COM20020 datasheet(5/72 Pages) SMSC

5 / 72 page

DESCRIPTION OF PIN FUNCTIONS

DIP PIN

NO.

PLCC PIN

NO.

NAME

SYMBOL

DESCRIPTION

MICROCONTROLLER INTERFACE

1-3

Address

0-2

A0/nMUX,

A1,A2/ALE

Input.

On a non-multiplexed mode, A0-A2

are address input bits. (A0 is the LSB) On a

multiplexed address/data bus, nMUX tied

Low, A1 is left open, and ALE is tied to the

Address

Latch

Enable

signal.

connected to an internal pull-up resistor.

4-11

4-6,8-12

Data 0-7

AD0-AD2,

D3-D7

Input/Output.

On a non-multiplexed bus,

these signals are used as the data lines for

the device.

On a multiplexed address/data

bus, AD0-AD2 act as the address lines

(latched by ALE) and as the low data lines for

the device. D3-D7 are always used for data

only. These signals are connected to internal

pull-up resistors.

nRead/nData

Strobe

nRD/nDS

Input. On a 68XX-like bus, nDS is an active

low signal issued by the microcontroller as the

data strobe signal to strobe the data onto the

bus. On a 80XX-like bus, nRD is an active

low signal issued by the microcontroller to

indicate a read operation.

nWrite/

Direction

nWR/DIR

Input. On a 68XX-like bus, DIR is issued by

the microcontroller as the Read/nWrite signal

to determine the direction of data transfer. In

this case, a logic "1" selects a read operation,

while a logic "0" selects a write operation. In

this case, data is actually strobed by the nDS

signal.

On an 80XX-like bus, nWR is an

active low signal issued by the microcontroller

to indicate a write operation. In this case, a

logic "0" on this pin, when the COM20020 is

accessed, enables data from the data bus to

be written to the device.

nReset in

nRESET

Input.

This active low signal executes a

hardware reset.

nInterrupt

nINTR

Output. This active low signal is generated by

the COM20020 when an enabled interrupt

condition occurs.

nChip Select

nCS

Input.

This active low signal selects the

COM20020 for an access.

TRANSMISSION MEDIA INTERFACE

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