AT89C51

4-34

Program Verify: If lock bits LB1 and LB2 have not been

programmed, the programmed code data can be read back

via the address and data lines for verification. The lock bits

cannot be verified directly. Verification of the lock bits is

achieved by observing that their features are enabled.

Chip Erase:

The entire Flash array is erased electrically

by using the proper combination of control signals and by

holding ALE/PROG low for 10 ms. The code array is written

with all “1”s. The chip erase operation must be executed

before the code memory can be re-programmed.

Reading the Signature Bytes: The signature bytes are

read by the same procedure as a normal verification of

locations 030H,

031H, and 032H, except that P3.6 and P3.7 must be pulled

to a logic low. The values returned are as follows.

(030H) = 1EH indicates manufactured by Atmel

(031H) = 51H indicates 89C51

(032H) = FFH indicates 12V programming

(032H) = 05H indicates 5V programming

Programming Interface

Every code byte in the Flash array can be written and the

entire array can be erased by using the appropriate combi-

nation of control signals. The write operation cycle is self-

timed and once initiated, will automatically time itself to

completion.

All major programming vendors offer worldwide support for

the Atmel microcontroller series. Please contact your local

programming vendor for the appropriate software revision.

Flash Programming Modes

Note:

1. Chip Erase requires a 10-ms PROG pulse.

Mode

RST

PSEN

ALE/PROG

P2.6

P2.7

P3.6

P3.7

Write Code Data

H

L

H/12V

L

H

H

H

Read Code Data

H

L

H

H

L

L

H

H

Write Lock

Bit - 1

H

L

H/12V

H

H

H

H

Bit - 2

H

L

H/12V

H

H

L

L

Bit - 3

H

L

H/12V

H

L

H

L

Chip Erase

H

L

H/12V

H

L

L

L

Read Signature Byte

H

L

H

H

L

L

L

L

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