TS80C51RA2-VCKB datasheet(51/74 Pages) ATMEL

51 / 74 page

Rev. C - 06 March, 2001

TS80C51RA2/RD2

TS83C51RB2/RC2/RD2

TS87C51RB2/RC2/RD2

7. TS83C51RB2/RC2/RD2 ROM

7.1. 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.

7.2. ROM Lock System

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

7.2.1. 7.2.1. 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.

7.2.2. Program Lock Bits

The lock bits when programmed according to Table 28. will provide different level of protection for the on-chip

code and data.

U: unprogrammed

P: programmed

7.2.3. Signature bytes

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

process described in section 8.3.

7.2.4. Verify Algorithm

Refer to 8.3.4.

Table 28. 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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