Hi

I'm not sure about the PIC - R23 is adjusting Vref (driven by Q2/IC5A) into it's GP4 input (which for the '675 is analogue input 3).

But it also does take the CLOCK signal that goes into IC3 (L297).

I don't think it's doing anything to Vref, so it must have the capability of driving CLOCK instead. Otherwise, there's not a lot the PIC could do - all the other IO pins are grounded. Do you have the code for the PIC? That would give more of a clue as to what it's doing.

Any particular reason why in yours you aren't using optoisolators?

D11 on yours should be a triac instead (T1 on the original, middle-bottom).

C15 on yours is the reverse polarity (+ve is going to GND) - next to T1 on the original (C27).

I see you've omitted the power supply circuit (top-right) - are you going to power it from the CNTL port (JP3)? I can't see any other method of providing +5V...

Apart from that, it looks good - but I'll have another look later on.

Edited to add: I suppose the PIC could do things with Vref - although the only things it could do are:

- Power GP4 high
- Power GP4 low
- Pulse GP4
- Leave GP4 open

It might power down the stepper controller if the clock hasn't been used for a while. GP2 is also the INT(errupt) input on the PIC. In which case, I suppose a resettable monostable could do the same job.