at89c51rd2-smsum ATMEL Corporation, at89c51rd2-smsum Datasheet - Page 103

• Manufacturer Part Number: at89c51rd2-smsum
• Description: 8-bit Flash Microcontroller
• Manufacturer: ATMEL Corporation

24.8
24.8.1
24.8.2
4235J–8051–01/08
Functional Description
Software Security Bits (SSB)
Full Chip Erase
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:
This is the default level.
From level 0, one can write level 1 or level 2.
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.
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 soft-
ware security bits.
From level 2, one cannot read and write anything.
Table 24-7.
The ISP command "Full Chip Erase" erases all user Flash memory (fills with FFh) and sets
some bytes used by the bootloader at their default values:
• level 0: NO_SECURITY (FFh)
• level 1: WRITE_SECURITY (FEh)
• level 2: RD_WR_SECURITY (FCh
Manufacturer Info
• BSB = FFh
Flash/EEPROM
Full Chip Erase
Bootloader Info
Blank Check
BSB & SBV
Erase Block
Fuse Bit
SSB
Software Security Byte Behavior
Read-only access allowed
Read-only access allowed
Any access allowed
Any access allowed
Any access allowed
Any access allowed
Allowed
Allowed
Allowed
Level 0
Read-only access allowed
Read-only access allowed
Read-only access allowed
Read-only access allowed
Read-only access allowed
Write level 2 allowed
Not allowed
Allowed
Allowed
Level 1
AT89C51RD2/ED2
Read-only access allowed
Read-only access allowed
Read-only access allowed
Any access not allowed
Any access not allowed
Any access not allowed
Not allowed
Level 2
Allowed
Allowed
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