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

On Wednesday 07 April 2004 11:48 am, ghidera2000 wrote:

> Spent a day drawing up an optoisolation scheme for the parallel
> port. I know the inputs go between +5V and 0V but, when you set an
> output to low, is it connected to ground or does it go hi-Z?
>
> Silly me, I was thinking in terms of sourcing current from the port
> (OUTput...) and getting fancy with transistors. Just as I finished
> the drawing (As usual!) I realized that its TTL and TTL is much
> better at sinking. If it goes to ground then a couple resistors and
> 1N4148's are all I need to drive the opto-leds.

Having something of the sort in mind for the future, I am not understanding
what it is that you're doing with the diodes here. Can you clarify that
aspect of it for me?