TL16C451, TL16C452

ASYNCHRONOUS COMMUNICATIONS ELEMENTS

SLLS053C – MAY 1989 – REVISED AUGUST 1999

6

POST OFFICE BOX 655303

Terminal Functions (continued)

TERMINAL

I/O

DESCRIPTION

NAME†

NO.

I/O

DESCRIPTION

PD0 – PD7

53 – 46

I/O

Parallel data bits (0 – 7). These eight lines provide a byte-wide input or output port to the system. The

eight lines are held in a high-impedance state when LPTOE is high.

PE

67

I

Printer paper empty. This is an input line from the printer that goes high when the printer runs out of

paper.

RESET

39

I

Reset. When active (low), RESET clears most ACE registers and sets the state of various output

signals. Refer to Table 2.

RI0

RI1 [GND]

30

6

I

Ring indicator. RIx is an active-low modem status signal. Its state can be checked by reading bit 6 (RI)

of the modem status register. Bit 2 (TERI) of the modem status register indicates that the RIx input has

transitioned from a low to a high state since the last read from the modem status register. If the modem

status interrupt is enabled when this transition occurs, an interrupt is generated.

RLSD0

RLSD1 [GND]

29

8

I

Receive line signal detect. RLSDx is an active-low modem status signal. Its state can be checked by

reading bit 7 of the modem status register. Bit 3 (DRLSD) of the modem status register indicates that

this signal has changed states since the last read from the modem status register. If the modem status

interrupt is enabled when RLSDx changes state, an interrupt is generated. This bit is low when a data

carrier is detected.

RTS0

RTS1 [NC]

24

12

O

Request to send. When active (low), RTSx informs the modem or data set that the ACE is ready to

transmit data. RTSx is set to its active state by setting the RTS modem control register bit and is set

to its inactive (high) state either as a result of a reset or during loop mode operations or by clearing bit

1 (RTS) of the modem control register.

SIN0

SIN1 [GND]

41

62

I

Serial input. SINx is a serial data input from a connected communications device.

SLCT

65

I

Printer selected. SLCT is an input line from the printer that goes high when the printer has been selected.

SLIN

58

I/O

Printer select. SLIN is an open-drain line that selects the printer when it is active (low). An internal pullup

is provided on this line.

SOUT0

SOUT1 [NC]

26

10

I

Serial output. SOUTx is a composite serial data output to a connected communication device. SOUTx

is set during a reset.

STB

55

I/O

Printer strobe. STB is an open-drain line that provides communication synchronization between the

TL16C451/TL16C452 and the printer. When it is active (low), it provides the printer with a signal to latch

the data currently on the parallel port. An internal pullup is provided on this line.

VCC

23,40,

64

5-V supply voltage

GND

2,7,9

22,27,42,

43,54,61

Supply common

† Names shown in brackets are for the TL16C451.