AT89C51RC2-3CSCM(2003) 查看數據表（PDF） - Atmel Corporation
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AT89C51RC2-3CSCM Datasheet PDF : 125 Pages
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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
Any access allowed
Read only access allowed Any access not allowed
Fuse Bit
Any access allowed
Read only access allowed Any access not allowed
BSB & SBV
Any access allowed
Read only access allowed Any access not allowed
SSB
Any access allowed
Write level 2 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
94 AT89C51RB2/RC2
4180B–8051–04/03
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