COM90C66 datasheet(4/76 Pages) SMSC

4 / 76 page

DESCRIPTION OF PIN FUNCTIONS

PLCC

PIN NO.

NAME

SYMBOL

DESCRIPTION

PROCESSOR INTERFACE

75-84, 2-

Address 0-19

A0-A19

Input. These signals are connected to the address lines

of the host processor and are used to access memory

and I/O locations of the COM90C66, as well as to access

the external ROM through the COM90C66.

13-20,

22-29

Data 0-15

D0-D15

Input/Output.

These signals are used by the host to

transmit data to and from the internal registers and buffer

memory of the COM90C66 and are connected to weak

internal pull-up resistors.

63, 62

nTransceiver

Direction

Control

nTOPL,

nTOPH

Output.

These active low signals control the data bus

transceiver. When these signals are high, data gets sent

from the PC to the COM90C66. When these signals are

low, data gets sent from the COM90C66 to the PC, or

from the PROM to the PC if the PROM signal is also low.

I/O Channel

Ready

IOCHRDY

Output. This signal, when low, is optionally used by the

COM90C66 to extend host cycles. This is an open-drain

signal. An external pull-up resistor is typically provided

by the system.

Address

Enable

AEN

Input. This signal, when low, acts as a qualifier for I/O

Address Selection.

When the signal is high, I/O

decoding is disabled. This signal has no effect on

Memory Address Selection.

Address Latch

Enable

BALE

Input.

The falling edge of this signal is used by the

COM90C66 to latch the A0-A19 lines and the nSBHE

signal via an internal transparent latch.

This signal is

connected to a weak internal pull-up resistor.

nI/O Read

nIOR

Input.

This active low signal is issued by the host

microprocessor to indicate an I/O Read operation. A low

level on this pin when the COM90C66 is accessed

enables

data

from

the

internal

registers

the

COM90C66.

nI/O Write

nIOW

Input.

This active low signal is issued by the host

microprocessor to indicate an I/O Write operation. A low

pulse on this pin when the COM90C66 is accessed

enables data from the Data Bus into the internal registers

of the COM90C66.

COM90C66 датащи(PDF) 4 Page - SMSC Corporation

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