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I'm having a bit of a problem with the limit switch configuration on a machine that I'm in the procedss of building. Here are the basics:
Controller: UC300ETH-5LPT
BOB: UCSB (connected to Port 2)
Limit Switches Conventional snap action (N.C.)
The wiring is shown on the attached schematic. When I measure the voltage at I10, I get 24 volts. When I trip the limit switch, the voltage drops to zero. The other two axes perform in a similar manner.
Attached are screen shots of the axes configuration.

Questions:
1. Why won't the limit switches interupt the travel when tripped?
2. Why doesn't the I/O monitor reflect the change in status of the limit switches?

I think the only answer for your 2 questions is that the limit switches do not work, they do not trigger the UCSB BOB input or the UC300ETH-5LPT does not receive the signal or the limit input pins are not setup correctly.
I see these as possible reasons.

Is your COM going to the 0V on the board next to the +24V?
And are you sure you are plugged into port 2?

When you activate the switch, you need to see it working on the Diagnostics screen. If you are not seeing the LED change state on the screen, you either have the wrong port/pin, or a wiring issue.

I re-checked the wiring and everything appears to be correct. When I measure the voltage from I10+ to I10- (X-axis) I get 24 volts. When I trip one of the X-axis limit switches the voltage drops to 0.25 volts. I get the same result when I check the other two axes. In the configuration screen I have the limit switches set for active low.

I am using the same limit switch as the home switch.

I still cannot get the limit switches to stop the motion on any of the axes and it does not show up on the diagnostic screen when a limit is tripped!

What am i doing wrong?

What are the correct configuration settings?

You have the same input set as active low and high. You must set all instances of the same pin to the same active level.

My frustration is growing exponentially! This should be the easiest part of the setup and it's turning into a nightmare. For purposes of this explanation, I am going to refer to the X-axis, but all of the axes perform the same way.

The +limit and -limit are wired in series with +24 volts connected on one end; the other end connects to I10+ on the UCSB. I10- is connected to common ground. See my attached schematic.

I have all three functions: LIM+, LIM-, and HOME linked to I10 but the "ACTIVE LOW" box is not checked. Seems to me that it should be. In this conditionthe limit switches do not appear on the diagnostic screen when they are tripped, nor do they have any effect on the X-axis motion.

Now when I check the "ACTIVE LOW" box for all three functions, the diagnostic screen indicates that all three functions, LIM+, LIM-, and HOME, are lit up. (Registering HIGH?) But the controller immediately goes into a "RESET" condition. The message screen prints four lines of the following message: "MACHINE IS IN RESET" follwed by " LIMIT SWITCH TRIPPED".

Can anyone help me figure out what is going on?

I have all three functions: LIM+, LIM-, and HOME linked to I10 but the "ACTIVE LOW" box is not checked. Seems to me that it should be. In this condition the limit switches do not appear on the diagnostic screen when they are tripped, nor do they have any effect on the X-axis motion.

Then you either have something else configured on the same pin #, or it's not wired correctly. There's a pin mapping plugin you can enable that will check if you have a setting conflict. If it's a wiring issue, disconnect everything, and wire one switch. Verify the LED on the diagnostic page changes when you activate the switch. Only when it's working, add another switch and test.

Now when I check the "ACTIVE LOW" box for all three functions, the diagnostic screen indicates that all three functions, LIM+, LIM-, and HOME, are lit up. (Registering HIGH?) But the controller immediately goes into a "RESET" condition. The message screen prints four lines of the following message: "MACHINE IS IN RESET" followed by " LIMIT SWITCH TRIPPED".

It foes into Reset becasue it thinks the switches are active, when you check the Active Low box.

BertZ wrote:the diagnostic screen indicates that all three functions, LIM+, LIM-, and HOME, are lit up. (Registering HIGH?)

The display in the diagnostic screen lights up if UCCNC thinks the pin is active. Since you have them set to Active Low, that means the software believes they are low. That is also why the limit fault trips immediately.

Can anyone help me figure out what is going on?

The UCSB has LED lights for each input. Each LED will be lit if the corresponding input is high, regardless of the Active Low or Active High setting in the UCCNC software. You need to start by looking at the LEDs on the UCSB. Do they light up when the switches are closed? Do they extinguish when you open the switch?

Don't bother looking at the UCCNC diagnostics page until the LEDs on the UCSB are behaving correctly.

I followed the suggestion to disconnect all of the I/O. Then I connected two wires to the normally closed contacts of a limit switch. One of the wires was connected to the positive terminal of a 24 volt power supply. The other wire was connected to the I10+ terminal on the UCSB. The I10- terminal was connected directly to the 24 volt common terminal.

The results were the same. The controller is not recognizing the input signal from the limit switch when it goes from 24 volts to 0.7 volts. The corresponding LED on the UCSB does not light up or go out when the limit switch is triggered.

After exhausting all other possibilities, I considered the one remaining possibility - a defective UCSB breakout board. Fortunately, I had a spare UCSB board that I purchased anticipating more I/O requirements. I switched the spare UCSB with the one that was acting up. My hopes were dashed when the replacement UCSB demonstrated exactly the same behaviour.

So here we are. I have a $4000 piece of junk. Why? Because the bloody controller will not recognize inputs from the limit switches. I appreciate the suggestions I have received so far, but unfortunately no one has come up with a solution to my dilema. Is it time to buy a new controller?

The cable between UCSB and UC300ETH-LPT5, is it connected to port #2 and have the correct orientation? I.e. the red marking on the cable is at the end of the UC300ETH-LPT5 and not close to port #1?
The same for UCSB, the red marking should point to the 24v input.
Do you have a multimeter? Connect one probe to ground, and one at pin 10 on the IDC connector of the UCSB, set instrument to measure Volt, trip the limit switch and check if the voltage changes.