Can the spindle be controlled with a PWM signal or analog signal? Which pin do I assign the spindle control to in LinuxCNC?

The Spindle can be controlled with either analog (Like with a DAC card) or PWM. If your spindle speed is controlled by an analog signal, (for example, by a VFD with a 0 to 10 volt signal) and you’re using a DAC card like the m5i20 to output the control signal: First you need to figure the scale of spindle speed to control signal. For this example the spindle top speed of 5000 RPM is equal to 10 volts. 10 volts / 5000 RPM = .002 volts / 1 RPM If you need a spindle enable signal, link your output pin to motion.spindle-on. To link these pins to a parallel port pin put something like the following in your .hal file (net spindle-enable motion.spindle-on => parport.0.pin-14-out), making sure you pick the pin that is connected to your control device.