Datasheet

59
AT89C51AC3
4383D–8051–02/08
Hardware Security Byte Table 24. Hardware Security Byte
Default value after erasing chip: FFh
Notes: 1. Only the 4 MSB bits can be accessed by software.
2. The 4 LSB bits can only be accessed by parallel mode.
7 6 5 4 3 2 1 0
X2B BLJB - - - LB2 LB1 LB0
Bit
Number
Bit
Mnemonic Description
7 X2B
X2 Bit
Set this bit to start in standard mode
Clear this bit to start in X2 mode.
6 BLJB
Boot Loader JumpBit
- 1: To start the user’s application on next RESET (@0000h) located in FM0,
- 0: To start the boot loader(@F800h) located in FM1.
5-3 -
Reserved
The value read from these bits are indeterminate.
2-0 LB2:0 Lock Bits