Hello;
You can use two counters to accomplish that task.
The first counter can be used and configured as position measurement. That will make the counter to give back the position of the motor.
The second counter can be used as buffered event counter. You just need to route one of the encoder channels to the counter gate, and since you know the frequency of the source, and at every event of a gate pulse, the internal value of the counter is transfered to the buffer, you can do a quick calculation with the number retrieved and the source signal frequency.
Hope this helps.
Filipe A.
Applications Engineer
National Instruments