I just wanted to make sure that there wasn't an easier/better way to
measure a pwm signal.

I have obtained some ADXL202E dual axis accellerometers from Analog
Devices, and want to hook one up to my IPaq.  Rather than taking control
of the serial port, I'm going to make a simple interface with a 16f877
(sort of a portable lab toy) and then interface that to the IPaq.

The ADXL202 puts out two signals whose duty cycles vary with the
acceleration the device is under in the two axis'.  Since the period of
he signal is controlled by a resistor (which can vary according to
temperature) then I need to occasionally (every few minutes) find the
total period, and when I need the data I need to find the width of the
pulse.

My understanding is that the easiest way to do all this is:

Measure total period:

Set CCP to capture, positive going pulse
When a change is captured, reset timer one
When the next change is captured, the value captured is the period


Measure Pulse Width:

Set CCP to capture, positive going pulse
When change is captured, reset timer one and set capture to occur on
negative going pulse
When next change is captured the value captured is the pulse width

The duty cycle can be found by dividing the pulse width by the total period.

Assuming that's the best way, then I only have a few questions:

If the two pulse trians (x axis, y axis) start at the same time, then I
won't have a problem measuring both simultaneously with the two ccp
pins.  However, if they are not the same then I'd have to either measure
them seperately, or simply capture the readings for the start and stop
of each event, and use subtraction to determine the length without
reseting timer one.  By doing so, though, I risk timer one overflowing
and having to deal with subtraction across the zero boundary, which
doesn't sound like fun to me.

Is there a better way?  Since my initial experiments are going to be
under 10 Hz sampling, then it's not an issue to measure them at
different time, and it will show me if they are synchronized, so I can
do it this way fine, but I'd still like to find out if there's something
better out there.
-Adam

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