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

> An opto goes not have current gain so you will not get any

buffering

> from using one. If signal levels or drive are an issue, buffering
> on one side or the other (or both) is required. You can get level
> translation, for example where the input is 3.3V like some of the
> new parallel ports. If the source will supply the required current
> then the output can be referenced to any voltage within the specs

of

> the opto transistor. Since optos are current devices and require a
> relative large amount of current with less than unity gain, they
> exhibit a level of noise immunity that a high impedence input does
> not.
>

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.

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 ?

Dave