Datasheet

4
4266C–CAN–03/08
AT89C51CC03 UART Bootloader
Security The bootloader has Software Security Byte (SSB) 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, BSB and SBV.
The Bootloader returns an error message.
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 error message.
Only a full chip erase command can reset the software security bits.
Software Boot
Vector
The Software Boot Vector (SBV) forces the execution of a user bootloader starting at address
[SBV]00h in the application area (FM0).
The way to start this user bootloader is described in the section “Boot Process”.
Level 0 Level 1 Level 2
Flash/EEPROM 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 Read only access allowed All access not 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
UART Bootloader
Application
User Bootloader
[SBV]00h
FM1
FM0