Several people have pointed this out - thank you all. It was meant to check
to make sure that GIE was clear before entering the rest of the routine, but
I mixed up BTFSC and BTFSS. When fixed, it worked fine.

I am not concerned about losing data in the foreground when interrupted. I
am just looping and getting interrupted out of the loop. I realize that I
will have to make copies of the registers when more processing is added to
the loop. I have been reading Myke Predko's book (Programming and
Customizing the PICmicro, 2nd Ed), and he explains the way to do this. I
haven't used interrupts before, so the interrupt coding is new to me.

Thanks,
Andy Meng N8MX

----- Original Message -----
From: Olin Lathrop <olin_piclist@EMBEDINC.COM>
To: <PICLIST@MITVMA.MIT.EDU>
Sent: Sunday, August 12, 2001 9:46 AM
Subject: Re: [PIC]: USART receive problems


> > Interrupt:
> >     bcf           INTCON,GIE
> >     btfss        INTCON,GIE
> >     goto        $ - 2
>
> Interrupts are already off by the time you get into the interrupt routine.
> Nothing will magically re-enable them.
>
> >     bsf          PORTB,LED    ; turn on LED
> >     call         Delay15ms
> >     call         Delay15ms
> >     call         Delay15ms
> >     call         Delay15ms
> >     bcf         PORTB,LED
> >     btfsc      PIR1,RCIF       ; see if RX flag is set
> >     call        RS232_Receive  ; if it is, call RS232_Receive
> >     retfie
>
> Read the section about interrupts carefully.  You have major
misconceptions
> here.  For example, this interrupt routine will randomly and
asynchronously
> appear to trash state in the foreground routine.  After reading and
> understanding the manual, see QQQ_INTR.ASPIC at
http://www.embedinc.com/pic
> as an example interrupt module.
>
>
> ********************************************************************
> Olin Lathrop, embedded systems consultant in Littleton Massachusetts
> (978) 742-9014, olin@embedinc.com, http://www.embedinc.com
>
> --
> http://www.piclist.com hint: The PICList is archived three different
> ways.  See http://www.piclist.com/#archives for details.
>


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