AT80C51RA2-3CSCV View Datasheet(PDF) - Atmel Corporation
Part Name
Description
MFG CO.
'AT80C51RA2-3CSCV' PDF : 86 Pages View PDF
AT/TS8xC51Rx2
9. TS87C51RB2/RC2/RD2 EPROM
9.1 EPROM Structure
The TS87C51RB2/RC2/RD2 EPROM is divided in two different arrays:
• the code array:16/32/64 Kbytes.
• the encryption array:64 bytes.
In addition a third non programmable array is implemented:
• the signature array: 4 bytes.
9.2 EPROM Lock System
The program Lock system, when programmed, protects the on-chip program against software
piracy.
9.2.1
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, cre-
ating 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.
9.2.2
Program Lock Bits
The three lock bits, when programmed according to Table 9-1.9.2.3, will provide different level of
protection for the on-chip code and data.
Table 9-1. Program Lock bits
Program Lock Bits
Security
level
LB1 LB2 LB3 Protection Description
No program lock features enabled. Code verify will still be
1
U
U
U
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
2
P
U
U
disabled from fetching code bytes from internal memory, EA is
sampled and latched on reset, and further programming of the
EPROM is disabled.
3
U
P
U Same as 2, also verify is disabled.
4
U
U
P Same as 3, also external execution is disabled.
U: unprogrammed,
P: programmed
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4188F–8051–01/08
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