PIC18F14K22. MPLab. Выбор источника прерывания

LIST    p=18F14k22
    #include    p18f14k22.inc
    #define tfov    .219    ; Time for timer overflow
    #define atsfrb  0x010   ; Adress to save first received byte
    #define in_pin  RA0
    #define in_port PORTA
 
    CONFIG  FOSC = HS
    CONFIG  PLLEN = OFF
    ;CONFIG PCLKEN = ON ; Primary Clock Enable bit
    ;CONFIG IESO = ON   ; Internal/External Oscillator switchover bit
    CONFIG  PWRTEN = OFF
    CONFIG  WDTEN = OFF ; Watchdog Timer Enable bit
    ;CONFIG HFOFST = OFF    ; HFINTOSC Fast Start-up bit
    CONFIG  MCLRE = OFF
    CONFIG  STVREN = OFF    ; Stack full/underflow will not cause Reset
 
    num         equ 01h 
    time_value  equ 02h ; Need for keeping tfov
    res_stat    equ 04h ; Received status
    byte_point  equ 05h ; Point to byte to write
    start_bit   equ 0
    fbr     equ 1   ; Indicator: first byte have received
 
    ORG     0x0
    GOTO        main
 
; ------------------MAIN INTERRUPT, CLEAR TIMER-------------------
    ORG     0x8
    MOVFF       time_value, TMR0L
; Need for clear RABIF flag ------------------
    MOVF        PORTB, W,  ACCESS
    BCF     INTCON, RABIF
; -------------------------------------------------------
    RETFIE
; ------------------------------------------------------------------------------------
 
; ------------------SECONDARY INTERRUPT, WRITING -------------
    ORG 0x18        ; Secondary interrupt, output
    BTFSS   res_stat, start_bit ; Check the start bit, skip if set
    GOTO    set_start
    GOTO    write_byte
 
set_start
    BTFSC   in_port, in_pin ; If in_pin=0 skip start_bit clear
    BSF res_stat, start_bit
    NOP
    NOP
    NOP
    NOP
    NOP
    NOP
    NOP
    NOP
    NOP
    NOP
    NOP
    NOP
    GOTO    exit
 
; Begin writing byte
write_byte
    BTFSS   in_port, in_pin
    GOTO    set_0
    GOTO    set_1
set_0
    BCF INDF0, 0
    MOVLW   6
    CPFSGT  num     ; Compare f with WREG, skip >
    GOTO    shift_value ; Shift out value if the last bit not written
    GOTO    lbw     ; Last bit have written
set_1
    BSF INDF0, 0
    MOVLW   6
    CPFSGT  num     ; Compare f with WREG, skip >
    GOTO    shift_value ; Shift out_value if the last bit not written
    GOTO    lbw     ; Last bit have written
shift_value
    RLNCF   INDF0       ; Rotate Left f (No Carry)
    INCF    num
    GOTO    exit
lbw ; Last bit writing
    CLRF    num
    BCF res_stat, start_bit
    BSF res_stat, fbr   ; With this instruction time to exec on 1 cycles more
    GOTO    exit
; End writing byte
 
exit
    MOVFF   time_value, TMR0L
    BCF INTCON, TMR0IF  ; Clear interrupt flag (TMR0)
    RETFIE
; ------------------------------------------------------------------------------------
 
main
    BCF INTCON, GIE ; Disable all interrupts
; I/O setting
    CLRF    ANSEL       ; Set PORTA as digital
    CLRF    ANSELH      ; Set PORTB as digital  
    MOVLW   0xFF
    MOVWF   TRISA       ; Set PORTA on input
    MOVWF   TRISB       ; Set PORTB on input
    CLRF    TRISC       ; Set PORTC on output
; Interrupt settings
    BSF RCON, IPEN  ; Enable priority levels on interrupts
    MOVLW   b'01101000' ; Interrupt on change PORTA/B and TMR0
    MOVWF   INTCON
    MOVLW   b'10000001' ; bit-7 -  PORTA and PORTB pull-ups are disabled
                                                                           ; bit-2 = 0 - Low priority of TMR0 Overflow Interrupt
    MOVWF   INTCON2     ; bit-0 - High priority RA and RB Port Change Interrupt
    MOVLW   0xFF    
    MOVWF   IOCA        ; Interrupt-on-change enabled for PORTA
    CLRF    IOCB        ; Interrupt-on-change disabled for PORTB
; Timer0 settings
    MOVLW   b'01001000' ; bit-7 - TMR0ON=0 - Stops Timer0
    MOVWF   T0CON       ; bit-6 - T08BIT=1 - Configured as an 8-bit timer
                ; bit-5 - T0CS=0 - Internal instruction cycle clock
                ; bit-4 - T0SE=1 - Increment on l-h transition on T0CKI
                ; bit-3 - PSA=0 - Timer0 prescaler is NOT assigned
                ; bit-2:0 - Timer0 Prescaler Select bits
; Initialization
    CLRF    num
    CLRF    res_stat
    CLRF    byte_point
    MOVLW   tfov
    MOVWF   time_value
    MOVFF   time_value, TMR0L
    MOVLW   atsfrb      ; Adress to save first received byte
    MOVWF   FSR0L
 
    BSF T0CON, TMR0ON   ; Enables Timer0
    BSF INTCON, GIE ; Enable all interrupts
 
loop
    BTFSC   res_stat, fbr   ; Skip is first bit haven't received
    MOVFF   INDF0, LATC ; Send received byte on PORTC
    GOTO    loop
END