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
Mode
Write Code Data
RST
H
PSEN
L
ALE/PROG
EA/V
PP
H/12V
P2.6
L
P2.7
H
P3.6
H
P3.7
H
Read Code Data
Write Lock
Bit - 1
H
H
L
L
H
H
H/12V
L
H
L
H
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
(1)
H/12V
H
L
L
L
Read Signature Byte
H
L
Note:
1. Chip Erase requires a 10-ms PROG pulse.
H
H
L
L
L
L
4-34
AT89C51
ATMEL [ ATMEL CORPORATION ]
