AT80F51

3-7

nated. The only exit from power down is a hardware reset.

Reset redefines the SFRs but does not change the on-chip

restored to its normal operating level and must be held

active long enough to allow the oscillator to restart and sta-

bilize.

Program Memory Lock Bits

On the chip are three lock bits which can be left unpro-

grammed (U) or can be programmed (P) to obtain the addi-

tional features listed in the table below:

When lock bit 1 is programmed, the logic level at the EA pin

is sampled and latched during reset. If the device is pow-

ered up without a reset, the latch initializes to a random

value, and holds that value until reset is activated. It is nec-

essary that the latched value of EA be in agreement with

the current logic level at that pin in order for the device to

function properly.

Lock Bit Protection Modes

Program Lock Bits

Protection Type

LB1

LB2

LB3

1

U

U

U

No program lock features.

2

P

U

U

MOVC instructions executed from external program memory are disabled from fetching code

bytes from internal memory, EA is sampled and latched on reset, and further programming of the

QuickFlash is disabled.

3

P

P

U

Same as mode 2, also verify is disabled.

4

P

P

P

Same as mode 3, also external execution is disabled.

Programming/Verifying the QuickFlash

The AT80F51 can only be programmed by Atmel. Cus-

tomer codes should be submitted in duplicate on a floppy

disk or uploaded to Atmel’s bulletin board or Web site. The

code should be in the Intel Hex format. The desired states

of the Lock Bits should be specified. Once programmed,

the code memory and Lock Bits cannot be erased or repro-

grammed.

Please consult the factory or Atmel’s representatives for

details on submitting custom codes.

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.

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) = 80H indicates QuickFlash

(032H) = 01H indicates AT80F51

QuickFlash Verification Modes

Mode

RST

PSEN

ALE

EA

P2.6

P2.7

P3.6

P3.7

Read Code Data

H

L

H

H

L

L

H

H

Read Signature Byte

H

L

H

H

L

L

L

L