Hardware Bytes
Table 23. HSB Byte – Hardware Security Byte
7
6
5
-
4
-
3
-
2
1
0
X2B
BLJB
LB2
LB1
LB0
Bit
Bit
Number
Mnemonic Description
X2 Bit
7
6
X2B(1)
BLJB(2)
-
Program this bit to start in X2 mode.
Unprogram (erase) this bit to start in standard mode.
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.
Reserved
5 - 4
The value read from these bits is always unprogrammed. Do not program these
bits.
Reserved
3
-
The value read from this bit is always unprogrammed. Do not program this bit.
Hardware Lock Bits
Refer to for bits description.
2 - 0
LB2:0
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, AT89C51SND2C products
are delivered with BLJB programmed.
3. Bits 0 to 3 (LSN) can only be programmed by hardware mode.
Table 24. SBV Byte – Software Boot Vector
7
6
5
4
3
2
1
0
ADD15
ADD14
ADD13
ADD12
ADD11
ADD10
ADD9
ADD8
Bit
Bit
Number
Mnemonic Description
MSB of the user’s boot loader 16-bit address location
Refer to the boot loader datasheet for usage information (boot loader dependent)
7 - 0
ADD15:8
Reset Value = XXXX XXXX, UUUU UUUU after an hardware full chip erase.
Table 25. SSB Byte – Software Security Byte
7
6
5
4
3
2
1
0
SSB7
SSB6
SSB5
SSB4
SSB3
SSB2
SSB1
SSB0
Bit
Bit
Number
Mnemonic Description
Software Security Byte Data
Refer to the boot loader datasheet for usage information (boot loader dependent)
7 - 0
SSB7:0
Reset Value = XXXX XXXX, UUUU UUUU after an hardware full chip erase.
22
AT8xC51SND2C
4341D–MP3–04/05
ATMEL [ ATMEL ]
