TS87C51RD2 ATMEL Corporation, TS87C51RD2 Datasheet - Page 51

• Manufacturer Part Number: TS87C51RD2
• Description: (TS8xC51Rx2) High Performance 8-bit Microcontroller
• Manufacturer: ATMEL Corporation

8. TS83C51RB2/RC2/RD2 ROM
8.1
8.2
8.2.1
8.2.2
8.2.3
4188E–8051–08/06
ROM Structure
ROM Lock System
8.2.1 Encryption Array
Signature bytes
Program Lock Bits
The TS83C51RB2/RC2/RD2 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, 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.
The lock bits when programmed according to Table 8-1. will provide different level of protection
for the on-chip code and data.
Table 8-1.
U: unprogrammed
P: programmed
The TS83C51RB2/RC2/RD2 contains 4 factory programmed signatures bytes. To read these
bytes, perform the process described in section 8.3.
• the code array:16/32/64 Kbytes.
• the encryption array:64 bytes.
• the signature array:4 bytes.
Security
level
1
2
3
Program Lock Bits
LB1
Program Lock bits
U
P
U
LB2
U
U
P
LB3
U
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.
Same as level 1+ Verify disable.
This security level is only available for 51RDX2 devices.
AT/TS8xC51Rx2
51