Ayaz,
I recommend using a counter output instead of a digital output for PWM generation, as this provides much better performance and resolution while disburden the computer's CPU from an digital output task with high data rates. Please refer to the examples that ship with NI-DAQmx.
Please note, that this type of control doesn't provide an ideal method for velocity control. The PWM duty cycle is proportional to the current that the MOSFET drives through the motor. Current is proportional to torque. If you want to control the velocity precisely, you will need to do closed loop control with a feedback device like a quadrature encoder. This results in the necessity of deterministic software timing, which can't be accomplished under Windows.
There are a lot of threads in this forum about using DAQ devices for motion control tasks. Please refer to this thread as a starting point to learn about the requirements for such a setup and about alternative approaches.
Kind regards,
Jochen Klier
National Instruments
