Homebrew PCBs

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.

On Sun, 12 Oct 2003 03:11:09 -0000, ghidera2000 <ghidera2000@...> 
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.
>
>
parallel port drives high..
I know some which have connected leds direct to it and it survived..
so it is current limited somehow.

if i remember correct on old mainboards one could see the pullups (&replace 
them)

You need no external pullups..

(This is only MY experience, not any standards or something, just what i 
saw on various ports)

st

--- 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

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