tsc251g1dxxx-l12ced ATMEL Corporation, tsc251g1dxxx-l12ced Datasheet - Page 41

• Manufacturer Part Number: tsc251g1dxxx-l12ced
• Description: 8/16-bit Microcontroller With Serial Communication Interfaces - 32kbytes Rom
• Manufacturer: ATMEL Corporation

Lock Bit System
Encryption Array
4135F–8051–11/06
The TSC87251G2D products implement 3 levels of security for User’s program as
described in Table 33. The TSC83251G2D products implement only the first level of
security.
Level 0 is the level of an erased part and does not enable any security features.
Level 1 locks the programming of the User’s internal Code Memory, the Configuration
Bytes and the Encryption Array.
Level 2 locks the verifying of the User’s internal Code Memory. It is always possible to
verify the Configuration Bytes and the Lock Bits. It is not possible to verify the Encryp-
tion Array.
Level 3 locks the external execution.
Table 33. Lock Bits Programming
Notes:
The security level may be verified according to Table 34.
Table 34. Lock Bits Verifying
Note:
The TSC83251G2D and TSC87251G2D products include a 128-byte Encryption Array
located in non-volatile memory outside the memory address space. During verification
of the on-chip code memory, the seven low-order address bits also address the Encryp-
tion Array. As the byte of the code memory is read, it is exclusive-NOR’ed (XNOR) with
the key byte from the Encryption Array. If the Encryption Array is not programmed (still
all 1s), the user program code is placed on the data bus in its original, unencrypted form.
If the Encryption Array is programmed with key bytes, the user program code is
encrypted and cannot be used without knowledge of the key byte sequence.
Level
0
1
2
3
1. Returns encrypted data if Encryption Array is programmed.
2. Returns non encrypted data.
3. x means don’t care. Level 2 always enables level 1, and level 3 always enables levels
1. x means don’t care.
1 and 2.
Lock bits
LB[2:0]
01x
1xx
000
001
(3)
(3)
Level
0
1
2
3
Execution
Internal
Enable
Enable
Enable
Enable
Execution
External
Disable
Enable
Enable
Enable
Verification
Enable
Enable
Disable
Disable
AT/TSC8x251G2D
(1)
(1)
Lock bits Data
Programming
xxxxx000
xxxxx001
xxxxx01x
xxxxx1xx
Disable
Disable
Disable
Enable
(1)
PROM read
External
(MOVC)
Enable
Disable
Disable
Disable
(2)
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