AT89C5131A View Datasheet(PDF) - Atmel Corporation
Part Name
Description
Manufacturer
AT89C5131A Datasheet PDF : 34 Pages
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Mapping and Default
Value of Hardware
Security Byte
The 4 MSB of the Hardware Byte can be read/written by software (this area is called Fuse bits).
The 4 LSB can only be read by software and written by hardware in parallel mode (with parallel
programmer devices).
Bit Position Mnemonic Default Value Description
7
X2B
U
To start in x1 mode
6
BLJB
P
To map the boot area in code area between F800h-FFFFh
5
OSCON1
U
Oscillator control (bit 1)
4
OSCON0
U
Oscillator control (bit 0)
3
reserved
U
2
LB2
P
1
LB1
U
To lock the chip (see datasheet)
0
LB0
U
Note: U: Unprogrammed = 1
P: Program = 0
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.
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.
Level 0
Flash/EEPROM Any access allowed
Fuse bit
Any access allowed
BSB & SBV & EB Any access allowed
SSB
Any access allowed
Manufacturer info Read only access allowed
Bootloader info Read only access allowed
Erase block
Allowed
Full chip erase Allowed
Blank Check
Allowed
Level 1
Read only access allowed
Read only access allowed
Any access allowed
Write level2 allowed
Read only access allowed
Read only access allowed
Not allowed
Allowed
Allowed
Level 2
All access not allowed
All access not allowed
Any access allowed
Read only access allowed
Read only access allowed
Read only access allowed
Not allowed
Allowed
Allowed
4 AT89C5131A USB Bootloader
4287E–USB–04/08
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