Pin reading update speed. (MC50-10)

[ET]

I've hooked up a rotation sensor to one of the multi-function inputs on an MC50-10, and am having some problems reading it.
The sensor pulses high/low voltage 1000 times per revolution of the wheel, with high voltage guaranteed to be > 2V, and low < 2V.
(Usually it reads around 5V and 1V.)
This wheel rotates with the main driving wheel of the vehicle, and is used to calculate speed.

The problem is, that the MC doesn't seem to read these pulses fast enough, or accurately enough for me to calculate a vehicle speed.
I've got a small electronic speed indicator, which is able to correctly read the speed and number of pulses, so I know the signal is good.

What is the fastest that an MC will read a changing voltage on an input pin?

[Randy]

If you are monitoring the "count" signal with the Multifunction input pin and the pin is not configured as a Quad input.
The max frequency is 10,000 Hz.
The frequency High/Low transition levels are dependent on the voltage range selected and are identified in the 520L0719 document (PLUS+1™ Controller Family Technical Information)
The "count" value will be the number of counts received per loop.
Typically this value is accumulated with an Add component in the application.

I hope this helps.