hey guys,

I'm trying to create a totally isolated parallel port drive interface circuit for a particular machine.

I want to use optocouplers for both inputs, and outputs. Outputs are fine, low power optos run directly off the data lines. The problem i run into is the inputs to the PC.

So, i have 2 questions:

1. I notice that several of the input pins are labeled "inverted" and some are regular. Do i have to drive them high, or low or some mixture of each?

2. How can i get power to drive the inputs to the PC high, while remaining totally isolated, without using an external battery? I was thinking using an isolated DC-DC converter 5V in, 5V out, and connected to the machine 5V logic line. Would that give me the isolation i'm looking for? any other way to do it? DC-DC converters are kind of pricey, kind of large, and i'm not swift enough to design my own.