COM81C17 datasheet(5/18 Pages) SMSC

5 / 18 page

DESCRIPTION OF PIN FUNCTIONS

DIP PIN NO.

NAME

SYMBOL

DESCRIPTION

1, 2, 5-7,

9,11-12

DATA BUS

D0-D7

An 8-bit bi-driectional DATA BUS is used to

interface the TPUART to the processor Data Bus.

CHIP SELECT

nCS

A low level on this input enables the TPUART for

reading and writing to the processor. When nCS is

high, the DATA BUS is in high impedance and the

nWR and nRD will have no effect on the chip.

READ DATA

STROBE

nRD

A low pulse on this input (when nCS is low) enables

the TPUART to place the data or the status

information on the DATA BUS.

WRITE DATA

STROBE

nWR

A low pulse on this input (when nCS is low) enables

the TPUART to accept the data or control word

from the DATA BUS into the TPUART.

GROUND

GND

Power Supply Return.

CLOCK

CLK

External TTL Clock Input (See Table 2)

INTERRUPT

REQUEST

nINT

An interrupt request is asserted by the TPUART

when an enabled condition has occurred in the

Status Register. This is an active low, open drain

output. This pin has an internal pullup register.

SELECT

During processor to TPUART communications, this

input is used to indicate which internal register will

be selected for access by the processor. When this

input is low, data can be written to the TX Holding

Buffer or data can be read from the RX Holding

be written to the Control Register or status

information can be read from the Status Register.

RECEIVER DATA

This input is the receiver serial data. A high to low

transition is required to initiate data reception.

TRANSMITTER

DATA

This output is the transmitted serial data from the

TPUART. When a transmission is concluded, the

TX line will always return to the mark (High) state.

CONTROL PIN 1

nCP1

This control pin is an input only pin.

It can be

programmed to perform the functions of CTS or

DSR/DCD.

CONTROL PIN 2

nCP2

This control pin can be programmed to be either an

input or an output. When in input mode, this pin

can perform the functions of DSR/DCD. When in

output mode, this pin can perform the functions of

DTR or RTS.

POWER SUPPLY

VCC

+5V Supply Voltage

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