Which vfd is best for linux cnc?

So do I have to buy a separate 5i25 FPGA card or the parallel port on my pc would be enough for using a 7i78 daughter card ?

(I only need 2 axes, so choosing 7i78 over a 7i76)

The vfd i was looking to buy also features a digital input. Perhaps this is standard PWM?

Yes, to use a 7i76 or 7i78, you have to have a Mesa FPGA card such as a 5i25. They will not work with an ordinary parallel port.

I don't know anything about the VFD you are looking at.

alright, i was thinking of just using a DAC to convert the pwm signal to analog 0-10v dc. gonna try that and see if it works this way..

you happen to know the max frequency of the linuxcnc pwm output?

The max frequency from a software PWM generator (parallel port) is going to depend on the computer and how fast it can run a stable basethread, and how good of a resolution you need. According to the docs "depending on CPU speed, etc, is capable of PWM frequencies from a few hundred Hertz at pretty good resolution, to perhaps 10KHz with limited resolution." (I think the 10KHz is rather over optimistic.) Basically the resolution will be the frequency period divided by the basethread period.

Hardware generated PWMs are a lot better, higher frequencies and a lot better resolution.