COM20020ILJP datasheet(9/72 Pages) MICROCHIP

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5Mbps ARCNET (ANSI 878.1) Controller with 2K x 8 On-Chip RAM

Datasheet

SMSC COM20020I Rev D

Page 9

Revision 12-05-06

DATASHEET

Chapter 3

Description of Pin Functions

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. A1 is connected to an internal

pull-up resistor.

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 COM20020ID 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

COM20020ID when an enabled interrupt condition occurs.

nChip Select

nCS

Input. This active low signal selects the COM20020ID for

an access.

TRANSMISSION MEDIA INTERFACE

19,18

nPulse 2,

nPulse 1

nPULSE2,

nPULSE1

Output (nPULSE1), Input/Output (nPULSE2). In Normal

Mode, these active low signals carry the transmit data

information, encoded in pulse format, as DIPULSE

waveform. When the device is in Backplane Mode, the

nPULSE1 signal driver is programmable (push/pull or open-

drain), while the nPULSE2 signal provides a clock with

frequency of double the data rate. nPULSE1 is connected

to a weak internal pull-up resistor on the open/drain driver

in backplane mode.

Receive In

RXIN

Input. This signal carries the receive data information from

the line transceiver.

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