Functional Description
Software Security Bits (SSB)
The SSB protects any Flash access from ISP command.
The command "Program Software 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 )
For this level it is impossible to write in the Flash memory, BSB and SBV.
The Bootloader returns ’P’ on write access.
From level 1, one can write only level 2.
•
level 2: RD_WR_SECURITY (FCh
The level 2 forbids all read and write accesses to/from the Flash/EEPROM memory.
The Bootloader returns ’L’ on read or write access.
Only a full chip erase in parallel mode (using a programmer) or ISP command can reset
the software security bits.
From level 2, one cannot read and write anything.
Table 71. Software Security Byte Behavior
Level 0
Level 1
Level 2
Flash/EEPROM
Fuse Bit
Any access allowed
Any access allowed
Any access allowed
Any access allowed
Read only access allowed
Read only access allowed
Read only access allowed
Write level 2 allowed
Any access not allowed
Any access not allowed
Any access not allowed
Read only access allowed
BSB & SBV
SSB
Manufacturer
Info
Read only access allowed
Read only access allowed
Read only access allowed
Bootloader Info
Erase Block
Read only access allowed
Allowed
Read only access allowed
Not allowed
Read only access allowed
Not allowed
Full-chip Erase
Blank Check
Allowed
Allowed
Allowed
Allowed
Allowed
Allowed
96
AT89C51RB2/RC2
4180E–8051–10/06
ATMEL [ ATMEL ]
