Hi Dave

if I have read this correctly

Click image for larger version.  Name: step1 stepper driver step & dir inputs.jpg  Views: 688  Size: 191.9 KB  ID: 21891

it looks like for up to 4 drivers
you can have separate step & direction signals to each driver

for more axis they must multiplex the direction signals on pin 7
and store it the appropriate driver board until you need to change that axis direction

I would need to see the detailed data sheet for a stepper 1 driver board or
study a board to trace the direction signal path

I would expect the rest of the circuit to follow the data sheet for the stepper driver IC's used

John