AT83C5111 datasheet(68/86 Pages) ATMEL

68 / 86 page

AT8xC5111

4190A–8051–11/02

ROM

ROM Structure

The AT83C511 ROM memory is divided in three different arrays:

•

The code array: ................................................................................4K Bytes

•

The encryption array: .......................................................................64 bytes

•

The signature array:..........................................................................4 bytes

•

ROM Lock System

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

software piracy.

Encryption Array

Within the ROM array there are 64 bytes of encryption array. 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, creat-

ing 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 pro-

grammed with random values.

Configuration Byte

The configuration byte is a special register. Its content, described in paragraph

Section “Registers”, page 10 is defined by the diffusion mask in the ROM version or writ-

ten by the OTP programmer in the OTP version.

The lock bits when programmed according to Table 55 will provide different levels of

protection for the on-chip code and data.

Notes:

1. U: unprogrammed

2. P: programmed

*Warning: When security bit is set, ROM contend cannot be verified. Only the CRC is verified.

Signature Bytes

The T80C5111 contains 4 factory programmed signatures bytes. To read these bytes,

perform the process described in Section “Signature Bytes Content”, page 69.

Verify Algorithm

Refer to Section “Verify Algorithm”, page 68.

Program Code Mapping

As there is no external capability in LPC packages, the code size is limited to 4K Bytes.

Any access above 4K will be mapped in the first 4K segment (0XXXh).

Table 1. Program Lock Bits

Program Lock Bits

Protection Description

Security

Level

LB1

LB2

No program lock features enabled. Code verify will still be encrypted by the encryption array if

programmed. MOVC instruction returns non encrypted data.

Same as 1

Same as 2, also verify is disabled.

This security level is available because ROM integrity will be verified thanks to another method*.

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