Re: Interface. Gauging interest.

Hmmm, Are you sure?

FWIW, an early method of generating the pulses that the G100 now
spits out(the project was called a G2002 back then)was to SERIALLY
load registers which then counted down, outputting a blip each
iteration. Depending upon what you loaded initially, the blips would
happen faster or slower. Then all six of these SERIALLY loaded
devices would output their state--blip or no blip--in PARALLEL...

The reason you got away with it was/is that the top speed was 20Mhz,
and you divided that into some "normal" step rate, so the jitter
between the worst case and the best case was similarly reduced
giving a spectral purity that was/is pretty durn good.

But the point is, the G2002 WAS a serial to parallel "converter",
and I suspect that the Grex still is...

In any serial device where timing is an issue, Latency is dealt with
by buffering the incoming SERIAL stream, and then releasing it in
PARALLEL chunks, with the timing set by the outboard USB device, NOT
the incoming serial stream (at least not directly, you'd include the
rate info in the serial stream.

With the G2002, this was part of the algorithm, since the rate of
pulse output is known and determined by the same clock that is
creating the pulse stream, the distance becomes time, and vice
versa. so you can simply sum the time/distance to keep track of
position.

So you schlep the bits serially into the Grex, (g2002 used USB, so
does Grex, along with ethernet) and you output them in precisely
timed parallel fashion.

Ballendo

P.S. the reason the USB has overtaken the pport is the same reason
we can now consider a cheap USB black box as being realistic.
Speed.
Parallel is/was a workaround for slow computing. Serial is always
gonna be cheaper(fewer traces on a pcb, less wiring, smaller
connectors, etc.). But until the serial busses got fast enough, the
extra expense of parallel was a good tradeoff for the speed it
offerED over serial.

side note: The original "cube" version of the G2002, which begat the
slab, which begat Grex (need some 2001 space odyssey music here<G>)
used PARALLEL distribution of the incoming data. Mariss saw the
writing on the wall as far as serial busses taking over parallel in
all aspects of computing, and in the slab changed the layout to the
one described originally above.


--- In CAD_CAM_EDM_DRO@yahoogroups.com, "Dave Halliday" <dh@...>
wrote:

>
> Apples and Oranges -- serial and parallel.
>
>With Parallel, the computer presents a number of data lines
>simultaneously to the port. Because of this inherent property, it
>is possible to achieve relatively tight synchronization as
>mentioned in previous posts (Marris's in particular)
>
>USB is by it's basic internal nature, a serial protocol and there
>is no good way to "throw a clown suit" over it and turn it into a
>parallel device. USB is fantastic for schlepping files from one
>device to another but when you require precise timing, forget it.
>
>Look at Marris's G-Rex project to see the next stage of evolution.
>It can use either USB or Ethernet which opens up a lot of other
>possibilities that make my brainpan go Hmmmm...
>A bit pricey but not really given all that it does and what it
>replaces.
>Look at the big picture.
>
> Dave

> > In a message dated 5/15/2006 5:09:00 P.M. Central Daylight

Time,

> > ballendo@... writes:
> >
> > Imagine the SAME scenario, BUT the box says, "plugs into your

USB

> > port"...
> >
> >
> >
> > OK, does anyone offer a converter that plugs into the USB
> > port, but has a
> > "parallel port" LPT-1 type connector for use by us OLD
> > folks? I could use
> > such! But wouldn't that obviously require a "machine-code
> > patch" to produce
> > code that would come through such an adapter as that code
> > would come out of an
> > "old" LPT-1? How? COMPLICATED! Makes me tired just to PONDER!
> > Jan Rowland
> >
>