forum.cncdrive.com

In the users manual, pg 34 under kernel frequency, it only mentions UC100. Does changing the kernel frequency affect other UC motion controllers such as ETH400 Ethernet?

Yes.

Yes, all of our motion controllers have adjustable kernel frequency.
The UC100 and UC300 has 25, 50 and 100kHz.
The UC300ETH and UC400ETH has 25, 50, 100, 200 and 400kHz.

The kernel frequency sets the step pulse width, because it limits the width of the pulses as the Time period of a signal = 1/The frequency of the signal.
So, the pulse can't be longer than 1/the kernel frequency.
And with steps the edge of change is when the stepping happens in the stepper/servo drive therefor the active side of the pulse can be only shorter than the Tperiod, it is set to 50% in our controllers.
So, with 100kHz for example the active side of the pulse will be 5 microseconds.

It is adviced to use the lowest possible kernel frequency for the application, e.g. if an application requires only 30kHz max. stepping freq. then select the closest upper value for the kernel freq. which is 50kHz.
It is not adviced then to use higher freq., e.g. 400kHz, because then the pulses are shorter and not all stepper/servo drives can accept that high frequencies.
So, make sure to select a kernel frequency which is lower/equal of what your drives can tolerate and can read properly.

I'm using a Gecko 540 that has a 2 us pulse width spec. According to Maris at Gecko using longer pulse width isn't of any benefit. Setting the kernel to 200kHz will produce a 2.5 us pulse width... is that correct?

Yes, thats correct, if the drive is specified to accept minimum 2usec pulse width then using longer pulses is no benefit, but using shorter pulses is a problem.
And yes, 200kHz kernel freq. is 2.5usec pulse width, so it should be OK with a drive which accepts 2usec pulses.