Re: Shared Direction pins vs dedicated Direction pins

Doug,

I have a circuit worked out that is very simple that shares step and
direction on a single line. If the duty cycle of the step pulse is
less than 50% it's CW, if more than 50% it's CCW.

CW = 100010001000...
CCW = 11101110111...

Mariss

--- In CAD_CAM_EDM_DRO@yahoogroups.com, Doug Fortune <pentam@c...>
wrote:

> 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