8 Bit Up Down Counter

This project shows the application of PIC microcontroller as an up/down counter, designed to count from 0 to FF and vice versa. To simulate circuit in this project, initially activate Mixed Mode simulator from the Schematic Editor window. Simulation can be performed by selecting Run Transient analysis from Simulation menu.

This circuit uses a PIC Microcontroller, Binary to Seven Segment Decoder/Driver, Seven Segment LED Display. In this circuit, Port A of PIC Microcontroller is assigned as the Input Port while Port B is assigned as Output Port. Port A is used for selecting whether the counter works as Up Counter or as Down Counter. When the LSB of Port A is high then the circuit works as an Up Counter else as Down Counter. Binary to Seven Segment Decoder decodes the data from Port B to 7-segment format, which are displayed in 7-segment displays. The count sequence appears at the LED display in 7-segment form.

The source code written in Assembly language can be viewed from the code editor window

The program is as shown:

include "p16c5x.inc"

startup code

org 0

start nop

org 10

clrf FSR ; clearing FSR register

clrf INDF ; clearing INDF register

clrw ; clearing W register

comf INDF,0 ; complimenting INDF register

tris PORTA ; setting PORTA in input mode

btfss PORTA,0 ; 0 for Down counting & 1 for Up counting

false call d_cnt ; call D_CNT subroutine

true call up_cnt ; call UP_CNT subroutine

; Up counting starts here

up_cnt

clrf fsr ; clearing FSR register

clrf indf ; clearing INDF register

clrw ; clearing W register

tris portb ; setting PORTB in output mode

movlw 0x00 ; moving literal constant 0x00 to W

movwf 08h ; moving the content of W to 08H

rep1

movwf portb ; moving the content of W through PORTB

incf 08h,1 ; incrementing the content of 08H

movf 08H,0 ; moving the content of 08H to W

goto rep1 ; repeating the loop REP1

; Down counting starts here

d_cnt clrf fsr ; clearing FSR register

clrf indf ; clearing INDF register

clrw ; clearing W register

tris PORTB ; setting PORTB in output mode

movlw 0xff ; setting the start value

movwf 08H ; moving the content of W to 08H

rep2

movwf PORTB ; moving the content of W through PORTB

decf 08H,1 ; decrementing the value of 08H

movf 08H,0 ; moving the content of 08H to W

goto REP2 ; repeating the loop REP2

retlw start

end ; directive 'end of program'

The source code in the code editor window has to be compiled after making any modifications

(editing). Also the code can be debugged during simulation.