TS87C51RC2 ATMEL Corporation, TS87C51RC2 Datasheet - Page 52

• Manufacturer Part Number: TS87C51RC2
• Description: High Performance 8-bit Microcontroller 32 Kbytes Otp
• Manufacturer: ATMEL Corporation

TS80C51RA2/RD2
TS83C51RB2/RC2/RD2
TS87C51RB2/RC2/RD2
8. TS87C51RB2/RC2/RD2 EPROM
8.1. EPROM Structure
The TS87C51RB2/RC2/RD2 EPROM is divided in two different arrays:
In addition a third non programmable array is implemented:
8.2. EPROM Lock System
The program Lock system, when programmed, protects the on-chip program against software piracy.
8.2.1. Encryption Array
Within the EPROM 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, 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 programmed with random values. This will ensure program protection.
8.2.2. Program Lock Bits
The three lock bits, when programmed according to Table 29.8.2.3. , 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.
8.2.3. Signature bytes
The TS87C51RB2/RC2/RD2 contains 4 factory programmed signatures bytes. To read these bytes, perform the
process described in section 8.3.
52
Security level
the code array: . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 16/32/64 Kbytes.
the encryption array: . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 64 bytes.
the signature array: . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4 bytes.
1
2
3
4
Program Lock Bits
LB1
U
U
U
P
LB2
U
U
U
P
LB3
U
U
U
P
Table 29. Program Lock bits
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.
Protection description
Rev. C - 06 March, 2001