8XL52 Datasheet, PDF (17/20 Pages) Intel Corporation – LOW VOLTAGE CHMOS SINGLE-CHIP 8-BIT MICROCONTROLLERS

8XL52 54 58
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 V_PP from V_CC to 12 75V g0 25V
5 Pulse ALE PROG 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
Figure 11 Programming Signals Waveforms
272468 – 19
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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