Are you doing context saving?
You mention in the first line of your isr you clear
the intf. This should not be!

Peter van Hoof

--- Tim ODriscoll <tim@stokepogesway.net> wrote:

> Hi Everyone,
> 
> I'm obviously doing something blatently silly here,
> but for the life of
> me I can't figure it out...
> 
> I've got two 16f628's hooked up as a master/slave
> with rs485 IC's
> between them. I'm trying to send one byte from
> master to slave
> (expanding to 4 bytes when I can send one
> successfully). I've done this
> loads of times before on other projects, so it's
> quite frustrating that
> it doesn't work anymore....
> 
> I'm receiving on portb,0, using a falling edge to
> cause an interrupt.
> The problem seems to be that the slave is
> interrupting one more time
> after it's collected the initial byte, but it
> shouldn't be interrupting
> as portb,0 is back to it's idle state of high.
> 
> I've hooked up my dual-channel scope to portb,0 on
> the slave and an
> extra debug pin which I'm pulsing everytime it
> samples the line. The ISR
> only collects one byte. I've added a few ms of a
> delay at the end of the
> ISR before I retfie. The bit-time is 1ms.
> 
> You can see from the attached trace that the slave
> is jumping to it's
> ISR when portb,0 is still high. It's not constantly
> interrupting, it
> only does it twice for each byte I try to send.
> 
> Here's how I've setup ints on the slave:
> 	bsf	status,rp0		; Bank1
> 	bcf     option_reg,intedg       ; Interrupt on
> falling edge
> 	bcf	status,rp0		; Bank0
> 	clrf	intcon			; Prep intcon
> 	bsf	intcon,INTE		; Int on portb,0
> 	bsf     intcon,GIE              ; Global interupts
> on
> 
> ..and the first line of the ISR:
> 	bcf	intcon,INTF		; Clear the INT flag
> 
> ..and the last line of the ISR:
> 	retfie				; Exit the ISR
> 
> I'm not using any other ints on the slave. I've
> tried clearing the intf
> flag multiple times throughout the ISR, but it's
> still re-interrupting
> as soon as it's done it the first time.
> 
> Am I missing something really obvious, or is there
> something I'm getting
> totally wrong?
> 
> Cheers,
> 
> Tim
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