Simple Counter with PIC16F877A

Config Proteus like this

And here is the source code

;; -----------------------------------------------------------------------------
;; File name: 7SegmentsLedx4_Counter.asm
;; Email: dmtmd2010@yahoo.com.vn
;; Blog: tdmblogging.blogspot.com
;; Date: March 3rd, 2014
;; Description: a simple counter from 0000 to 9999 using PIC16F877A and 7 segments leds.
;; -----------------------------------------------------------------------------

include P16F877A.inc

; define constants

num_0 equ  20
num_1 equ  21
num_2 equ  22
num_3 equ  23

time_delay  equ  24
time_delay1  equ  25
time_delay2  equ  26

counter  equ  27
rate  equ  28
tmp   equ  29


org 0
goto 100

org 10
table ; look up for 7 segments code
movfw counter
addwf PCL
retlw H'3F'  ; 0
retlw H'06'  ; 1
retlw H'5B'  ; 2
retlw H'4F'  ; 3
retlw H'66'  ; 4
retlw H'6D'  ; 5
retlw H'7D'  ; 6
retlw H'07'  ; 7
retlw H'7F'  ; 8
retlw H'6F'  ; 9

org 100
start
; config and init ports
bsf  STATUS, 5    ; select bank 1

clrw
movwf TRISB    ; mark port B as an output port
movwf TRISC    ; mark port C as an output port

bcf  STATUS, 5    ; select bank 0

clrf PORTB
clrf num_0
clrf num_1
clrf num_2
clrf num_3
clrf rate

movlw H'FF'
movwf PORTC

; main program start here
loop
; control the counting speed
incf rate   ; increase rate
btfsc rate, 6   ; if rate equals 01000000
call incNum0   ; do count
btfsc rate, 6   ; and then clear rate
clrf rate

call display   ; scan the leds
goto loop


display
bsf  PORTC, 0   ; port C equals 11111111

movf num_0, w   ; look for the 7 segments code of num_0 value
movwf counter
call table
movwf PORTB   ; display to port B
bcf  PORTC, 3   ; port C equals 11110111
call delay

bsf  PORTC, 3

movf num_1, w
movwf counter
call table
movwf PORTB
bcf  PORTC, 2
call delay

bsf  PORTC, 2

movf num_2, w
movwf counter
call table
movwf PORTB
bcf  PORTC, 1
call delay

bsf  PORTC, 1

movf num_3, w
movwf counter
call table
movwf PORTB
bcf  PORTC, 0
call delay
return

incNum0
incf num_0   increase num_0
; test if num_0 equals 10 (1010 in binary)
clrf tmp
btfsc num_0, 1   ; xxxxxx1x
bsf  tmp, 0
btfsc num_0, 3   ; xxxx1xxx
incf tmp
btfsc tmp, 1
call incNum1   ; num_0 = 10 -> increase the next
return

incNum1
clrf num_0
incf num_1
clrf tmp
btfsc num_1, 1
bsf  tmp, 0
btfsc num_1, 3
incf tmp
btfsc tmp, 1
call incNum2
return

incNum2
clrf num_1
incf num_2
clrf tmp
btfsc num_2, 1
bsf  tmp, 0
btfsc num_2, 3
incf tmp
btfsc tmp, 1
call incNum3
return

incNum3
clrf num_2
incf num_3
clrf tmp
btfsc num_3, 1
bsf  tmp, 0
btfsc num_3, 3
incf tmp
btfsc tmp, 1
clrf num_3
return

;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;
;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;
delay
movlw H'5'
movwf time_delay2
delay3
movlw H'5'
movwf time_delay1
delay2
movlw H'5'
movwf time_delay
delay1
decfsz time_delay
goto delay1
decfsz time_delay1
goto delay2
decfsz time_delay2
goto delay3
return

END