Trigger on rising edge
After Trigger fires:
    RISE_EDGE = CCPR1H:CCPR1L;

LOOP:
    Trigger on falling edge
After Trigger fires:
    FALL_EDGE = CCPR1H:CCPR1L;
    Pulse High Width = FALL_EDGE - RISE_EDGE;

    Trigger on rising edge
After Trigger fires:
    RISE_EDGE = CCPR1H:CCPR1L;
    Pulse Low Width = RISE_EDGE - FALL_EDGE;

    Goto    LOOP

This takes advantage of wrap around on the 16-bit arithmetic.

Bob Ammerman
RAm Systems

----- Original Message -----
From: "Tony Nixon" <tony.nixon@ENG.MONASH.EDU.AU>
To: <PICLIST@MITVMA.MIT.EDU>
Sent: Monday, July 14, 2003 7:18 PM
Subject: [PIC]: Capture Module


> Hi all,
>
> Anyone care to share how they use the capture module to monitor pulse
> streams.
>
> Can it be done??
>
> I may be wrong here, but my idea of a capture module is to
>
> CaptureLoop:
>   Activate capture function
>
>   Hardware takes over...
>   {
>     Trigger on a valid edge
>       = auto reset TMR1
>       = interrupt if required
>
>     Capture on next valid edge
>       = auto store TMR1 as result
>       = auto disable capture
>       = interrupt if required
>   }
>
>   [Capture occurred]
>
>     if TMR1 overflowed
>       Bad pre/post scale factor  // > $FFFF
>
>     Process data
>     goto CaptureLoop
>
>
> The capture module does not appear to work this way as TMR1 is free
> running.
>
> This would(?) give capture scenario as...
>
>   Monitor capture flag, or interrupt
>
>   [Capture occurred]
>   {
>     Did TMR1 overflow?
>
>     No
>       Capture value = TMR1_new - TMR1_old
>       TMR1_old = TMR1_new
>       Process & continue
>
>     Yes
>       Overflowed once
>         if TMR1_new > TMR1_old
>           Bad pre/post scale factor  // > $FFFF
>         else
>           Capture value = $FFFF - TMR1old + TMR1new
>         TMR1_old = TMR1_new
>         Process & continue
>
>       More than once
>         Bad pre/post scale factor    // > $FFFF
>         TMR1_old = TMR1_new
>         Process & continue
>   }
>
>
>
> regards
>
> Tony
>
> --
> http://www.piclist.com#nomail Going offline? Don't AutoReply us!
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>

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