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EN87C51FA1SF76

CHMOS SINGLE-CHIP 8-BIT MICROCONTROLLER

Atmel Corporation 

87C51/80C51BH/80C31BH

Program Lock Bits

The 87C51 has 3 programmable lock bits that when

programmed according to Table 5 will provide differ-

ent levels of protection for the on-chip code and

data.

Erasing the EPROM also erases the encryption ar-

ray and the program lock bits, returning the part to

full functionality.

Reading the Signature Bytes

The 87C51 and 80C51BH have 3 signature bytes in

locations 30H, 31H, and 60H. To read these bytes

follow the procedure for EPROM verify, but activate

the control lines provided in Table 4 for Read Signa-

ture Byte.

Location

30H

31H

60H

Device

All

All

87C51

80C51BH

Contents

89H

58H

51H

11H

Erasure Characteristics

(Windowed Devices Only)

Erasure of the EPROM begins to occur when the

chip is exposed to light with wavelengths shorter

than approximately 4,000 Angstroms. Since sunlight

and fluorescent lighting have wavelengths in this

range, exposure to these light sources over an ex-

tended time (about 1 week in sunlight, or 3 years in

room level fluorescent lighting) could cause inadver-

tent erasure. If an application subjects the device to

this type of exposure, it is suggested that an opaque

label be placed over the window.

The recommended erasure procedure is exposure

to ultraviolet light (at 2537 Angstroms) to an integrat-

ed dose of at least 15 W-sec/cm 2. Exposing the

EPROM to an ultraviolet lamp of 12,000 mW/cm 2

rating for 30 minutes, at a distance of about 1 inch,

should be sufficient.

Erasure leaves the array in an all 1's state.

Program Lock Bits

LB1 LB2 LB3

1U

U

U

2P

U

U

3P

P

U

4P

P

P

Table 5. Program Lock Bits and the Features

Protection Type

No program lock features enabled. (Code verify will still be encrypted by the

encryption array if programmed.)

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 EPROM is disabled.

Same as 2, also verify is disabled.

Same as 3, also external execution is disabled.

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