title  "Flash - Flash an LED on an off"
 
; Mark Crosbie  8/22/98  mark@mastincrosbie.com
;
;  The Program simply sets up Bit 0 of Port "A" to Output and then
;  loops, setting the value alternatively low and high
;
;  Hardware Notes:
;   Reset is tied through a 4.7K Resistor to Vcc and PWRT is Enabled
;   A 220 Ohm Resistor and LED is attached to PORTA.0 and Vcc
;
  LIST P=16C84, R=DEC
  errorlevel 0,-305
  INCLUDE "\mpasm\P16C84.inc"
 
;  Registers
Temp    equ     12              ;  16 Bit Dlay Variable
 
 __CONFIG _CP_OFF & _WDT_OFF & _XT_OSC & _PWRTE_ON
 
  PAGE
;  Mainline of Flash
 
  org 0
 
  clrf   PORTA                  ;  Clear all the Bits in Port "a"
  clrf   STATUS
  bsf    STATUS, RP0            ;  Goto Bank 1 to set Port Direction
  bcf    TRISA, 0               ;  Set RA0 to Output
  bcf    STATUS, RP0            ;  Go back to Bank 0
 
Loop
  movlw 1                       ;  Turn on the LED on Port A
  movwf PORTA                   ;
 
  call   Dlay                   ;  Delay Before Changing Values
 
  movlw 0                       ;  Turn off the LED on Port A
  movwf PORTA                   ;
 
  call   Dlay                   ;  Delay Before Changing Values
  goto Loop
 
;  Dlay Routine - Delay a Half Second before Returning
 
Dlay
 
 ifndef  Debug                  ;  If Debug NOT Defined
  movlw  0                      ;  Actual Setup the Delay Value
  movwf  Temp
  movlw  128
  movwf  Temp + 1
 else                           ;  If Debug Defined
  movlw  2                      ;  Programming Debug Delay Value
  movwf  Temp
  movlw  1
  movwf  Temp + 1
 endif
 
D_Loop                          ;  Loop Around Here until Complete
  decf   Temp                   ;  Decrement the lo Value
  btfsc  STATUS, Z              ;  Is the Zero Flag Set?
   decf  Temp + 1
  movf   Temp, w                ;  Are we At Zero for Both?
  iorwf  Temp + 1, w
  btfss  STATUS, Z
   goto  D_Loop
 
  return
 
  end