On 12/29/2013 11:30 AM, Peter C. Wallace wrote: > On Sun, 29 Dec 2013, Josiah Morgan wrote: > >> Date: Sun, 29 Dec 2013 11:07:53 -0600 >> From: Josiah Morgan <josiahmor...@gmail.com> >> Reply-To: "Enhanced Machine Controller (EMC)" >> <emc-users@lists.sourceforge.net> >> To: "Enhanced Machine Controller (EMC)" <emc-users@lists.sourceforge.net> >> Subject: Re: [Emc-users] linuxCNC BBB capeless >> >> Charles, >> Thanks again for the help. >> Reading the manual for the vfd, it looks like the input is a frequency >> pulse train rather than pwm to control spindle speed. Is there a simple >> way to generate a variable frequency pulse to control spindle speed rather >> than using the pulse width modulation? >> Thanks > > If the PRU stepgen is like most of the LinuxCNC stepgens, you should be able > to use a stepgen in velocity mode as a rate generator for the spindle
Yes, the PRU stepgens will run in velocity mode, which is a good way to get a programmable frequency generator. The only caveat is your pulse width will be fixed so the duty cycle will change with frequency. If that is OK with your VFD you're all set. If not, I'll probably have to code up a frequency generator task for the PRU, unless the required frequency is low enough (below 200-300 Hz or so) you can generate it in the 1 KHz servo thread using the HAL software frequency generator. -- Charles Steinkuehler char...@steinkuehler.net
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