Re: Shared Direction pins vs dedicated Direction pins

Bernard,

Ditto.

And even though the p-port is disappearing,(but will not "really" be
gone for awhile) the current crop of pc-based cnc controllers is
including support for additional i/o with the use of another p-port,
or support of generic i/o cards, or usb, game port or otherwise...

In other words, it's a solution in search of a problem, IMO.

Ballendo

P.S. But a neat idea!

--- In CAD_CAM_EDM_DRO@yahoogroups.com, "Bernard R
<bwjarandall@c...>" <bwjarandall@c...> wrote:

> --- In CAD_CAM_EDM_DRO@yahoogroups.com, Doug Fortune <pentam@c...>
> wrote:
>
> Doug,
>
> While there is no technical difficulty doing time division

multiplex

> with muliple controllers, I don't really see the need. The current
> limitaion is using a single parallel port as the computer

interface.

> From what little I've seen the G2002 project is well in hand so the
> limited output pins should soon be history.
>
> From the practical side I could see a lot of people having problems
> with the concept and trouble shooting such a system would be a
> nightmare for the average hobbyist with limited technical knowledge
> and virtually no test equipment.
>
> Bernard
>
> > re: dedicated Direction & Step pins need 2*N output lines
> > vs shared Direction & dedicated Step pins need N+1 output lines
> > (N is number of axes), thus saving output pins which are limited
> > in number on a parallel port, and hence often a constraint.
> >
> > Chris L wrote:
> >
> > > >>It would appear to be for some type of "single axis at a time
> positioning"
> >
> > Doug wrote:
> > > >Absolutely not!
> > > >This is a general scheme for lathes, mills, routers and

hexapods

> >
> > > Maybe by a "hand cranker".... but, On a CNC mill or Router ??
> Now I am
> > > lost..... Even on my simple 3 axis router, I assure you I can

and

> do
> > > have more than one motor turning, and in opposite directions at
> any
> > > given time, even for simple 2d profiles.
> >
> >
> > Hi Chris:
> >
> > Yup, lots of motors turning simultaneously at different speeds,
> > accelerations and directions, thats how S&D motor drivers work
> > (as you well know!).
> >
> > Yes, I think you are missing something obvious.... the Step
> > signals to the motor drivers are of the order of 1 uS (1

millionth

> > of a second). Apparent smooth motor motion results from emitting
> > one of these pulses (say 20,000 times/sec or once every 50
> millionths).
> >
> > In other words, you could have many (50 channels in this example)
> > sharing a common direction pin, and neither the motors nor the
> human
> > would be able to detect any measurable difference. However the
> Geckos
> > (much as I like them) have a hold-time constraint on the

Direction

> line
> > which precludes their use in a "shared-direction" scheme.
> >
> > <more written offline to Chris>....
> >
> > Doug Fortune
> > http://www.cncKITS.com