AT80C51RA2-RLSIV datasheet(51/86 Pages) ATMEL

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4188F–8051–01/08

AT/TS8xC51Rx2

TS83C51RB2/RC2/RD2 ROM

8.1

ROM Structure

The TS83C51RB2/RC2/RD2 ROM memory is divided in three different arrays:

• the code array:16/32/64 Kbytes.

• the encryption array:64 bytes.

• the signature array:4 bytes.

8.2

ROM Lock System

The program Lock system, when programmed, protects the on-chip program against software

piracy.

8.2.1

8.2.1 Encryption Array

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.

8.2.2

Program Lock Bits

The lock bits when programmed according to Table 8-1. will provide different level of protection

for the on-chip code and data.

U: unprogrammed

P: programmed

8.2.3

Signature bytes

The TS83C51RB2/RC2/RD2 contains 4 factory programmed signatures bytes. To read these

bytes, perform the process described in section 8.3.

Table 8-1.

Program Lock bits

Program Lock Bits

Protection Description

Security

level

LB1

LB2

LB3

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.

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