Re: [CAD_CAM_EDM_DRO] Windows PC as CNC controller

Holy cow!

Thanks for pointing that 1.2 MHz rate. I had misread it as 120 KHz.

For most PCs (I'd say all, but I don't like absolutes), a 1.2MHz
interrupt rate is not possible. A single OUT or IN instruction for one
of the 3 parallel port registers takes around 1 microsecond, regardless
of the speed of the CPU. If you want to use more than the 8 data bits,
or you want both inputs and outputs, then you need at least two reads or
writes, which will prevent you from going faster than 500 KHz. That is
of course without counting any processing you want to do, and without
counting the very significant context switching time.

I do know of one EMC2 user who got his Athlon 1800 (I think) down to a 6
microsecond period for the step generation thread, or around 160 KHz
interrupts (and 80KHz step rate). That's the fastest I've heard of a PC
generating steps.

As for software to do this for you, there are several packages
available. People have already mentioned Mach and TurboCNC. Mach runs
on Windows whereas TurboCNC is a DOS app (and won't run on Windows 2000
or XP, AFAIK).

There's also EMC2: <http://www.linuxcnc.org> You can download a
liveCD, which you can boot and test with, then install to hard drive if
you like. If you want to mess around with CNC controller software, this
is a good way to go since it's open source.

- Steve

John Dammeyer wrote:

>[snip]
>So would you explain why you feel you need 1.2MHz? There's no way I could
>do that rate with a 40Mhz PIC and I've heard that someone has even developed
>a 3 axis control system with co-ordinated motion using a 20MHz PIC; which
>impresses me to no end.
>
>Regards
>
>John Dammeyer
>