TS80C51RA2 Atmel Corporation, TS80C51RA2 Datasheet - Page 50

• Manufacturer Part Number: TS80C51RA2
• Description: High Performance 8-bit Microcontroller
• Manufacturer: Atmel Corporation

TS83C51RB2/RC2/RD2 ROM
ROM Structure
ROM Lock System
Signature bytes
Verify Algorithm
50
Encryption Array
Program Lock Bits
TS8xC51Rx2
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, 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 30. will provide different level of pro-
tection for the on-chip code and data.
Table 30. Program Lock bits
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.
Refer to Section “Verify algorithm”.
Security
level
the code array:16/32/64 Kbytes.
the encryption array:64 bytes.
the signature array:4 bytes.
1
2
3
Program Lock Bits
LB1
U
U
P
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.
4188A–8051–10/02