Hello, all

I have got a question, see following code first.

; interrupt vectors:


ORG 00h
AJMP Reset ; RESET start


ORG 03h
LJMP Intr0 ; external INT_0 (comms test)


ORG 0Bh
LJMP Timr0 ; TIMER_0 (timeout)


ORG 13h
LJMP Intr1 ; external INT_1 (RTC wakeup)


ORG 1Bh
RETI ; TIMER_1 (not used)


ORG 23h
RETI ; UART (not used)


ORG 30h ; start of program


;------------- MAIN PROGRAM -------------
;
; restart on comms int (INT_0) in manual mode


SDIReset:
MOV SP,#Stack ; force stack pointer
AJMP Res_T ; goto reset testing


; start on power up - after RESET (delay = 3ms)


Reset:
MOV SP,#Stack ; stack pointer
MOV PCON,#00h ; UART mode /2 SMOD=0
MOV SCON,#50h ; serial port mode 1, REN=1
MOV TMOD,#21h ; timer_1 in mode 2 (8-bit auto reload internal control timer)


( ignored )



Intr0: MOV DPTR,#SDIReset ; INT_0 int - comms detection in manual mode
PUSH DPL ; restart the system
PUSH DPH
CLR EX0 ; dissable INT_0
RETI



My question is when the program starts from "SDIReset" which is at the address 30h ?
So far, my knowledge is that program simply jumps to the place labeled with "Reset:"
only due to the hardware reset or power on,. I can not figure out in what case
program jumps to "SDIReset".


I realize that "SDIReset" only appears in two places, one is as label at address 30h,
another is in Intr0 (interrupt 0) service routine (see above code), where address of
SDIReset (30h) is passed to DPTR, then,How to force the program to jump to place
labeled "SDIReset" ? What I can not figure out is how Intr0 be able to force program
start from SDIReset ? thanks!


Daniel