prog25.asm

包括了各种常用的8051单片机的程序

;  PROG25 -  Timer Interrupt Handler without Context Saving 
;
;  This Application Decrements the Value in P1 Once Per Second
;
;  Myke Predko
;  98.03.01
;
;  Hardware Notes:
;  80C520 Running at 4 MHz
;  The 80C520's Clock will be running at 1/4 Second "Ticks"
;  P1 is Connected to a Set of LEDs
;  P3 is Connected to an External LED Diplay

;  Variable Declarations
;  R0 is Used as the Interrupt Count
;  R1/R2/R3 are Used for the External Display Count  

 org 0
  ajmp   Mainline

 org 0Bh                        ;  Timer0 (Real Time) Interrupt

  djnz  R0,IntSkip              ;  One Second Up?

  dec   P1                      ;  Decrement the Timer Display

  mov   R0,#15                  ;  Reset the Counter

IntSkip:

  reti

 org 020h                       ;  Program Mainline
Mainline:

  mov    R0,#15                 ;  Want to Change the Value once Every 4 Times

  mov    CKCON,#%00001000       ;  Use Internal /4 Clock for Timer0
  mov    TMOD,#%00000001        ;  Timer0 - Uses Internal Clock
                                ;         - Run in Mode 1
  mov    TCON,#%00010000        ;  Start Timer0 running

  mov    IE,#%10000010          ;  Enable the Timer 0 Interrupt

;  Now, Do the Looping Output

MainLoop:                       ;  Come Back Here After Decrementing P3

  mov    R1,#0                  ;  Setup for the Delay
  mov    R2,#0
  mov    R3,#4

DlayLoop:                       ;  Loop Here for Delays
  djnz   1,DlayLoop
  djnz   2,DlayLoop
  djnz   3,DlayLoop

  dec    P3                     ;  Decrement the LED Output

  ajmp   MainLoop               ;  Wait to Decrement the Next Time