4

4256B–USB–03/06

AT89C5132

Security

The bootloader has Software Security Byte (SSB see Table 7) to protect itself from user access

or ISP access.

The Software Security Byte (SSB) protects from ISP accesses. The command ’Program Soft-

ware Security Bit’ can only write a higher priority level. There are three levels of security:

•

Level 0: NO_SECURITY (FFh)

This is the default level.

From level 0, one can write level 1 or level 2.

•

Level 1: WRITE_SECURITY (FEh)

In this level it is impossible to write in the Flash memory.

The Bootloader returns an err_WRITE status.

From level 1, one can write only level 2.

•

Level 2: RD_WR_SECURITY (FCh)

Level 2 forbids all read and write accesses to/from the Flash memory.

The Bootloader returns an err_WRITE or an err_VENDOR status.

Only a full chip erase command can reset the software security bits.

Table 3. Security Levels

Level 0

Level 1

Level 2

Flash

Any access allowed

Read only access allowed

All access not allowed

Fuse bit

Any access allowed

Read only access allowed

All access not allowed

BSB & SBV & EB

Any access allowed

Any access allowed

Any access allowed

SSB

Any access allowed

Write level2 allowed

Read only access allowed

Manufacturer info

Read only access allowed

Read only access allowed

Read only access allowed

Bootloader info

Read only access allowed

Read only access allowed

Read only access allowed

Erase block

Allowed

Not allowed

Not allowed

Full chip erase

Allowed

Allowed

Allowed

Blank Check

Allowed

Allowed

Allowed