Microcontroller Systems Exam

    #INCLUDE "P16F84A.INC"

    __CONFIG _XT_OSC & _WDT_OFF & _PWRTE_ON & _CP_OFF

    ERRORLEVEL -302

    ;----------------------------------------------------------
    ;   variable declaration
    COUNTERA    EQU H'10'
    COUNTERB    EQU H'11'
    COUNTER     EQU H'12'
    CONFIG_ADDR EQU H'13'
    VAL         EQU H'14'

    ORG     0x00
    GOTO    START

    ORG     0x04
    GOTO    ON_INT

START
    ;----------------------------------------------------------
    ;   register configurations

    ;----------I/O Configurations------------------------------
    BSF     STATUS, RP0
    MOVLW   0x00
    MOVWF   TRISA

    MOVLW   B'00000001'
    MOVWF   TRISB
    ;----------End of I/O Configurations-----------------------

    ;----------Counter Configurations--------------------------
    MOVLW   0x07
    MOVWF   OPTION_REG
    ;----------End of Counter Configurations-------------------

    ;----------Interrupt Configurations------------------------
    BCF     STATUS, RP0
    BSF     INTCON, GIE
    BSF     INTCON, INTE
    ;BSF        STATUS, RP0
    ;----------End of Interrupt Configurations-----------------

    ;----------General Initialization--------------------------
    CLRF    PORTA
    CLRF    PORTB
    ;----------End of General Initialization-------------------

RESTART                 ;   start of the counter, initializes
    MOVLW   0x00        ;   the port A to the first two values to
    MOVWF   PORTA       ;   display
    CALL    DELAY

    MOVLW   0x01
    MOVWF   COUNTER

COUNT
    ;---------------------------------------------------------
    ;   loop of the program
    MOVF    COUNTER, W  ;   the counter decrements and will be displayed
    MOVWF   PORTA       ;   to the port A
    CALL    DELAY

    INCF    COUNTER, F

    MOVF    COUNTER, W

    XORLW   0x0A        ;   once it reaches A... not 9 (since i need to display 9)
    BTFSS   STATUS, Z   ;   skip the count and restart

    GOTO    COUNT
    GOTO    RESTART

DELAY
    ;---------------------------------------------------------
    ;   create a delay
    MOVLW   D'1'
    MOVWF   COUNTERA

LOOPA
    CALL    DELAYA
    DECFSZ  COUNTERA, 1
    GOTO    LOOPA
    RETLW   0x00

DELAYA
    MOVLW   D'15'
    MOVWF   COUNTERB

LOOPB
    CALL    DELAYB
    DECFSZ  COUNTERB, 1
    GOTO    LOOPB
    RETLW   0x00

DELAYB
    CLRF     TMR0
    BCF     INTCON, T0IF

LOOPC
    BTFSS   INTCON, T0IF
    GOTO     LOOPC
    RETLW    0x00

ON_INT
    BSF     PORTB, 1
    BCF     INTCON, INTF

ON_STORE_DATA
    ;   EEPROM initialization
    BCF     STATUS, RP0
    CLRF    EEADR
    CLRF    EEDATA

    MOVLW   0x00
    MOVWF   CONFIG_ADDR
    MOVWF   EEADR

    MOVF    COUNTER, W      ;   put the value of the counter to working register
    MOVWF   EEDATA          ;   then put the value to the EEPROM Data

    BSF     STATUS, RP0

    BCF     INTCON, GIE

    BSF     EECON1, WREN    ;   write the data to the EEPROM
    MOVLW   0x55            ;   according to the data sheet
    MOVWF   EECON2
    MOVLW   0xAA
    MOVWF   EECON2
    BSF     EECON1, WR

    BSF     INTCON, GIE

    ;   verify the data after storing it
ON_VERIFY_DATA
    BCF     STATUS, RP0

    MOVLW   0x00            ;   initialize the address where the
    MOVWF   EEADR           ;   EEPROM will read (address 0x00)

    BSF     STATUS, RP0

    BCF     EECON1, WREN
    BCF     EECON1, WR
    BSF     EECON1, RD

    BCF     STATUS, RP0
    MOVF    EEDATA, W
    MOVWF   VAL

    RRF     VAL, F          ;   rotate the value of the VAL variable
    RRF     VAL, F          ;   4 times to produce the output to the
    RRF     VAL, F          ;   4 most significant bits
    RRF     VAL, F
    RRF     VAL, F

    MOVF    VAL, W
    MOVWF   PORTB

INT_LOOP                    ;   stops the execution of the countdown
    MOVF    COUNTER, W      ;   by looping until the switch is
    MOVWF   PORTA           ;   turned on again
    BTFSC   PORTB, 0
    GOTO    COUNT
    GOTO    ON_INT

    END