X88C64

4

Data Memory Mode

This mode of operation allows both read and write

functions. The

through a pull-up resistor. The ALE,

RD, and WR inputs

are tied directly to the microcontroller’s ALE,

RD, and

WR outputs.

Read

This operation is quite similar to the Program Memory

read. A HIGH to LOW transition on ALE latches the

addresses and the data will be output on the AD pins

after

Write

A write is performed by latching the addresses on the

falling edge of ALE. Then

WR is strobed LOW followed

The data will be latched into the X88C64 on the rising

edge of

WR. To write to the X88C64, a three-byte

command sequence must precede the byte(s) being

written. (See Software Data Protection.)

MODE SELECTION

CE

PSEN

RD

WR

Mode

I/O

Power

X

X

X

Standby

High Z

Standby (CMOS)

HIGH

X

X

X

Standby

High Z

Standby (TTL)

LOW

LOW

HIGH

HIGH

Program Fetch

Active

LOW

HIGH

LOW

HIGH

Data Read

Active

LOW

HIGH

HIGH

Write

Active

3867 PGM T02.2