TP87C51FA-33 Просмотр технического описания (PDF) - Intel

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TP87C51FA-33

CHMOS SINGLE-CHIP 8-BIT MICROCONTROLLERS

Intel 

8XC51FX

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 lf 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 87C51FX has 3 programmable lock bits that

when programmed according to Table 5 will provide

different 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 87C51FX has 3 signature bytes in locations

30H 31H and 60H The 83C51FA has 2 signature

bytes in locations 30H and 31H 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

83C51FA

87C51FA

83C51FB

87C51FB

83C51FC

87C51FC

Contents

89H

58H

7AH FAH

FAH

7BH FBH

FBH

7CH FCH

FCH

Erasure Characteristics (Windowed

Packages Only)

Erasure of the EPROM begins to occur when the

chip is exposed to light with wavelength shorter than

approximately 4 000 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-sec cm Exposing the

EPROM to an ultraviolet lamp of 12 000 mW cm rat-

ing for 30 minutes at a distance of about 1 inch

should be sufficient

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

18

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