Datasheet

22
AT8xC51SND1C
4109E–8051–06/03
Hardware Bytes Table 22. HSB Byte – Hardware Security Byte
Reset Value = XXUU UXXX, UUUU UUUU after an hardware full chip erase.
Note: 1. X2B initializes the X2 bit in CKCON during the reset phase.
2. In order to ensure boot loader activation at first power-up, AT89C51SND1C products
are delivered with BLJB programmed.
3. Bits 0 to 3 (LSN) can only be programmed by hardware mode.
Reset Value = XXXX XXXX, UUUU UUUU after an hardware full chip erase.
Reset Value = XXXX XXXX, UUUU UUUU after an hardware full chip erase.
76543210
X2B BLJB - - - LB2 LB1 LB0
Bit
Number
Bit
Mnemonic Description
7X2B
(1)
X2 Bit
Program this bit to start in X2 mode.
Unprogram (erase) this bit to start in standard mode.
6BLJB
(2)
Boot Loader Jump Bit
Program this bit to execute the boot loader at address F000h on next reset.
Unprogram (erase) this bit to execute user’s application at address 0000h on
next reset.
5 - 4 -
Reserved
The value read from these bits is always unprogrammed. Do not program these
bits.
3-
Reserved
The value read from this bit is always unprogrammed. Do not program this bit.
2 - 0 LB2:0
Hardware Lock Bits
Refer to for bits description.
Table 23. SBV Byte – Software Boot Vector
76543210
ADD15 ADD14 ADD13 ADD12 ADD11 ADD10 ADD9 ADD8
Bit
Number
Bit
Mnemonic Description
7 - 0 ADD15:8
MSB of the user’s boot loader 16-bit address location
Refer to the boot loader datasheet for usage information (boot loader dependent)
Table 24. SSB Byte – Software Security Byte
76543210
SSB7SSB6SSB5SSB4SSB3SSB2SSB1SSB0
Bit
Number
Bit
Mnemonic Description
7 - 0 SSB7:0
Software Security Byte Data
Refer to the boot loader datasheet for usage information (boot loader dependent)