On Interrupt

[Mark]

I'm using a 16F628 and RB0

[mister_e]

here's something to play with.

    ' RB0 interrupt
    ' =============
    '
    ' File name : RB0.bas
    ' Company : Mister E 
    ' Programmer : Steve Monfette
    ' Date : 03/05/2005
    ' Device : PIC16F628


    '
    '    PIC setting
    '    ===========
         '
         ' Using MPASM to compile the code to target device
         '
         '
@ __config _INTRC_OSC_NOCLKOUT & _WDT_ON & _PWRTE_ON & _MCLRE_OFF & _LVP_OFF & _BODEN_ON 
         ' Internal Oscillator
         ' Enable watch dog timer
         ' Enable power up timer
         ' Disable MCLR pin
         ' Disable low voltage programming
         ' Enable brown out detect


    '
    '    Hardware definition
    '    ===================
         '
         '
         TRISB = %00000001   ' RB0 as input, other as output
                             ' Push button between RB0 & ground
    
    '
    '    I/O Alias definition
    '    ====================
         '
         '
         RB0LED              var   PORTB.6
         MainLoopLED         var   PORTB.7

         
    '
    '    Interrupt Definition
    '    ====================
         '
         '
         OPTION_REG = 0      ' Enable pull-up on PORTB
                             ' RB0 interrupt on falling edge
                             
         INTCON = %10010000  ' Enable Global interrupt
                             ' Enable RB0 interrupt

         on interrupt goto RB0Interrupt
         
    '
    '    Variable definition
    '    ===================
         '
         '
         Delay              var word
         
         
    '
    '    MainLoop
    '    ========
         '
         '
Start:
     ' Let's do some led blink on RB.7
     '
     '
    Toggle mainloopled
    for Delay = 1 to 500 ' delay loop 500ms
        pause 1          ' using 1 ms delay to avoid latency
        next             '
    goto start           ' do it forever
    
         
    Disable Interrupt
RB0Interrupt:
            ' RB0 interrupt subroutine
            '
            ' will toggle RB6 state everytime we get an interrupt
            '
            '
    Toggle rb0led
    while PORTB.0 = 0                ' wait untill RB0 go high 
    wend
    pause 50                         ' debounce delay
    INTCON.1 = 0                     ' Reset RB0 int flag
    resume                           ' return to main loop
    Enable interrupt

[mister_e]

and another way by polling interrupt flag.

    ' RB0 interrupt
    ' =============
    '
    ' File name : RB0.bas
    ' Company : Mister E 
    ' Programmer : Steve Monfette
    ' Date : 03/05/2005
    ' Device : PIC16F628


    '
    '    PIC setting
    '    ===========
         '
         ' Using MPASM to compile the code to target device
         '
         '
@ __config _INTRC_OSC_NOCLKOUT & _WDT_ON & _PWRTE_ON & _MCLRE_OFF & _LVP_OFF & _BODEN_ON 
         ' Internal Oscillator
         ' Enable watch dog timer
         ' Enable power up timer
         ' Disable MCLR pin
         ' Disable low voltage programming
         ' Enable brown out detect


    '
    '    Hardware definition
    '    ===================
         '
         '
         TRISB = %00000001   ' RB0 as input, other as output
                             ' Push button between RB0 & ground
    
    '
    '    I/O Alias definition
    '    ====================
         '
         '
         RB0LED              var   PORTB.6
         MainLoopLED         var   PORTB.7

         
    '
    '    Interrupt Definition
    '    ====================
         '
         '
         OPTION_REG = 0      ' Enable pull-up on PORTB
                             ' RB0 interrupt on falling edge
                             

    '
    '    Variable definition
    '    ===================
         '
         '
         Delay              var word
         
         
    '
    '    MainLoop
    '    ========
         '
         '
Start:
     '
     '
    Toggle mainloopled
    for Delay = 1 to 500    ' delay loop 500ms
        pause 1             ' using 1 ms delay to avoid latency
        if INTCON.1 then    ' test RB0 interrupt flag
           rb0led=RB0LED ^1 ' toggle RB0LED status
           INTCON.1=0       ' reset interrupt flag
           endif
        next                 
    goto start              ' do it forever

[Mark]

Thanks Steve

This is great - these examples give me 2 ways to use the interrupt.

I will try these out - but before I do I have a question about the first example using the On Interrupt.

I assume we need to disable the interrupt in the handler so we don't get caught in a endless loop - is that correct ?

Should we have the "disable interrupt" inside the RBOinterrupt routine at the start ?

[Mark]

I have tested both examples and they both produce the same function.

They compile into 108 vs. 103 words.

I modified the code and found the answers to my questions - There is no substitue for testing.

I don't have an exact application in mind yet so it is good to know both.

Do you have a preference for one technique or a simple way to describe the trade offs between the two?

Thanks for your help.

[mister_e]

Do you have a preference for one technique or a simple way to describe the trade offs between the two?

Since every project are different, need are also different. I don't prefer one to another, just need to know what i need and how much time i want to spend on. But more than often i'll use ON INTERUPT.