Re: Shared Direction pins vs dedicated Direction pins

--- 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