80C52 datasheet(21/23 Pages) INTEL

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8XC525458

ROM and EPROM Lock System

The program lock system when programmed pro-

tects the onboard program against software piracy

The 80C5X has a one-level program lock system

and a 64-byte encryption table See line 2 of Table

5 If program protection is desired the user submits

the encryption table with their code and both the

lock-bit and encryption array are programmed by the

factory The encryption array is not available without

the lock bit For the lock bit to be programmed the

user must submit an encryption table

The 87C5X has a 3-level program lock system and a

64-byte encryption array Since this is an EPROM

device all locations are user-programmable See

Table 5

Encryption Array

Within the EPROM array are 64 bytes of Encryption

Array that are initially unprogrammed (all 1’s) Every

time that a byte is addressed during a verify 6 ad-

dress lines are used to select a byte of the Encryp-

tion Array

This byte is then exclusive-NOR’ed

(XNOR) with the code byte creating an Encryption

Verify byte The algorithm with the array in the un-

programmed state (all 1’s) will return the code in its

original unmodified form For programming the En-

cryption Array refer to Table 4 (Programming the

EPROM)

When using the encryption array one important fac-

tor needs to be considered If a code byte has the

value 0FFH verifying the byte will produce the en-

cryption byte value If a large block (l64 bytes) of

code is left unprogrammed a verification routine will

display the contents of the encryption array For this

reason all unused code bytes should be pro-

grammed with some value other than 0FFH and not

all of them the same value This will ensure maxi-

mum program protection

Program Lock Bits

The 87C5X 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 8XC5X has 3 signature bytes in locations 30H

31H and 60H To read these bytes follow the proce-

dure for EPROM verify but activate the control lines

provided in Table 4 for Read Signature Byte

Location

Device

Contents

30H

All

89H

31H

All

58H

60H

80C52

12H

87C52

52H

80C54

14H

87C54

54H

80C58

18H

87C58

58H

Erasure Characteristics

(Windowed Packages Only)

Erasure of the EPROM begins to occur when the

chip is exposed to light with wavelength shorter than

approximately 4000 Angstroms Since sunlight and

fluorescent lighting have wavelengths in this range

exposure to these light sources over an extended

time (about 1 week in sunlight or 3 years in room-

level fluorescent lighting) could cause inadvertent

erasure If an application subjects the device to this

type of exposure it is suggested that an opaque la-

bel 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-seccm2 Exposing the

EPROM to an ultraviolet lamp of 12000 mWcm2

rating for 30 minutes at a distance of about 1 inch

should be sufficient

Erasure leaves all the EPROM Cells in a 1’s state

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