87L52 datasheet(17/20 Pages) INTEL

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8XL525458

PROGRAMMING ALGORITHM

Refer to Table 3 and Figures 10 and 11 for address

data and control signals set up To program the

87L5X 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 OTP ROM

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

Program verify may be done after each byte or block

of bytes is programmed In either case a complete

verify of the programmed array will ensure reliable

programming of the 8XL5X

The lock bits cannot be directly verified Verification

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

tures are enabled

272468 – 19

Figure 11 Programming Signals Waveforms

ROM and OTP ROM Lock System

The 87L5X program lock system

when pro-

grammed protects the onboard program against

software piracy

The 80L5X has a one-level program lock system and

a 64-byte encryption table See line 2 of Table 4 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 fac-

tory 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 87L5X has a 3-level program lock system and a

64-byte encryption array Since this is an OTP ROM

device all locations are user-programmable See

Table 4

Encryption Array

Within the OTP ROM array are 64 bytes of Encryp-

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

Every time that a byte is addressed during a verify 6

address lines are used to select a byte of the En-

cryption 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 3 (Programming the

OTP ROM)

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

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