I got it sorted out now. Was a bit confused by something I read on
parallel ports. Its desciption made it sound like the port wasn't
good at logic high and was really just limited to grounding or high
resistance. I actually got out my multimeter and fired up the KCam
demo just to see.
Looks like Enable is the only line I have to pull high and thats a
safety issue.
--- In
Homebrew_PCBs@yahoogroups.com, "Dave Mucha" <dave_mucha@y...>
wrote:
> --- In Homebrew_PCBs@yahoogroups.com, "ghidera2000"
> <ghidera2000@y...> wrote:
> > I'm just finishing up the design for an A3977SED based
controller
> > board but I'm a bit confused about the parallel port connections.
> >
> > Can the parallel port drive logic high and low or does it just
go
> > active low (sinking) and high-Z? i.e. Do I need pullups to
generate
> > logic high, or can the parallel port handle this just fine?
> >
> > I plan on pulling Enable high on the board and setting it to
active
> > low in the software. That way if the cable pops out I know the
> > drives will stop.
>
> I'm not following this exactly, but as I understand the step
signals
> are generated in software and pulse the chip. the chip sees a
high
> or low as the pulse changes. you do not have to alter that pulse
> train.
>
> dittor for direction. you just swap one phase and it will run the
> opposite direction. again, no need to alter the pulse. and also
> canned CNC software has that function also.
>
> Check the A3977 specs, I thing the chip needs around 1.5 volts on
the
> step or dir pins to change state. since you do not need 5.0
volts,
> but mroe like 3.5 volts, you do not need the pull up or downs.
>
> Dave