P87C511 datasheet(18/21 Pages) INTEL

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87C5180C51BH80C31BH

272335 – 22

For compatibility 25 pulses may be used

Figure 11 Programming Waveforms

PROGRAMMING ALGORITHM

Refer to Table 4 and Figures 10 and 11 for address

data and control signals set up To program the

87C51 the following sequence must be exercised

1 Input the valid address on the address lines

2 Input the appropriate data byte on the data lines

3 Activate the correct combination of control sig-

nals

4 Raise EA VPP from VCC to 1275V g025V

5 Pulse ALEPROG 5 times for the EPROM array

and 25 times for the encryption table and the lock

bits

Repeat 1 through 5 changing the address and data

for the entire array or until the end of the object file is

reached

Program Verify

Verification may be done after programming either

one byte or a block of bytes In either case a com-

plete verify of the array will ensure reliable program-

ming of the 87C51

The lock bits cannot be directly verified Verification

of the lock bits is done by observing that their fea-

tures are enabled

ROM and EPROM Lock System

The program lock system when programmed pro-

tects the onboard program against software piracy

The 80C51BH has a one level program lock system

and a 64-byte encryption table 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 encryp-

tion table The 87C51 has a 3-level program lock

system and a 64-byte encryption array Since this is

an EPROM device all locations are user-program-

mable 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 lf 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

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