;
; primer programa ASM del PIC
; Sebastia, 14 de Abril de 2008.
;
; Conectar el pin 5 (RA3) a R=1 K cap al Anode del LED.
; XTAL 4 MHz entre pin 13 i 14.
; 2x C (22pf) del pin 13 i 14 a massa.

;    list p=16f452
    #include    <p18f452.inc>

; Configuration bits :
;
;    Oscillator mode := XT ;
;    Watch Dog Timer := off ;
;    Low Voltage Programming := on :

    config    WDT=OFF
    config    OSC=XT

; User data

; MYDATA    UDATA
;
;DTEMP    res    1        ; reserve 1 address location
;DFLAG    res    1        ;

 CBLOCK        0x020
    DTEMP            ;
    DFLAG            ;
    BsrTemp          ; copy of BSR
    StatusTemp       ; copy of STATUS
    WregTemp         ; copy of WREG
 ENDC

DFL0    equ    0x00        ; define constant : set flag bit = 0 bit of DFLAG.

; +++ code start

MYCODE    CODE

    org     0x0000               ; Reset vector
    goto    Start                ; skip interrupt vectors

    org        0x0008            ; High Priority Interrupt Vector

    bcf        T0CON,TMR0ON      ; T0CON bit 7 off => stops timer 0
    bcf        INTCON,TMR0IF     ; clear timer has overflowed flag
    bcf        DFLAG, DFL0       ; clear soft (own) flag

    retfie    FAST               ; return from interrupt - pop W,STATUS & BSR off the stack

    org        0x0018                ; Low Priority Interrupt Vector

    goto    ISR_space

    org        0x0040

ISR_space

    movff    STATUS, StatusTemp    ; save STATUS register
    movff    WREG, WregTemp        ; save WREG
    movff    BSR, BsrTemp            ; save BSR register

; low priority code

    movff    BsrTemp,BSR            ; restore BSR
    movff    WregTemp, WREG        ; restore working register
    movff    StatusTemp, STATUS    ; restore STATUS register

    retfie                ; return from interrupt

    org        0x0100        ; Program start

Start

;    banksel CONFIG1H
;    movlw    0x21                ; XT mode
;    movwf    CONFIG1H

    banksel    TRISB                ; select TRIS bank
    clrf       TRISB                ; clear TRISB =>set PORTB as Outputs.
    clrf       PORTB                ; clear PORT B data
    clrf       TRISA                ; clear TRISA => set PORTA as Output.
    clrf       PORTA                ; clear PORT A (output) data => set LOW.

    banksel    INTCON               ; select INTCON bank
    bsf        INTCON, GIE          ; enable Global Interrupts
    bsf        INTCON, TMR0IE       ; set INTCON bit 5 => enable Timer 0 interrupt

Bucle

    movlw      0x55              ; odd pins HIGH, even pins LOW
    movwf      PORTA             ; set port A data

    call       Delay1            ; use 1 or 2 ...

    movlw      0xAA              ; even pins HIGH, odd pins LOW
    movwf      PORTA             ; set port A data

    call       Delay2            ; use 2 or 1 ...

    goto    Bucle

; own subroutines

Delay1

    movlw        0xF0            ; set Timer0 value
    movwf        TMR0L            ; 0x00 = longest, 0xFF = shortest delay.

    clrf            DFLAG            ;
    bsf            DFLAG, DFL0    ; set flag bit

    movlw        0xC8            ; (7) enable, (6) 8-bit, (5) internal, (4) low-to-high, (3) noprescaler, (2-1-0) prescaler value
    movwf        T0CON            ; start Timer0

Tloop

    btfsc        DFLAG, DFL0    ; wait for overflow (bit test, skip if clear)
    goto        Tloop            ; after interrupt, DFL0  = 0.

    return                        ; end of Delay1
;

Delay2

    movlw        0xFF            ; set DTEMP value
    movwf        DTEMP            ; 0x00 = shortest, 0xFF = longest delay

Dloop

    decfsz        DTEMP, F        ; use countdown to create delay (decrement, skip if Zero)
    goto        Dloop            ; end loop when DTEMP = 0
    return

szID
    DB    0x55, 0x55, 0xAA, 0xAA    ; eye catcher.
    DT    "22/04/2008, v 1.2a"        ; RETLW 8-bit.
    DB    0x55, 0x55, 0xAA, 0xAA    ; eye catcher.

    end