It looks like you're trying to measure a pulse width or time between edges.

I like to use the Capture (CCP) for this.

Basic idea:

Set up capture for falling edge trigger.
Loop
        if a falling edge was captured
                clear falling edge captured flag
                process edge
        endif
        if a rising edge was captured
                clear rising edge captured flag
                process edge
        endif
Endloop (forever)

On interrupt:
save all registers
if this was a falling edge (I keep a bit variable to tell me what I'm
looking at)
        if the edge is still down (it's been about 20uS by the time I get here..
.)
                record time of the edge (Timer1)
                set to capture rising edge
                flag that we are capturing rising edge now
                flag that a falling edge was captured
        else
                nothing - ignore this edge as pulse was too short
        endif
else (it was a rising edge)
        if edge is still high
                record time of edge, or Timer1 - stored (falling) edge
                set to capture falling edge
                flag that we are capturing falling edge now
                flag that a rising edge was captured
        else
                nothing
        endif
endif
clear interrupt flag
restore registers
retfie



At 08:52 AM 3/11/97 -0500, you wrote:
>I'm using a 16C74 to do a project where I get the sanitized version of a
>real world signal as the input to RB0 (external interrupt). Because this
>signal can be noisy, I can receive several edges from one event. To filter
>out the extraneous pulses, I decided to disable the external interrupt and
>run timer0 for one cycle at maximum scale (gives me a 32msec window where I
>can ignore edges). In the interrupt handler for timer0, I turn it off, and
>make INTE=1 again. (I'm using timer1 and timer2 for other things already).
>
>Now this setup works ... most of the time. Every once in a while (probably
>15 - 20 seconds), I miss a timer0 interrupt. Which means that I never
>reenable RB0, and miss a bunch of legitimate edges. My data collection
>routine runs every 8 seconds so when it notices that no edges have been
>detected since the last time, it reinitializes and I carry on. However, it
>would be better if this didn't happen at all.
>
>Has anybody else ran into this kind of thing? Any suggestions as to what I
>could try? I could just allow all interrupts and filter them after the
>fact, but I'd rather just not process the interrupt in the first place.
>
>thx
>rick
>
>
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Andy Kunz - Montana Design - 409 S 6th St - Phillipsburg, NJ 08865
          Hardware & Software for Industry & R/C Hobbies
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