COM90C66 datasheet(5/76 Pages) SMSC

5 / 76 page

DESCRIPTION OF PIN FUNCTIONS

PLCC

PIN NO.

NAME

SYMBOL

DESCRIPTION

nMemory Read nMEMR

Input.

This active low signal is issued by the host

microprocessor to indicate a Memory Read operation. A

low level on this pin when the COM90C66 is accessed

enables data from the internal RAM of the COM90C66 or

the PROM onto the data bus to be read by the host.

nMemory

Write

nMEMW

Input.

This active low signal is issued by the host

microprocessor to indicate a Memory Write operation. A

low pulse on this pin when the COM90C66 is accessed

enables data from the data bus into the internal RAM of

the COM90C66.

Reset In

RESETIN

Input. This active high signal is the power on reset signal

from the host.

It is used to activate the internal reset

circuitry within the COM90C66.

nROM Enable

nENROM

Input. This active low signal enables the decoding of the

external PROM.

This signal also affects the timing of

IOCHRDY and the number of address lines used to

decode nMEMCS16. This signal is connected to a weak

internal pull-up resistor.

nROM Select

nPROM

Output.

This active low signal is issued by the

COM90C66 to enable the external 8-bit wide PROM or

the external register of the COM90C66.

Interrupt

Request

INTR

Output.

This active high signal is generated by the

COM90C66 when an enabled interrupt condition occurs.

INTR returns to its inactive state when the interrupt

status condition or the corresponding interrupt mask bit

is reset.

nZero Wait

State

n0WS

Output. This active low signal is used to force zero wait

state access cycles on the IBM PC Bus. This is an open-

drain signal.

An external pull-up resistor is typically

provided by the system.

nMemory

16-Bit Chip

Select

nMEMCS16

Output. This active low signal is used to indicate that the

present data transfer is a 16-bit memory cycle.

The

COM90C66 can be configured to use A19-A17 or A19-

A11 to generate nMEMCS16.

This is an open-drain

signal. An external pull-up resistor is typically provided

by the system.

COM90C66 Datasheet(PDF) 5 Page - SMSC Corporation

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