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PICList Thread
'Interrupts'
1995\02\08@033839 by Ran Talbott

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You wrote:

>Say I have two interrupt routines.

It's probably better to say that you don't:  one of the tricks I use to save a f
ew
cycles is to do all the interrupt handling "inline",  and check all the possible
interrupt sources on each interrupt.  E.g.:

   Test INTF,  and branch if off
        Handle external interrupt
   Test T0IF,  and branch if off
        Handle TMMR0 overflow
   etc...
   RETFIE

I'd only do CALLs if I had a service routine complicated enough to take up
more page 0 space than I could spare,  or I had lots of spare CPU time,  and
wanted to trade some for a small improvement in readability.  But the
generous use of whitespace in the inline code does almost as well.

>On the RETURN at the end of the RTCC routine, control passes to the service
>routine.  But what if the RB0 flag was checked before the RTCC routine was
>called?  On RETFIE, would the interrupt service routine be called again
>by the uC because a flag was still high??

Yup:  some chips reset their "interrupt pending" status if you peek at it,  but
the PIC requires that you reset it explicitly.  "Just checking" really means
"just checking" in this case:  you have to BCF INTCON,INTF to make it
shut up.  If you don't clear it,  you'll get an unpleasant surprise...

Ran


'interrupts'
1998\02\09@132130 by TORRENS SR
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At present I'm working on a project using the PIC 16c74 and am having a few
problems trying to get the interrupt
working (RB0/INT). Can anyone help ?

1998\02\09@140927 by Najemy, Daniel

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Can you be a little more specific about the problem you're having?

Daniel Najemy -  Data General Corporation, Numaliine Power Systems

> -----Original Message-----
> From: TORRENS SR [SMTP:spam_OUTr139aTakeThisOuTspamSMSERVER2.ULST.AC.UK]
> Sent: Monday, February 09, 1998 1:21 PM
> To:   .....PICLISTKILLspamspam@spam@MITVMA.MIT.EDU
> Subject:      interrupts
>
> At present I'm working on a project using the PIC 16c74 and am having
> a few
>  problems trying to get the interrupt
> working (RB0/INT). Can anyone help ?

1998\02\10@070612 by Diego Sorrentino

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> -----Mensaje original-----
> De:   TORRENS SR [SMTP:r139aspamKILLspamSMSERVER2.ULST.AC.UK]
> Enviado el:   lunes 9 de febrero de 1998 15:21
> Para: .....PICLISTKILLspamspam.....MITVMA.MIT.EDU
> Asunto:       interrupts
>
> At present I'm working on a project using the PIC 16c74 and am having
> a few
>  problems trying to get the interrupt
> working (RB0/INT). Can anyone help ?
>
       Re: Have you set the INTCON register for selecting the interrupt
sources?

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