Re: [CAD_CAM_EDM_DRO] Re: Black box

Art Fenerty wrote:

> Definitely nice Tom, but the holy grail, I think, is to do it
> without any hardware added to your computer at all.
> It's what keeps me interested anyway.

And, it is totally clear to me that you CAN'T do this, with any
processor
at all, from a DSP, to a 1 GHz Pentium, whatever, your choice!

Actually, I DO know a way to do it, and there might be hardware that is
already on the PC that can be used. What you need is to compose a
huge bit stream, and put 1's in there where you want steps, and 0's
where there should be no step. Then, you send this stream out to
the stepper drive. I can think of the sound port as a device that does
something like this, already. The video data coming out to the video
monitor also does this, but I don't see much of a practical way to
subvert that, without losing your screen display. Possibly the floppy
port could also be used to generate the bit stream.

But, most computers now have an ECP port, and it can do DMA to
the data port. SO, you compose a chunk of the bit stream, and then
just need a timer out on the parallel port to handshake the bytes
out to the data port. When the stream is done, another stream
is already ready to be sent. This should actually work, shouldn't
cause too much overhead if the byte rate is set low enough, and
the stuff added to the parallel port sounds like a one shot and a
gate or two, to be quick and dirty, or a crystal oscillator and
a counter chip if you want to precisely control the rate.

Anyone want to try implementing this? (Or will it be OK to wait a
couple of weeks for my stepper timing chip, which should give
better control with less overhead.)

Jon