TS87C52X2 ATMEL Corporation, TS87C52X2 Datasheet - Page 32

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

TS87C52X2
EPROM Structure
EPROM Lock System
Encryption Array
Program Lock Bits
Signature Bytes
32
TS8xCx2X2
The TS87C52X2 is divided in two different arrays:
•
•
In addition a third non programmable array is implemented:
•
The program Lock system, when programmed, protects the on-chip program against
software piracy.
Within the EPROM array are 64 bytes of encryption array that are initially unpro-
grammed (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,
unmodified 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 three lock bits, when programmed according to Table 1., will provide different level
of protection for the on-chip code and data.
U: unprogrammed
P: programmed
WARNING: Security level 2 and 3 should only be programmed after EPROM and Core
verification.
The TS80/87C52X2 contains 4 factory programmed signatures bytes. To read these
bytes, perform the process described in section 9.
Security
level
the code array: 8 Kbytes
the encryption array: 64 bytes
the signature array: 4 bytes
1
2
3
4
Program Lock Bits
LB1
U
P
U
U
LB2
U
U
P
U
LB3
U
U
U
P
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, and further programming of the
EPROM is disabled.
Same as 2, also verify is disabled.
Same as 3, also external execution is disabled.
4184E–8051–09/02