--- 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