;File incdec.asm - Blinks LEDs on PORTB outputs in a sequential pattern.
;Configuration - RC oscillator, watchdog timer off, power-up timer enabled.
processor 16f84A
include <p16f84A.inc>
__config _RC_OSC &_WDT_OFF &_PWRTE_ON
;Declare variables at two memory locations
J equ H'1F' ;J stored at hex address 1F.
K equ H'1E' ;K stored at hex address 1E.
;Program
org 0 ;Start program at address zero.
;Set PORTB as output and initialize it.
movlw B'00000000' ;Move 8 binary zeros to the W (working) register
tris PORTB ;Sets all of the pins of PORTB as outputs
movlw B'00011'
tris PORTA ;Sets all of the pins of PORTA
movlw B'00000000'
movwf PORTB ;Turns off all of the outputs of PORTB
;Scan input switches.
SCAN 
btfsc PORTA,0 ;Skip INCREMENT if PORTA pin 0 is low
call INCREMENT
;btfsc PORTA,0 ;Skip WAIT if PORTA pin 0 is low
;call WAIT
btfsc PORTA,1 ;Skip DECREMENT if PORTA pin 1 is low
call DECREMENT
;btfsc PORTA,1 ;Skip WAIT if PORTA pin 1 is low
;call WAIT
goto SCAN ;Check switches again.
;Increment output
INCREMENT 
incf PORTB
btfss PORTB,3 ;Skip return if PORTB pin 3 is high
return
btfss PORTB,1 ;Skip return if PORTB pin 1 is high
return
movlw B'00000000' ;The number 10 was found so reset to 0
movwf PORTB ;clear PORTB
return
;Decrement output
DECREMENT 
decf PORTB
btfss PORTB,3 ;Skip return if PORTB pin 3 is high
return
btfss PORTB,2 ;Skip return if PORTB pin 2 is high
return
btfss PORTB,1 ;Skip return if PORTB pin 1 is high
return
btfss PORTB,0 ;Skip return if PORTB pin 0 is high
return
movlw B'00001001' ;The number 0 was found so reset to 9
movwf PORTB ;
return
;Wait until the button is released (we want to count button presses)
WAIT 
LOOK 
btfsc PORTA,0 ;Skip if PORTA pin 0 is low
goto LOOK
btfsc PORTA,1 ;Skip if PORTA pin 1 is low
goto LOOK
return

end