and read from. 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. The MCR bits are defined in the following bulleted list.

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 can be input into an inverting line driver in order to obtain the

proper polarity input at the modem or data set.

D

Bit 1: When MCR1 is set, the RTS output is forced low. When MCR1 is cleared, the R TS output is forced
high. The RTS

output of the serial channel can be input into an inverting line driver to obtain the proper

polarity input at the modem or data set.

D

Bit 2: MCR2 has no effect on operation.

D

Bit 3: When MCR3 is set, the external serial channel interrupt is enabled.

D

Bit 4: MCR4 provides a local loopback feature for diagnostic testing of the channel. When MCR4 is set,
SOUT is set to the marking (high) state and the SIN is disconnected. The output of the transmitter shift
register is looped back into the receiver shift register input. The four modem control inputs (CTS

, DSR, DCD,

and RI

) are disconnected. The modem control outputs (DTR, RTS, OUT1, and OUT2) are internally
connected to the four modem control inputs. The modem control output terminals are forced to their inactive
(high) state on the TL16C552A. 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.

TL16C552A, TL16C552AM
DUAL ASYNCHRONOUS COMMUNICATIONS ELEMENT
WITH FIFO

SLLS189D – NOVEMBER 1994 – REVISED JANUARY 1999

30

POST OFFICE BOX 655303 • DALLAS, TEXAS 75265

PRINCIPLES OF OPERATION

modem control register (MCR) (continued)

D

Bits 5 – 7: MCR5 – MCR7 are permanently cleared.

MCR7MCR6MCR5MCR4MCR3MCR2MCR1MCR

0

Modem Control Register

Data Terminal
Ready

Request
to Send

Out 1
(internal)

Out 2
(internal)

Loop

0 = Loop Disabled
1 = Loop Enabled

0 = DTR Output High (inactive)
1 = DTR

Output Low (active)

0 = RTS

Output High (inactive)

1 = RTS

Output Low (active)

No Effect on External Operation

0 = External Interrupt Disabled
1 = External Interrupt Enabled

Bits Are Cleared

Figure 20. Modem Control Register Contents

modem status register (MSR)

The MSR provides the CPU with status of the modem input lines from the modem or peripheral devices. The
MSR allows the CPU to read the serial channel modem signal inputs. This is done by accessing the data bus
interface of the ACE in addition to the current status of four bits of the MSR. These four bits 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 state and are cleared when the CPU reads the MSR.

The modem input lines are CTS

, DSR, RI, and DCD. MSR4 – MSR7 are status indicators of these lines. A set
status bit indicates that the input is low. A cleared status bit indicates that the input is high. When the modem
status interrupt in the interrupt enable register is enabled (IER3), 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 11.

D

Bit 0: MSR0 is the delta clear-to-send (∆CTS) bit. ∆CTS displays that the CTS input to the serial channel
has changed states since it was last read by the CPU.

D

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.

D

Bit 2: MSR2 is the trailing edge of the ring indicator (TERI) bit. TERI indicates that the RI 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.

TL16C552A, TL16C552AM

DUAL ASYNCHRONOUS COMMUNICATIONS ELEMENT

WITH FIFO

SLLS189D – NOVEMBER 1994 – REVISED JANUARY 1999

31

POST OFFICE BOX 655303 • DALLAS, TEXAS 75265

PRINCIPLES OF OPERATION

modem status register (MSR) (continued)

D

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.

D

Bit 4: MSR4 is the clear-to-send (CTS) bit. CTS is the complement of the CTS input from the modem that
indicates to the serial channel that the modem is ready to receive data from SOUT . When the serial channel
is in the loop mode (MCR4 is set), MSR4 reflects the value of RTS in the MCR.

D

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 to the serial channel
receiver circuitry . When the channel is in loop mode (MCR4 is set), MSR5 reflects the value of DTR in the
MCR.

D

Bit 6: MSR6 is the ring indicator (RI) bit. RI is the complement of the RI input. When the channel is in loop
mode (MCR4 is set), MSR6 reflects the value of OUT1

in the MCR.

D

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 loop mode (MCR4 is set), MSR7 reflects the value of OUT2 in

the MCR.
Reading the MSR register clears the delta modem status indicators but has no effect 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 loop back mode, when modem status
interrupts are enabled, the CTS

, DSR, RI and DCD input terminals are ignored; however, a modem status
interrupt can still be generated by writing to MCR3–MCR0. Applications software should not write to the
MSR.

