TS87C52X2 ATMEL Corporation, TS87C52X2 Datasheet - Page 31

• Manufacturer Part Number: TS87C52X2
• Description: 8-bit Microcontroller 8 Kbytes Otp
• Manufacturer: ATMEL Corporation

TS80C52X2
ROM Structure
ROM Lock System
Encryption Array
Signature bytes
Verify Algorithm
4184E–8051–09/02
Program Lock Bits
The TS80C52X2 ROM memory is divided in three different arrays:
•
•
•
The program Lock system, when programmed, protects the on-chip program against
software piracy.
Within the ROM array are 64 bytes of encryption array that are initially unprogrammed
(all FF’s). Every time a byte is addressed during program verify, 6 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 encrypted verify byte. The algorithm, with the
encryption array in the unprogrammed state, will return the code in its original, unmodi-
fied form.
When using the encryption array, one important factor needs to be considered. If a byte
has the value FFh, verifying the byte will produce the encryption byte value. If a large
block (>64 bytes) of code is left unprogrammed, a verification routine will display the
content of the encryption array. For this reason all the unused code bytes should be pro-
grammed with random values. This will ensure program protection.
The lock bits when programmed according to Table 19. will provide different level of pro-
tection for the on-chip code and data.
Table 19. Program Lock bits
U: unprogrammed
P: programmed
The TS80C52X2 contains 4 factory programmed signatures bytes. To read these bytes,
perform the process described in section 9.
Refer to Section “Verify Algorithm”.
Security
level
the code array:8 Kbytes.
the encryption array:64 bytes.
the signature array:4 bytes.
1
2
Program Lock Bits
LB1
U
P
LB2
U
U
LB3
U
U
Protection Description
No program lock features enabled. Code verify will still be
encrypted by the encryption array if programmed. MOVC instruction
executed from external program memory returns non encrypted
data.
MOVC instruction executed from external program memory are
disabled from fetching code bytes from internal memory, EA is
sampled and latched on reset.
TS8xCx2X2
31