Potentiometer input programming activity
Create the Input program
The entire INPUT.ASM program is shown below. INPUT reads the state of two of the CHRP pushbuttons and outputs a unique pattern for each button on the LEDs. Start a new project in MPLAB, copy the INPUT.ASM code into the project, and build the program.
;INPUT-POT.ASM v2.0 Last modified on August 3, 2010 ;=============================================================================== ;Description: Senses potentiometer input digitally. ;Start of MPLAB and processor configuration. include "p16f676.inc" ;Include processor definitions __config _CPD_OFF & _CP_OFF & _BODEN_OFF & _MCLRE_ON & _PWRTE_ON & _WDT_OFF & _INTRC_OSC_NOCLKOUT ;End of MPLAB and processor configuration. ;Start of hardware equates. P1 equ 4 ;Potentiometer P1 Port A bit position org 3FFh ;Oscillator calibration location oscillator org 00h ;Start of program memory bsf STATUS,RP0 ;Select memory register page 1 call oscillator ;Store pre-programmed oscillator calibration movwf OSCCAL ;constant in OSCCAL register goto init ;Start program after Interrupt vector org 05h ;Continue after interrupt vector init ;Initialize ports A and C for digital I/O bcf STATUS,RP0 movlw 7 ;Disable comparator and make movwf CMCON ;RA0-2 digital I/O banksel ANSEL ;Switch to register bank 1 movlw 11010111b ;Disable Port A pull-ups, set TMR0 to movwf OPTION_REG ;internal clock with prescaler 256 clrf ANSEL ;Set all PORTA pins to digital movlw 11011111b ;Set RA5 as output and all movwf TRISA ;other PORTA pins as inputs clrf TRISC ;Set all PORTC pins as outputs banksel PORTC ;Return to PORTC register bank clrf PORTA ;Turn off phototranstor LED clrf PORTC ;Turn all LEDs off checkP1 btfsc PORTA,P1 ;Check if P1 is low or high goto P1On ;If high, turn high LEDs on movlw 00110000b ;If low, turn low LEDs on movwf PORTC goto checkP1 ;Check again P1On movlw 00001111b ;Turn high LEDs on movwf PORTC goto checkP1 ;Check again end
Download the program into the CHRP and verify its operation.
