;**********************************************************************
list p=16f870
#include p16f870.inc>

; __CONFIG _CP_OFF _WDT_ON _BODEN_ON _PWRTE_ON _RC_OSC _WRT_ENABLE_ON _LVP_OFF _CPD_OFF

FLAG EQU 0x20
Var1 EQU 0x21
Var2 EQU 0x22

INT_Var1 EQU 0x30
INT_Var2 EQU 0x31

W_Temp EQU 0x72
STATUS_Temp EQU 0x73
FSR_Temp EQU 0x74

#define VAL_1MS .248

#define FLAG_INC 0
#define FLAG_DEC 1

org 0x00 ; RESET  0x000
nop
clrf PCLATH
goto Main

org 0x004
INT_ISRs
;***************************************************************
movwf W_Temp ; save off current W register contents
movf STATUS,W ; move status register into W register
bcf STATUS,RP0 ; ensure file register bank set to 0
movwf STATUS_Temp ; save off contents of STATUS register
movf FSR,W
movwf FSR_Temp

BANKSEL PORTB
movf PORTB,W
bcf INTCON,RBIF
bcf INTCON,RBIE ; RBIE Disable

call Bounce_Delay

btfsc PORTB,4
goto Check_DEC_KEY

bsf FLAG,FLAG_INC ; FLAG_INC  1
goto Exit_ISRs

Check_DEC_KEY
btfss PORTB,5
bsf FLAG,FLAG_DEC

Exit_ISRs
movf FSR_Temp,W
movwf FSR
bcf STATUS,RP0 ; ensure file register bank set to 0
movf STATUS_Temp,w ; retrieve copy of STATUS register
movwf STATUS ; restore pre-isr STATUS register contents
swapf W_Temp,F
swapf W_Temp,W ; restore pre-isr W register contents
retfie ; return from interrupt

;******************************************************************************
;**** Delay 10 ms 
;******************************************************************************
Bounce_Delay
movlw .10
movwf INT_Var1

Bounce_Loop1
movlw .248
movwf INT_Var2
Bounce_Loop2
nop
decfsz INT_Var2,F
goto Bounce_Loop2
decfsz INT_Var1,F
goto Bounce_Loop1
return

******************************************
Main

BANKSEL TRISB
movlw B'11110000'
movwf TRISB ; RB4..RB7
clrf TRISC
movlw B'00000000' ; Enable PORTB  Pull UP
movwf OPTION_REG

BANKSEL PORTB
movlw B'11111111'
movwf PORTB
clrf PORTC

bsf INTCON,GIE
clrf FLAG
bsf FLAG,FLAG_INC

Prog_Loop
btfss FLAG,FLAG_INC
goto Dec_Process

Inc_Process
call Delay_50ms
incfsz PORTC,F
goto Inc_Process
goto SLEEP_Process

Dec_Process
call Delay_50ms
decfsz PORTC,F
goto Dec_Process

SLEEP_Process
clrf PORTC
clrf FLAG
movf PORTB,W
bcf INTCON,RBIF
bsf INTCON,RBIE
SLEEP
nop
nop
goto Prog_Loop

;****************************************************************************
;**** Delay 50ms 
;****************************************************************************
Delay_50ms
movlw .50
movwf Var2
Delay_200ms_Loop
call Delay_1ms
decfsz Var2,F
goto Delay_200ms_Loop
return

;****************************************************************************
;**** Delay 1ms 
;****************************************************************************
Delay_1ms
nop
nop
nop
movlw VAL_1MS
movwf Var1
Delay_1ms_Loop nop
decfsz Var1,F
goto Delay_1ms_Loop
return

END