The NI 9505 commanded Motor terminal output and actual Motor terminal output differ by a small amount. The following figure shows the commanded signal sent and the offset for both clockwise and counterclockwise motor voltage. Time offsets indicated are typical.

Figure 142. Commanded Sgnal sent and the Offset for Clockwise and Counterclockwise Motor Voltage
where td1 = 750 ns + 170 ns    is the delay between the active edge of the commanded motor signal to the active edge of the actual motor voltage
td2 = 170 ns is the delay between the falling edge of the commanded motor signal to the falling edge of the actual motor voltage
tcmd_motor_on is the time that the Motor terminal of the LabVIEW FPGA I/O node is TRUE; pulse width cannot be between 0 µs and 2 µs
tcmd_motor_off is the time that the Motor terminal of the LabVIEW FPGA I/O node FALSE signal; pulse width cannot be between 0 µs and 2 µs
Note   The PWM Generation — NI 9505 Example VI in the labview\examples\CompactRIO\Module Specific\NI 9505 directory does not account for these signal delays.

Use the following equation to make sure the actual motor voltage matches your desired waveform:

tcmd_motor_on_calc = tdesired_motor_on + 750 ns

Where:

Table 592.
where tcmd_motor_on_calc is an intermediate value used to determine the correct value of tcmd_motor_on
tdesired_motor_on is the pulse width of the signal you require
Once you determine the value of tcmd_motor_on_calc you need to also ensure that your pulse width is above the 2 µs minimum. Use the following table to help determine the value of tcmd_motor_on to use in your LabVIEW FPGA VI.
Note   The minimum pulse width requirement refers to the commanded motor signal and not to the actual motor voltage.
tcmd_motor_on_calc tcmd_motor_on
0 µs 0 µs
0 to 2 µs 2 µs*
2 µs to (T† – 2 µs) tcmd_motor_on_calc
(T – 2 µs) to T T – 2 µs*
Note The NI 9505 module cannot accept a pulse width less than 2 µs (high or low). Doing so will result in unpredictable performance.
Note T is defined as the period of the commanded motor signal.

Use the tcmd_motor_on time to set the Motor terminal of the LabVIEW FPGA I/O node TRUE to compensate for signal delays. Refer to NI 9505 Motor Output and Current Sense Example for a sample motor signal calculation.