Table 11. Modem Status Register Bits

MSR BIT MNEMONIC DESCRIPTION

MSR0 ∆CTS Delta clear to send
MSR1 ∆DSR Delta data set ready
MSR2 TERI Trailing edge of ring indicator
MSR3 ∆DCD Delta data carrier detect
MSR4 CTS Clear to send
MSR5 DSR Data set ready
MSR6 RI Ring indicator
MSR7 DCD Data carrier detect

TL16C552A, TL16C552AM
DUAL ASYNCHRONOUS COMMUNICATIONS ELEMENT
WITH FIFO

SLLS189D – NOVEMBER 1994 – REVISED JANUARY 1999

32

POST OFFICE BOX 655303 • DALLAS, TEXAS 75265

PRINCIPLES OF OPERATION

parallel port registers

The TL16C552A parallel port can connect the device to a Centronic-style printer interface. When chip select 2
(CS2

) is low, the parallel port is selected. Table 12 shows the registers associated with this parallel port. The

read or write function of the register is controlled by the state of the read (IOR

) and write (IOW) terminals as

shown. The read data register allows the microprocessor to read the information on the parallel bus.
The read status register allows the microprocessor to read the status of the printer in the six most significant

bits. The status bits are printer busy BSY

, acknowledge (ACK) (a handshake function), paper empty (PE), printer

selected (SLCT

), error (ERR), and printer interrupt (PRINT). The read control register allows the state of the
control lines to be read. The write control register sets the state of the control lines. They are direction (DIR),
interrupt enable (INT2 EN), select in (SLIN), initialize the printer (INIT), autofeed the paper (AFD), and strobe
(STB

), which informs the printer of the presence of a valid byte on the parallel bus. The write data register allows
the microprocessor to write a byte to the parallel bus. The parallel port is completely compatible with the parallel
port implementation used in the IBM serial parallel adapter.

T able 12. Parallel Port Registers

REGISTER BITS

REGISTER

BIT 7 BIT 6 BIT 5 BIT 4 BIT 3 BIT 2 BIT 1 BIT 0

Read data PD7 PD6 PD5 PD4 PD3 PD2 PD1 PD0
Read status BSY ACK PE SLCT ERR PRINT 1 1
Read control 0 0 PEMD • DIR INT2 EN SLIN INIT AFD STB
Write data PD7 PD6 PD5 PD4 PD3 PD2 PD1 PD0
Write control 0 0 DIR INT2 EN SLIN INIT AFD STB

T able 13. Parallel Port Register Select

CONTROL PINS

IOR IOW CS2 A1 A0

REGISTER SELECTED

L H L L L Read data
L H L L H Read status
L H L H L Read control
L H L H H Invalid
H L L L L Write data
H L L L H Invalid
H L L H L Write control
H L L H H Invalid

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). The output frequency of the baud generator is 16x the data rate [divisor
# = clock ÷ (baud rate x 16)], referred to in this document as RCLK. 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 to
512 kbps are available. Tables 14, 15, 16, and 17 illustrate the divisors needed to obtain standard rates using
these three frequencies.

TL16C552A, TL16C552AM

DUAL ASYNCHRONOUS COMMUNICATIONS ELEMENT

WITH FIFO

SLLS189D – NOVEMBER 1994 – REVISED JANUARY 1999

33

POST OFFICE BOX 655303 • DALLAS, TEXAS 75265

PRINCIPLES OF OPERATION

programmable baud rate generator (continued)

Table 14. Baud Rates Using a 1.8432-MHz Crystal

BAUD RATE

DESIRED

DIVISOR (N) USED TO

GENERATE 16x CLOCK

PERCENT ERROR DIFFERENCE

BETWEEN DESIRED AND ACTUAL

50
75

110

134.5
150
300
600

1200
1800
2000
2400
3600
4800
7200

9600
19200
38400
56000

2304
1536
1047

857
768
384
192

96
64
58
48
32
24
16
12

6
3
2

–
–

0.026

0.058
–
–
–
–
–

0.690
–
–
–
–
–
–
–

2.860

Table 15. Baud Rates Using a 3.072-MHz Crystal

BAUD RATE

DESIRED

DIVISOR (N) USED TO

GENERATE 16x CLOCK

PERCENT ERROR DIFFERENCE

BETWEEN DESIRED AND ACTUAL

50
75

110

134.5
150
300
600

1200
1800
2000
2400
3600
4800
7200

9600
19200
38400

3840
2560
1745
1428
1280

640
320
160
107

96
80
53
40
27
20
10

5

–
–

0.026

0.034
–
–
–
–

0.312
–
–

0.628
–

1.230
–
–
–

TL16C552A, TL16C552AM
DUAL ASYNCHRONOUS COMMUNICATIONS ELEMENT
WITH FIFO

SLLS189D – NOVEMBER 1994 – REVISED JANUARY 1999

34

POST OFFICE BOX 655303 • DALLAS, TEXAS 75265

PRINCIPLES OF OPERATION

programmable baud rate generator (continued)

