Datasheet

21
4341H–MP3–10/07
AT8xC51SND2C/MP3B
6.4.2 Hardware Condition Boot Mapping
The hardware condition is based on the ISP pin. When driving this pin to low level, the chip reset
sets ENBOOT and forces the reset vector to F000h instead of 0000h in order to execute the
boot loader software.
As shown in Figure 6-4 the hardware condition always allows in-system recovery when user’s
memory has been corrupted.
6.4.3 Programmed Condition Boot Mapping
The programmed condition is based on the Boot Loader Jump Bit (BLJB) in HSB. As shown in
Figure 6-4 when this bit is programmed (by hardware or software programming mode), the chip
reset set ENBOOT and forces the reset vector to F000h instead of 0000h, in order to execute
the boot loader software.
Figure 6-4. Hardware Boot Process Algorithm
The software process (boot loader) is detailed in the “Boot Loader Datasheet” Document.
6.5 Preventing Flash Corruption
See Section “Reset Recommendation to Prevent Flash Corruption”, page 48.
Atmel’s
Boot Loader
HardwareSoftware
Hard Cond?
ISP = L?
RESET
Hard Cond Init
ENBOOT = 1
PC = F000h
FCON = 00h
Prog Cond?
BLJB = P?
Standard Init
ENBOOT = 0
PC = 0000h
FCON = F0h
Prog Cond Init
ENBOOT = 1
PC = F000h
FCON = F0h
User’s
Application
Process Process