prog20.asm

主要是8051源代码

;  PROG20 - Do a Debounce on a button and Toggle an LED
;
;  This Application polls the button and toggles the LED
;   State when the button is pressed (and has been "Debounced").
;
;  The button is assumed to be debounced if it does not change 
;   state for 20 msecs.  
;
;  Myke Predko
;  98.02.20
;
;  Hardware Notes:
;  80C520 Running at 1 MHz
;  P1.0 is the LED (to light, it is pulled down)
;  P1.1 is connected to a Momentary ON Switch that Pulls down the Line.

;  Variable Declarations
;  Just "A" and "B" are used for this program.  

;  Mainline
 org 0                          ;  Execution Starts Here

Loop:                           ;  Loop Here Forever

PressWait:			;  Wait for the Button to be Pressed
  jb	 P1.1,PressWait

  mov	 A,#191			;  Setup 20 msec Delay
  mov	 B,#10

PressDebounce:			;  Now, See if the Button is Held down
  jb	 P1.1,PressWait		;   20 msec - If Released, Start Delay Over
  djnz	 ACC,PressDebounce	
  djnz	 B,PressDebounce

;  #### - Button Press is Debounced

  cpl	 P1.0			;  Toggle the LED State

ReleaseWait:			;  Now, Wait for the Button to be Released
  jnb	 P1.1,ReleaseWait

  sjmp	 Loop