User Manual

41
T89C51AC2
Rev. B – 19-Dec-01
10.2 Boot Process
10.2.1 Software boot proce ss
examp le
Many algorithms can be used for the soft w are boot proces s . Before describing the m,
W e give be low the desc r iption of the different fl ags and bytes.
Boot Loader Jump Bit (BLJB):
- This bit indicat es if on RESET the user wants to jump to this application at address
@ 0000h on FM0 or execute the boot load er at addres s @ F800h on FM 1.
- B LJ B = 0 on parts delivered with bootloader programmed.
- To read or modify this bit, the APIs are used.
Boot Vector Address (SBV):
- This byte cont ains the MSB of the us er boot loader address in FM0.
- The defaul t value of S BV is FFh (no user boot loader in FM 0).
- To read or modify this byte, the API s are used.
Extra Byte (EB) & Boot Status Byte (BSB ):
- These bytes are reserved for customer use.
- To read or modify these byt es , the APIs are used.
10.2.2 Hardware boot process At the falling e dge of RESET, th e bit EN BOOT in AUXR1 register i s initialized with the
value of Boot Loader Jump Bit (BLJB).
Further at the falling edge of RE SET if the following c onditions (called Hardware c ondi-
tion) are detec ted:
• PSEN low,
• EA high,
• ALE high (or not connected).
– After Hardware Condition t he FCON register is initialized with the value 00h
and the P C is initialized with F800h (F M1).
The Hardware condition m ak es the bootloader t o be executed, whatever BLJB v alue is.
If no hardware condition is det ected, the FCON register is ini tia lized with the v alue F0h.
Chec k of the BL JB value.
•IfbitBLJB=1:
User application in FM0 will be started at @0000h (s tandard r es et ).
•IfbitBLJB=0:
Boot load er will be started at @F800h in FM1.