Right. I'm reasonably happy that the PC/Mach3/Parallel Port is working at least in part. Of interest, we know that all the inputs are working and at least the X-DIR output.

With the machine connected, earlier, you suggested (or I've interpreted) that the E-STOP control had no effect on Mach3. Is this still the case? (check all wiring is present to the BOB and that the supplies are on). Remember, the E-Stop is a latching switch - typically you press to actuate and have to twist to release (apologies if this is teaching you to suck eggs). By pressing/releasing the E-Stop before I understood that there was no controlled setting of the E-Stop signal within Mach3, and that the signal was stuck either ON or OFF, depending on the active low/high setting within Mach3?

Also, from previous results presented here, you say that the E-Stop control results in the change in state on pin 11 on the Syil DB25 connector alternating from 0V to 1V. In any logic system from 3.3V upwards, that's all logic '0' level.

From previous results presented here, you say that measuring the E-Stop control INPUT to the breakout board switches between 0V and 12V depending upon the switch position. So the control works.

There's one conclusion from this - the BOB is not behaving as expected. The signal path from the E-STOP input (from the switch) to the corresponding E-STOP output (to the PC) is not operating as expected. We're now down to checking that the power to the BOB is correct (and you've confirmed that the LEDs LED1/LED2 are illuminated - which makes me believe the power is on the board). What remains is any ancillary controls peculiar to this board or that the board is defective. Or I've missed something.

I'm going to have a ponder (aka wife's demanding lunch).