which way best to use optocoupler?

I want to isolate my parallel port from my step motor driver by optocoupler.
the input stage on my step motor driver is 74HC14N chip.
which one is best ? (the optocoupler on circuit is a sample,not the one my going to use)
and I hope you can give me some explaination about it. thanks

None of them would provide you galvanic isolation !! Ground or Vcc are common in all of them. You need to separate grounds and supply.

thanks CMOS for your help.

lets assume I separate the VCC & Ground.
At the input stage of optocoupler I use 5v & Gnd from USB port then at the the ouput stage of optocoupler I use external voltage source such from 7805 chip and also ext Gnd.

now, which circuit is best (the data pulse frequency from parallel port is around 10khz)?

First, you MUST use, separate power suplies to have isolation in either side of an optocoupler.

Then you calculate the resistor to use in series to drive the optocouplers led.

R = (Vin-Vf)/If

Vin is the voltage you use for input, Vf is the optocouplers led forward voltage drop (you will find it in o/c datasheet) and If is the o/c led drive current (also in the datasheet)
From the circuits you provide, the left will work for you (first separate grounds) if you will drive the o/c direct. In the middle, you add a pull-up of 2K2 in the led anode, I don't find it a good idea because a costant curent will flow trough it. In the right circuit you control the led cathode. This is usefull if you use a transistor as a low side switch to drive the o/c. And the 10K resitor you add between anode and cathode it will make no difference. If you want a logic level from the o/c collector, probably use a pull-up between 1K and 10K.

Also if you want to drive the optocoupler direct from Parallel, i think if you want more than 5mA for the o/c led, you must use a transistor for this (for example a bc547) and a separate power supply.

and take a look here
https://www.epanorama.net/circuits/parallel_output.html

Good luck!

THANKS alot for your infos t_maggot, your explaination really help me.