Re: Parallel Port Interface cards

You raise a fairly perplexing issue. Since the PC parallel port uses
open-collector drivers for outputs and does not have built-in pullup
resistors on inputs or outputs, any attaching device really should have
them. Inputs should not be allowed to float, and without a pullup the
outputs will do nothing. A 1K pullup will require 5mA sink capability from
any 5-volt driver, well within the limits of any TTL device. A 10K pullup
will result in very slow rise times (on the order of milliseconds) if used
with an open-collector driver and any significant wire length.

The question of male/female connectors is debatable. I also would have
thought the breakout board side should have a male connector, but research
suggests most breakout boards have female connectors, and my experience
suggests that DB25 male/male cables are easier to find than male/female. My
first breakout board design used a centronics connector same as a printer,
but I actually had people asking for a DB25. I suspect people want the
connector to fit whatever cable they happen to have in their junk box. Maybe
the solution is to always offer compatible cables, but there is not much
value added in being a cable reseller.
--
Phil Mattison
http://www.ohmikron.com/
Motors::Drivers::Controllers::Software

----- Original Message -----
From: John Dammeyer <johnd@...>
To: <CAD_CAM_EDM_DRO@yahoogroups.com>
Sent: Tuesday, January 09, 2007 10:19 PM
Subject: [CAD_CAM_EDM_DRO] Parallel Port Interface cards


> Hi everyone,
>
> I've been evaluating a few parallel port interface cards and I'm finding a
> real disparity between how they all work or how they are wired.
>
> I've run into this issue because I connected the Electronic Lead Screw
> spindle sensor onto PIN 13 of the interface card and did not see the index
> pulse. Turns out this particular card has a 1K pull up resistor on the
line
> that the opto sensor has no hope of pulling down to 0 volts.
>
> Grabbed a different Isolated card and this one expects whatever is driving
> it to sink 12 milliamps. Again, not a chance with the spindle index opto
> sensor.
>
> The other anomaly is the various flavours of DB25 connectors. I've always
> thought that most devices that plug into the parallel port usually have a
> connector that mates with what's on the back of the PC. So since the PC
has
> a female DB25S it only makes sense that the device plugging into it would
> have a male DB25P. All the various dongles that I have for In Circuit
> programming EPROMS or FPGAs, DSP interface modules, Dongles for parallel
> port to CAN bus, even dongles for software security all fit directly onto
> the parallel port connector without an adapter cable in-between. Or in
the
> case of the security keys, often between the port and the printer with a
> Male on one side and Female on the other.
>
> Seems not so though for various parallel port interface cards. Some have
> two female connectors that require a male to male cable and then male to
> whatever on the other end. If you wanted to swap out the interface card
you
> might have to dig out yet another cable.
>
> Perhaps I could get some feedback from others as to what exactly is out
> there. If you've put some sort of CNC system on your lathe, what are you
> using for a spindle speed sensor? Does it go directly into the parallel
port
> or is it powered and provides a strong signal?
>
> Does the parallel interface card you are using create a high signal or a
low
> signal when nothing is plugged in?
>
> Any other comments about interface cards?
>
> Thanks
>
> John Dammeyer
>
>
>
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