Table 16. Baud Rates Using an 8-MHz Clock

BAUD RATE

DESIRED

DIVISOR (N) USED TO

GENERATE 16x CLOCK

PERCENT ERROR DIFFERENCE

BETWEEN DESIRED AND ACTUAL

50
75

110

134.5
150
300
600

1200
1800
2000
2400
3600
4800
7200

9600
19200
38400
56000

128000
256000
512000

10000

6667
4545
3717
3333
1667

833
417
277
250
208
139
104

69
52
26
13

9
4
2
1

–

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

Table 17. Baud Rates Using a 16-MHz Clock

BAUD RATE

DESIRED

DIVISOR (N) USED TO

GENERATE 16x CLOCK

PERCENT ERROR DIFFERENCE

BETWEEN DESIRED AND ACTUAL

50
75

110

134.5
150
300
600

1200
1800
2000
2400
3600
4800
7200

9600
19200
38400
56000

128000
256000
512000

1000000

20000
13334

9090
7434
6666
3334
1666

834
554
500
416
278
208
138
104

52
26
18

8
4
2
1

0.00

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

TL16C552A, TL16C552AM

DUAL ASYNCHRONOUS COMMUNICATIONS ELEMENT

WITH FIFO

SLLS189D – NOVEMBER 1994 – REVISED JANUARY 1999

35

POST OFFICE BOX 655303 • DALLAS, TEXAS 75265

PRINCIPLES OF OPERATION

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 to in any order, the IER should be written to 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.

receiver

Serial asynchronous data is input into SIN. 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 if SIN 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 SIN input.

The LCR determines the number of data bits in a character (LCR0 and LCR1). When parity is used, LCR3 and
the polarity of parity LCR4 is 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 receiver
buffer register, 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.

If the data into SIN 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.

scratchpad register

The scratch register is an 8-bit read/write register that has no effect on either channel in the ACE. It is intended
to be used by the programmer to hold data temporarily.

TL16C552A, TL16C552AM
DUAL ASYNCHRONOUS COMMUNICATIONS ELEMENT
WITH FIFO

SLLS189D – NOVEMBER 1994 – REVISED JANUARY 1999

36

POST OFFICE BOX 655303 • DALLAS, TEXAS 75265

MECHANICAL DATA

HV (S-GQFP-F68) CERAMIC QUAD FLATPACK

0.400 (10,16) TYP

4040072/C 04/96

0.485 (12,32)

0.500 (12,70)

0.008 (0,203)

0.013 (0,330)

SQ

SQ

1.500 (38,10)

1.300 (33,02)

0.154 (3,912)

0.134 (3,404)

0.005 (0,127)

0.007 (0,178)

9

61

60 44

43

27

2610

1

0.025 (0,635)

NOTES: A. All linear dimensions are in inches (millimeters).

B. This drawing is subject to change without notice.

C. This package can be hermetically sealed with a ceramic lid using glass frit.

TL16C552A, TL16C552AM

DUAL ASYNCHRONOUS COMMUNICATIONS ELEMENT

WITH FIFO

SLLS189D – NOVEMBER 1994 – REVISED JANUARY 1999

37

POST OFFICE BOX 655303 • DALLAS, TEXAS 75265

MECHANICAL DATA

FK (S-CQCC-N**) LEADLESS CERAMIC CHIP CARRIER

4040140/D 10/96

28 TERMINAL SHOWN

B

0.358
(9,09)

MAX

(11,63)

0.560

(14,22)

0.560

0.458

0.858
(21,8)

1.063
(27,0)

(14,22)

A

NO. OF

MINMAX

0.358

0.660

0.761

0.458

0.342
(8,69)

MIN

(11,23)

(16,26)

0.640

0.739

0.442

(9,09)

(11,63)

(16,76)

0.962

1.165

(23,83)

0.938

(28,99)

1.141

(24,43)

(29,59)

(19,32)(18,78)

**

20

28

52

44

68

84

0.020 (0,51)

TERMINALS

0.080 (2,03)

0.064 (1,63)

(7,80)

0.307

(10,31)

0.406

(12,58)

0.495

(12,58)

0.495

(21,6)

0.850

(26,6)

1.047

0.045 (1,14)

0.045 (1,14)

0.035 (0,89)

0.035 (0,89)

0.010 (0,25)

121314151618 17

11

10

8

9

7

5

432

0.020 (0,51)

0.010 (0,25)

6

12826 27

19

21

B SQ

A SQ

22

23

24

25

20

0.055 (1,40)

0.045 (1,14)

0.028 (0,71)

0.022 (0,54)

0.050 (1,27)

NOTES: A. All linear dimensions are in inches (millimeters).

B. This drawing is subject to change without notice.
C. This package can be hermetically sealed with a metal lid.
D. The terminals are gold plated.
E. Falls within JEDEC MS-004

TL16C552A, TL16C552AM
DUAL ASYNCHRONOUS COMMUNICATIONS ELEMENT
WITH FIFO

SLLS189D – NOVEMBER 1994 – REVISED JANUARY 1999

38

POST OFFICE BOX 655303 • DALLAS, TEXAS 75265

MECHANICAL DATA

PN (S-PQFP-G80) PLASTIC QUAD FLATPACK

4040135 /B 1 1/96

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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