This is a snippet of code out of an ISR which handles pulse-width and
frame-time measurements.  It was written in HiTech C, but was originally in
assembly (yes, I'm converting library routines).

Please note that this permits startup-jitters, but the application does not
care, so I got away with a little cheating.  It is possible with this code
to miss the first pulse on either channel.  After that, it runs fine.

Ignore the excess code fragments - I didn't feel like editing it.

static void interrupt isr (void)
        {
        char    c;
        UINT    ThisEdge,                                       // Time of curre
nt edge being processed
                C1Frame,                                        // Frame width c
hannel 1
                C1LastRise,                                     // Time of last
rising edge on channel 1
                C1Duty,                                         // Channel 1 dut
y period
                C2Frame,                                        // same for chan
nel 2
                C2LastRise,
                C2Duty;

        if (CCP1IF)
                {
                ThisEdge = CCPR1;
                CCP1IF = 0;
                if (C1CaptureRising)
                        {
                        C1CaptureRising = FALSE;
                        C1Frame = ThisEdge - C1LastRise;
                        C1LastRise = ThisEdge;
                        }
                else
                        {
                        C1CaptureRising = TRUE;
                        C1Duty = ThisEdge - C1LastRise;
                        if ((CaptureData)
                        && (!(FrameReady))
                        && (MasterCaptureData))                 // Can we save t
his data?
                                eebuf.snap.Tach = C1Duty;       //      Yes, do
it, else drop on floor
                        }
                }

        if (CCP2IF)
                {
                ThisEdge = CCPR2;
                CCP2IF = 0;
                if (C2CaptureRising)
                        {
                        C2CaptureRising = FALSE;
                        C2Frame = ThisEdge - C2LastRise;
                        C2LastRise = ThisEdge;
                        }
                else
                        {
                        C2CaptureRising = TRUE;
                        C2Duty = ThisEdge - C2LastRise;
                        if ((CaptureData)
                        && (!(FrameReady))
                        && (MasterCaptureData))                 // Can we save t
his data?
                                eebuf.snap.CCP2 = C2Duty;       //      Yes, do
it, else drop on floor
                        }
                }

==================================================================
Andy Kunz - Statistical Research, Inc. - Westfield, New Jersey USA
==================================================================