Re: [CAD_CAM_EDM_DRO] Re: Parallel Port Interface cards

Phil Mattison wrote:

>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,
>

I don't believe this is true. Maybe it depends on what BIOS mode selection
(AT, PS/2, EPP, etc.) has been made, but when I use any recent mobo parport
in EPP mode, it definitely has active pull-up, ie a transistor, when
driving the
data lines as output.

I have also found that all input control signals have either pull-up or
pull-down
on them. It varies from maker to maker exactly what the value of these
pull-up/
pull-downs is, but they all seem to have this and go to a defined
default state
when nothing is connected.

I sell 3 devices that control motion systems using the parallel port,
all in EPP mode,
and so I have spent DAYS looking at parallel port signals on an
oscilloscope.

Jon