The new circuit just as a buffer not as an inverter, so when a low signal input from I/O pin then the stepper driver will be activated, the active signal of stepper drive is from high to low, so the stand by voltage level is high, how do you setup the input signal from I/O pin that it will affects the input of stepper driver.

As your present circuit, after the system reset then the input of stepper driver will be pull high to waiting for a low level to active, and if you want to keep the led of photocoupler at a high level then what will be happens of stepper driver when the I/O pin is at the low level?

To be honest, this thing about the input of the optocoupler still gets my wires crossed. What do you mean exactly? Tech support from the 5i22 card told me:

"Active low is required for reliable operation and to guarantee outputs are off at startup from a hardware standpoint. As far as logic is concerned that's at a higher level and can be addressed by inverting the logic at the FPGA IO pins (if you use our hostmot2 firmware there is a register for this inversion)"

But it still confuses me. As final point, are you suggesting the input configuration that you posted in your circuit above in post #24?

 

To be honest, this thing about the input of the optocoupler still gets my wires crossed. What do you mean exactly? Tech support from the 5i22 card told me:

"Active low is required for reliable operation and to guarantee outputs are off at startup from a hardware standpoint. As far as logic is concerned that's at a higher level and can be addressed by inverting the logic at the FPGA IO pins (if you use our hostmot2 firmware there is a register for this inversion)"

But it still confuses me. As final point, are you suggesting the input configuration that you posted in your circuit above in post #24?

Yes, that's what I will do, you can try both to find out which one is the best for you.

 

What would be wrong with just this?

It does not look like you need really high speed.