;  外部中斷實驗
      LED    BIT P1.1
      LEDBuf BIT  0
       org     0000H
       ljmp    Start
       ORG     000BH
       LJMP    INTERRUPT
       org     0030H
INTERRUPT:
       push    PSW         ; 保護現場
       cpl     LEDBuf      ; 取反LED
       mov     c, LEDBuf
       mov     LED, c
       pop     PSW         ; 恢復現場

       reti

Start:
       clr     LEDBuf
       clr     LED
       mov     TCON, #01h  ; 外部中斷0下降沿觸發
       mov     IE, #81h    ; 打開外部中斷允許位(EX0)及總中斷允許位(EA)
OK:    ljmp    OK

       end