Hi everyone.  The following is my first attempt at a program.  I built the
NOPPP and everything looks great.  I am using a 20mghz ceramic resonator and
my breadboard circuit is crude.  All IO are open except for the RB4 to which
I have connected an LED.  It flashes every 16 seconds for 2 seconds.  The
MPLAB simulator runs as planned - Flash every 8 seconds for one.

I would welcome any comments on code style, technique etc. as well.

Thanks for your time...

        LIST P=PIC16F84A, R=d
        __config H'3FFA'

#include "p16f84a.inc"

ScratchPadRam   EQU     0x20
TMR0            EQU     H'01'
STATUS          EQU     H'03'
#DEFINE         RB4     4
;--------------------------------------------------------------------------
; Variables
;--------------------------------------------------------------------------
        cblock  0x0C
                timer_lo        ;LSB for period counter
                timer_hi        ;MSB for period counter
                Seconds         ;seconds
                Minutes         ;minutes 0-59
                Hours           ;hours
                Quant1          ;number of counts for feeder 1
                Quant2          ;number of counts for feeder 2
                Quant3          ;number of counts for feeder 3
                Quant4          ;number of counts for feeder 4
                DispenCnt       ;int? input from counter
        endc

;--------------------------------------------------------------------------
;Start of ROM
;--------------------------------------------------------------------------

                ORG     0
                GOTO    Start

;----------------------------------------
;Interrupt Service Routine
;----------------------------------------
                ORG     0x04
Intsvc
                clrwdt                  ;clear watchdog timer to ensure startup
                bcf     INTCON,2        ;clear interrupt flag before return
                incf    timer_lo,f      ;increment LSByte
                btfsc   STATUS,Z        ;zero set means overflow
                incf    timer_hi,f      ;increment MSByte
                movlw   H'4B'           ;LSB tweak factor 4996891
                xorwf   timer_lo,w      ;compare
                btfss   STATUS,Z        ;are they the same?
                retfie                  ;nope go back
                movlw   H'4C'           ;MSB tweak factor
                xorwf   timer_hi,w      ;compare
                btfss   STATUS,Z        ;are they the same?
                retfie                  ;nope go back
                incf    Seconds,f       ;increment seconds finally
                rlf     PORTB,f         ;every 7 seconds portb4 should flash
                clrf    timer_lo        ;clear LSB
                clrf    timer_hi        ;clear MSB
                movlw   H'3C'           ;get ready to check for a minute
                xorwf   Seconds,w       ;compare
                btfss   STATUS,Z        ;are they the same?
                retfie                  ;nope go back
                incf    Minutes,f       ;yes-add a minute
                clrf    Seconds         ;clear Seconds - at 60
                movlw   H'3C'           ;get ready to check for an hour
                xorwf   Minutes,w       ;compare
                btfss   STATUS,Z        ;are they the same?
                retfie                  ;nope go back
                incf    Hours,f         ;yes - another hour
                clrf    Minutes         ;clear Minutes - at 60
                movlw   H'18'           ;check for hour roll
                xorwf   Hours,w         ;compare
                btfss   STATUS,Z        ;are they the same?
                retfie                  ;not yet midnight
                clrf    Hours           ;it is midnight
                retfie                  ;return from interrupt

Timer_init
                bcf     INTCON, 2
                bsf     INTCON, 7
                bsf     INTCON, 5
                clrf    TMR0
                clrwdt
                movlw   b'11011000'
                option
                clrf    TMR0
                retlw   0

Port_Init
                BCF STATUS, RP0         ;
                CLRF PORTB              ; Initialize PORTB
                BSF STATUS, RP0         ; Select Bank 1
                MOVLW H'00'             ; Value used to
                MOVWF TRISB             ; Set RB<3:0> as inputs RB<5:4> as outputs RB<7:6> as inputs

Start
                call Timer_init
Loop:           nop
                nop
                goto Loop
                end

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