Re: [CAD_CAM_EDM_DRO] Re: ParPort output low - hi-Z or ground? opto to parallel

On Thursday 08 April 2004 01:20 pm, turbulatordude wrote:

> I am looking at an external power supply thru a resostor on the
> isolated side of the opto. I can drive the LED with 10-15mA and
> attain isolation from the opto as the power supply and resistors and
> LED side of the optos would be on a totally seperate circuit.
>
> On the parallel port side, It would appear that a non-buffered
> connection would have the port pins (10-13) connected to the opto and
> the other side to ground.

This being the _output_ side of the opto, right?

> A state change of the inputs would result in a state change of the
> outputs.
>
> Would a pull-up or pull-down on the parallel port side offer any
> benifits ? and which would be best for the parallel port side of
> things ?

If you have the output of the opto connected between the port pin and ground,
then when it's off that pin is basically looking at an open circuit
connection. It would probably be of some benefit to have a pullup resistor
in this case to provide better noise immunity, and to make sure that the pin
_is_ going to go up when the opto isn't pulling it down.