Re: [CAD_CAM_EDM_DRO] Re: Black box again

Jon,

I continue to be impressed. I am going to look for a hard disk drive.

Also, could you tell us a little about this 1284 spec? Could the parallel
port be accessed using basic poke and peek commands using this spec? Is it
not a bios spec? Dumb questions?

Tom Eldredge

----- Original Message -----
From: Jon Elson <elson@...>
To: <CAD_CAM_EDM_DRO@yahoogroups.com>
Sent: Wednesday, June 27, 2001 1:52 AM
Subject: Re: [CAD_CAM_EDM_DRO] Re: Black box again


> Alan Marconett KM6VV wrote:
>
> > >From what I've seen, the problem is more that DOS can't see an LPT at
> > C400h. The port doesn't appear to be there at all, it simply doesn't
> > show up!
> >
>
> Well, DOS sure won't look for it at that address. Many earlier PCs
> didn't even decode more than 10 I/O address bits, so the same I/O
> addresses repeated from 0 to 3FF, then 400 to 7FF, etc.
>
> > So you're doing full 1284 xfers (handshake managed by hardware)?
>
> Umm, sort of. The 1284 spec is both hardware and software protocol.
> We didn't want the heavy protocol overhead, with a CPU in the device
> to identify its make and model, etc. But, the single I/O instruction to
> handshake 1 to 4 bytes of data across the port is a HUGE help in keeping
> the port from becoming the bottleneck. I can do the servo cycle for
> 3 axes in 50 uS on a 333 MHz Pentium II, and I haven't made the best
> use of the 1284 features, yet! (This includes the PID calculation, etc.
> to compute the next velocity to send to the motors.)
>
> So, I just grab the port registers and start throwing bytes at them.
> The real time section of EMC is pretty devoid of driver software,
> anyway. Using single byte transfer cycles, it does a transfer every
> 1.2 - 1.6 uS. Using the multi-byte transfers, it should go a bit faster.
> I will eventually get set up on the logic analyzer again and make new
> measurements.
>
> Jon
>
>
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