Micro Sys. Lab 6 Ex. 02 - Simple Input

    #INCLUDE "P16F84A.INC"

    __CONFIG _XT_OSC & _WDT_OFF & _PWRTE_ON & _CP_OFF

    ERRORLEVEL -302

    ORG 0x00
    GOTO START

    ORG 0x04
    GOTO START

START
    ;----------------------------------------------------------
    ;   register configurations
    BSF STATUS, RP0
    MOVLW 0xFF
    MOVWF TRISA
    MOVLW 0x00
    MOVWF TRISB

    MOVLW 0x07
    MOVWF OPTION_REG

    BCF STATUS, RP0
    CLRF PORTA
    CLRF PORTB

MAIN
    MOVLW B'11111111'
    MOVWF PORTB

S1
    BTFSC PORTA, 0
    GOTO MAIN
    GOTO L2

S2
    BTFSC PORTA, 1
    GOTO S1
    BTFSC PORTA, 0
    GOTO MAIN
    GOTO L4

S3
    BTFSC PORTA, 2
    GOTO S2
    BTFSC PORTA, 1
    GOTO S1
    BTFSC PORTA, 0
    GOTO MAIN
    GOTO L6

S4
    BTFSC PORTA, 3
    GOTO S3
    BTFSC PORTA, 2
    GOTO S2
    BTFSC PORTA, 1
    GOTO S1
    BTFSC PORTA, 0
    GOTO S1
    GOTO L8

L2
    MOVLW B'11111100'
    MOVWF PORTB
    GOTO S2

L4
    MOVLW B'11110000'
    MOVWF PORTB
    GOTO S3

L6
    MOVLW B'11000000'
    MOVWF PORTB
    GOTO S4

L8
    MOVLW B'00000000'
    MOVWF PORTB
    GOTO S4

    END