Step 9 of 11

Full ISR: toggle LED and reload Timer0

Goal

Complete the ISR: reload TMR0H/L, toggle LED on RB0, and see blinking in Proteus.

Between saving and restoring context: 1. Pause timer (BCF T0CON, TMR0ON) 2. Clear TMR0IF and reload TMR0H/L with same values from step 4 3. Restart timer (BSF T0CON, TMR0ON) 4. Toggle LED with BTFSC LATB,0 / BSF or BCF

Main loop stays at GOTO bucle — shows no polling needed.

Follow these steps

Complete isr_alta with the final file below (or add toggle + reload to step 7 skeleton).
Build, generate .HEX, load in Proteus (LED on RB0, 20 MHz).
Press Play and wait ~2 s: LED must toggle on/off.
If no blink: check GIE, TMR0IE, vector 0x0008, and TMR0IF cleared.

Your file so far

						        LIST    P=18F4550
        #include <P18F4550.INC>

        CONFIG  FOSC = HS
        CONFIG  WDT = OFF
        CONFIG  LVP = OFF
        CONFIG  PBADEN = OFF

        ORG     0x0000
        GOTO    inicio

        ORG     0x0008            ; alta prioridad (08H)
        GOTO    isr_alta

        ORG     0x0018            ; baja prioridad (18H)
        GOTO    isr_baja

        CBLOCK  0x20
temp_w
temp_status
        ENDC

init_gpio:
        BCF     TRISB, 0      ; RB0 salida (LED)
        BCF     LATB, 0
        RETURN

init_timer0:
        MOVLW   B'00000111'    ; 16 bit, interno, PS 1:256
        MOVWF   T0CON
        MOVLW   B'01100111'
        MOVWF   TMR0H
        MOVLW   B'01101010'
        MOVWF   TMR0L
        RETURN

isr_alta:
        BTFSS   INTCON, TMR0IF
        GOTO    fin_isr

        ; guardar contexto minimo
        MOVWF   temp_w
        SWAPF   STATUS, W
        MOVWF   temp_status

        BCF     T0CON, TMR0ON
        BCF     INTCON, TMR0IF
        MOVLW   B'01100111'    ; recarga Timer0 (~2 s)
        MOVWF   TMR0H
        MOVLW   B'01101010'
        MOVWF   TMR0L
        BSF     T0CON, TMR0ON

        ; toggle LED en RB0
        BTFSC   LATB, 0
        GOTO    apagar_led
        BSF     LATB, 0
        GOTO    restaurar
apagar_led:
        BCF     LATB, 0

restaurar:
        SWAPF   temp_status, W
        MOVWF   STATUS
        MOVF    temp_w, W
fin_isr:
        RETFIE

isr_baja:
        RETFIE

inicio:
        CALL    init_gpio
        CALL    init_timer0
        BCF     INTCON, TMR0IF
        BSF     INTCON, TMR0IE
        BSF     INTCON, GIE
        BSF     T0CON, TMR0ON
bucle:
        GOTO    bucle

        END

Checklist before you continue

ISR reloads Timer0 and toggles the LED.
**I saw the LED blink** in Proteus or hardware (~2 s per change).
Main loop does not read TMR0IF — confirms interrupt, not polling.

I completed this step