NI 5411/5431
Digital Filter Considerations

When you use external clocking, high-resolution clocking, or divide-by-n clocking, the actual update rate depends on the state of the digital filter.

For external clocking, if you enabled the digital filter, the actual update rate equals half the frequency of the external clock. In this case, the maximum frequency of the external clock is 40 MHz and the corresponding update rate achieved is 20 MHz. If you disabled the digital filter, the actual update rate equals the frequency of the external clock. In this case, the maximum frequency of the external clock is 40 MHz and the corresponding update rate achieved is also 40 MHz.

For high-resolution clocking, if you enabled the digital filter, the update rate is limited to 20 MHz. NI-FGEN reports an error if you disabled the digital filter specified an update rate greater than 20 MHz while high-resolution clocking is in use. If you disable the digital filter and high-resolution clocking is in use, the maximum update rate allowed is 40 MHz.