On Interrupt

[Mark]

I am beginning to experiment with interrupts and can see there are many possibilities.

Using the PBP On Interrupt seems easy but I have a few questions about how it works that I can't seem to find answers to in the manual.

1. Does it scan all the interrupt flag bits or just RB0 ?

2. Do enable or disable reset the flag automatically ?

The datasheet states that the flag bit needs to be reset in software so I assume that PBP is taking care of this - I'm just not sure how it does it.

[mister_e]

Just a brief on it!

Before using On INTERRUPT, you must enable the interrupt you want to monitor, RB0, USART, TIMER overflow.... by setting the according registers (INTCON...)

PBP will not automaticaly set it for you, same for reseting the flag intterupt.

Tell us wich PIC you have and wich interrupt you want to monitor and we can do a code snip for you.

[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.