Issues with simple input on 7i76eu

Hi,

I am trying to convert my DMC2 Mini from the chinese Mach3 board it came with, to LinuxCNC via a Mesa 7i76eu. And I have most of it working by now But I am having an issue with two simple inputs.

I have two probes, a hight pug and a xy probe, that basically just connects to GND when triggered. They are connected to the mesa with a 10kOhm pull up resistor. This is what I am seeing when I power the machine on:
- The input pin on the Mesa card reads 12v and the input is as expected high/true in hal show
- I then trigger the probe and the input pin now reads 0v, and the input is low/false in hal show
- After I "release" the probe the input pin returns to 12v, BUT the input remains low/false in hal show

Any ideas why the input in hal doesnt return to high when the pin reads 12v with a multimeter
Field power is 24v, and all voltage readings are done between field GND and the input pin.

Thanks in advance

Wait until  someone else confirms but I think your issue is that the  Mach3 board senses on the negative side and the 7i76e senses on the positive side. In other words on the 7i76e, you need to switch the input to +24 volts not GND

Read page 24 of the Mesa manual.

I am pretty sure that you are correct, at least in the part about the inputs being reversed between the two boards.
But it is my understanding that this is why the pull-up resistor is needed, so that the input at idle is 12v and then when activated goes to 0. So to get the correct logic in linuxcnc I use the xxx-not input signal.

But I don't understand why the hal state doesn't change after the first trigger, even though I can see the voltage change on the input pin.

The 7I76EU inputs have a threshold of 60% of VFIELD when going positive and 40% of VFIELD when going negative.
This means with 24V VFIELD, a voltage below 9.6V is read as low and a voltage above 14.4V is read as high.
This  is called hysteresis, and is deliberate behaviour for noise immunity. With a 10 K pullup you end up just in the middle
of this input threshold range, You need a stiffer pullup resistor (say 2.2K) so that you have a valid input to the 7I76EU.

Aahh shoot! I was hoping to avoid resoldering my DIY pullup resistor board. But thank you for the explanation.