Intel 8XC251SP User Manual

14-5

           

The procedure for programming the 87C251Sx is as follows:

1.

Set up the controller for operation in the appropriate mode according to Table 14-1. 

2.

Input the 16-bit address on ports 1 and 3.

3.

Input the data byte on port 2.

4.

Raise the voltage on the V

PP

 pin from 5 V to 12.75 V.

5.

Pulse the PROG# pin 5 times for the on-chip code memory and the configuration bytes,
and 25 times for the encryption array and the lock bits. 

6.

Reduce the voltage on the V

PP

 pin to 5 V.

7.

If the procedure is program/immediate-verify, go to section 14.5, “Verify Algorithm,” and
perform steps 1 through 4 to verify the currently addressed byte. Make sure the voltage on
the EA#/V

PP

 pin has been lowered to 5 V before performing the verifying procedure. 

8.

Repeat steps 1 through 7 until all memory locations are programmed. 

P0

PSEN#

ALE/PROG#

EA#/V

pp

x

A4122-02

4 MHz

to

6 MHz

XTAL2

A0 - A7

A8 - A15

P3

P1

Data
(8 Bits)

V

SS

V

CC

V

CC

XTAL1

Programming
Signals

Address
(16 Bits)

Program/Verify Mode
(8 Bits)

P2

RST