X88064

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PRINCIPLES OF OPERATION

The X88064 is a highly integrated peripheral device for a

wide variety of single-chip microcontrollers. The X88064

for Program Storage, Data Storage, or a combination of

both, in systems based upon Harvard (80XX) architec-

tures. The X88064 incorporates the interface circuitry

normally needed to decode the control signals and

demultiplex the Address/Data bus to provide a “Seam-

less” interface.

The interface inputs on the X88064 are configured such

that it is possible to directly connect them to the proper

interface signals of the appropriate single-chip microcon-

troller. In the Harvard type system, the reading of data

from the chip is controlled either by the PSEN or the RD

signal, which essentially maps the X88064 into both the

Program and the Data Memory address map.

The X88064 also features an advanced implementation

of the Software Data Protection scheme, called Block

Lock, which allows the device to be broken into 8 inde-

pendent sections of 1K bytes. Each of these sections can

be independently enabled for write operations; thereby

allowing certain sections of the device to be secured so

that updates can only occur in a controlled environment

(e.g. in an automotive application, only at an authorized

service center). The desired set-up configuration is

stored in a nonvolatile register, ensuring the configuration

data will be maintained after the device is powered down.

The X88064 also features a Write Control input (WC),

which serves as an external control over the completion

of a previously initiated page load cycle.

The X88064 also features the industry standard

write and Toggle Bit Polling.

DEVICE OPERATION MODES

Mixed Program/Data Memory

By properly assigning the address space, a single

X88064 can be used as both the Program and Data

Memory. This would be accomplished by connecting all

of the Microcontroller control outputs to the correspond-

ing inputs of the X88064.

The Data Storage can be fully protected by enabling

Block Lock Control.

Program Memory Mode

This mode of operation is read-only. The PSEN and ALE

inputs of the X88064 are tied directly to the PSEN and

ALE outputs of the microcontroller. The RD and WR

inputs are tied HIGH.

addresses flow into the device. The addresses, both low

and high order, are latched when ALE transitions LOW

during the entire operation.

Data Memory Mode

This mode of operation allows both read and write func-

pull-up resistor. The ALE, RD, and WR inputs are tied

directly to the microcontroller’s ALE, RD, and WR out-

puts.

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 A/D pins

Write

A write is performed by latching the addresses on the fall-

ing edge of ALE. Then WR is strobed LOW followed by

data will be latched into the X88064 on the rising edge of

WR. To write to the X88064, with the SDP feature

enabled, a three-byte command sequence must precede

the byte(s) being written. (See Software Data Protec-

tion.)