at89c51snd1 ATMEL Corporation, at89c51snd1 Datasheet - Page 4

• Manufacturer Part Number: at89c51snd1
• Description: Mp3 Microcontrollers
• Manufacturer: ATMEL Corporation

Software Security Byte
Software Boot Vector
4
AT89C51SND1 UART Bootloader
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
Software Security Bit” can only write a higher priority level. There are three levels of
security:
•
•
•
Only a full-chip erase command can reset the software security bits.
Table 3. Software Security Byte Levels
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 “Regular Boot Process”,
page 7.
Flash
Fuse bit
BSB & SBV
SSB
Manufacturer info Read only access allowed
Bootloader info
Erase block
Full chip erase
Blank Check
level 0: NO_SECURITY (FFh)
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)
This is the default level.
Level 2 forbids all read and write accesses to/from the Flash memory.
The bootloader returns an error message.
Level 0
Any access allowed
Any access allowed
Any access allowed
Any access allowed
Read only access allowed
Allowed
Allowed
Allowed
Level 1
Read only access allowed
Read only access allowed
Read only 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
All access not allowed
Read only access allowed
Read only access allowed
Read only access allowed
Not allowed
Allowed
Allowed
4241B–MP3–07/04