IS80LV52 Datasheet, PDF (39/48 Pages) Integrated Silicon Solution, Inc – CMOS SINGLE CHIP LOW VOLTAGE 8-BIT MICROCONTROLLER

IS80LV52
IS80LV32
ROM Lock System
The program lock system, when programmed, protects
the ROM code against software piracy. The IS80LV52/32
has a two-level program lock system (see Table 14) and
a 32-byte encryption table. No matter what lock bit is, the
user submits the encryption table with his or her code in
verify ROM mode. Both the lock-bit and encryption array
ISSI ^®
Encryption Array
Within the ROM array are 32 bytes of Encryption Array
that are initially unprogrammed (all 1's). Every time that a
byte is addressed during verify, five address lines are
used to select a byte of the Encryption 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 unprogrammed state (all 1's), will return the
code in its original, unmodified form.
When using the encryption array, one important factor
needs to be considered. If a code byte has the value
0FFH, verifying the byte will produce the encryption byte
value. If a large block (> 32 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 programmed with some
value other than 0FFH, and not all of them the same value.
Table 14. Program Lock Bits
LB1
LB2
1
U
U
2
P
U
3
P
P
Protection Type
No Program Lock Features enabled. (Code verify will still be
encrypted by the Encryption Array if Programmed)
MOVC instructions executed from external program memory
are diabled form fetching code bytes from internal memory,
EA is sampled and latched on Reset.
Same as 2, also ROM verify is disabled.
Integrated Silicon Solution, Inc. — 1-800-379-4774
39
ADVANCE INFORMATION MC019-0A
10/01/98