Re: Shared Direction pins vs dedicated Direction pins

Sounds like a single bit sigma-delta DAC with the output being a physical position instead of a voltage like in my CD player.
How high does the bit rate need to be to get a reasonable bandwidth at the motor?

--- In CAD_CAM_EDM_DRO@yahoogroups.com, "Mariss Freimanis <mariss92705@y...>" <mariss92705@y...> wrote:
> 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