HMI can connect to PC over ethernet directly, but not a switch or PLC

Hello, I am working on a project using an AB Micro850 PLC in combination with a PanelView800 series 2711R-T4T HMI panel. I was previously using a switch to connect both of them to my PC, with the intention of eventually just leaving a single Ethernet connection directly between the two devices.


It was working fine up until some sort of strange failure caused the HMI to no longer be able to connect to either the switch or the PLC directly, even though I am still able to connect to it from the PC using the exact same IP settings as before. Neither the switch nor the PLC's ethernet ports show any activity indication when connected to the HMI, while the HMI's port is slowly flashing both its LED's on and off. I should add that both the PLC and the switch are perfectly functional, I can connect to the PLC over the switch no problem.


Could this be symptomatic of some sort of physical failure in the HMI? The issue persists even after doing a full reset, trying every cable-port combination and loading various different projects or even none at all.

Even though you can connect to the PLC I suspect the switch could be the problem.

If you can try another switch that would isolate a switch problem.

Another thought is the IP address. Maybe something got assigned the same IP as the PV800 and it now has a conflicting connection. Check to see that the IP's for the PLC and PC haven't changed.

Maybe something to do with autonegotiation of MDI/MDIX ?
Is this setup in any of the devices as automatic or fixed to a certain value ?
Today, it is almost universally always automatic. If something is set to fixed, it can be that maybe the switch doesnt handle it - despite that it should.

I doubt the switch is the problem, considering that I cannot connect the panel to the PLC directly either.

As for IP configuration, both devices as well as my ethernet card have static addresses on the same subnet, I haven't changed any settings from the start and have verified it at every step. One thing to note however is that the HMI doesn't seem to indicate any address when it is not connected to some network - but as soon as I plug it in the static address I've set in the "set static IP" screen shows up in the communcations screen.

One thing I cannot of course determine is the PLC's address when it is connected only directly to the HMI, but it doesn't just randomly change under any other circumstances so I think it's unlikely.

Wouldn't the activity indication lights still light up even in cases of address conflict? Because the PLC's are completely dark when connected to the HMI directly.

Is there anything different about the ethernet port on a PC compared to that on a typical switch or PLC that could explain the different behaviour? Apologies if my questions seem dumb.


ETA:

Maybe something to do with autonegotiation of MDI/MDIX ?
Is this setup in any of the devices as automatic or fixed to a certain value ?
Today, it is almost universally always automatic. If something is set to fixed, it can be that maybe the switch doesnt handle it - despite that it should.

Click to expand...

PLC has been set to autonegotiate speed and duplex mode (not the same thing) at every point. I haven't been able to find a comparable setting on the HMI, though I will try to see if that could be the issue.

The status lights only flash when data is being transferred. When on solid (on most switches) it just means connected. If there is an address conflict or incompatible IP/subnet they will still light.

The PLC address does not change when set to static, the only way of changing it is by programming it to a different number.

To connect the HMI directly to the PLC you may need a crossover CAT5 cable, a switch auto determines the need to crossover or not. Also, the switch can connect to different baud rates and duplex. An older SLC505 with only a 10M baud can connect to a PC using 1GIG baud through the switch, but if connected directly the settings must match exactly.

Aabeck said:

The status lights only flash when data is being transferred. When on solid (on most switches) it just means connected. If there is an address conflict or incompatible IP/subnet they will still light.

Click to expand...

Well, in that case the issue must be somewhere in the network layer or below because none of the lights are going up, period. All the lights function normally in the configurations where communication works (PLC-PC, PLC-switch-PC, HMI-PC).

The PLC address does not change when set to static, the only way of changing it is by programming it to a different number.

Click to expand...

Exactly. Which is why I don't think the issue could be IP conflict. I have verified the fact that the addresses are the same as they were before.

To connect the HMI directly to the PLC you may need a crossover CAT5 cable, a switch auto determines the need to crossover or not.

Click to expand...

I was using a regular cable before (and it worked), but I made a crossover cable in the time since making the last post and tested it both for the direct connection and the connection over switch. Same results - no lights for the direct PLC or switch connection, but everything works if I connect the PLC to the switch with said cable. Similarly, I was still able to connect my PC directly to both devices just like before with the crossover cable. As far as I can tell the crossover cable made absolutely no difference in any combination.

Also, the switch can connect to different baud rates and duplex. An older SLC505 with only a 10M baud can connect to a PC using 1GIG baud through the switch, but if connected directly the settings must match exactly.

Click to expand...

I haven't messed with any of the baud/duplex settings. As far as I can tell there is no user accessible way to set these in the HMI anyway. The only things I can do are enable/disable DHCP, set a static address, set a subnet mask, set a gateway and enable/disable the port all together.


This whole issue just seems incredibly odd to me. If this is something that can be caused by either configuring/programming the thing wrong or some environmental factor I would very much like to know how to avoid this failure mode.

You could try a PV reset and return your panel to out-of-box condition.
Be warned you will loose your graphic application, setting, logs, etc.

To do this connect a USB keyboard to the PV and hold the Ctrl and Shift keys simultaneously, while starting up the PV.

When prompted select Yes or F1 to return the PV to factory defaults.

novice_user111 said:

Well, in that case the issue must be somewhere in the network layer or below

Click to expand...

Is the switch only for this PLC - HMI setup, or part of a larger network? I had a waste treatment control go down after a power outage because before all the PLC's came back online the router assigned some IP addresses to other computers on the network it was connected to. That system now has its own, not-connected, network.

Have you tried replacing all of the CAT5 cables - one at a time and testing after each? It might be something as simple as 2 shorted conductors in one cable taking the comm's down.

Have you tried Factory Defaults, and then Flash to your latest FW and re-DL?

I am curious what type of switch you have? I have need ARP tables get filled and not purged, then the switch can not remember which port?

It may also have the HMI MAC at a different IP?

Aabeck said:

Is the switch only for this PLC - HMI setup, or part of a larger network? I had a waste treatment control go down after a power outage because before all the PLC's came back online the router assigned some IP addresses to other computers on the network it was connected to. That system now has its own, not-connected, network.

Have you tried replacing all of the CAT5 cables - one at a time and testing after each? It might be something as simple as 2 shorted conductors in one cable taking the comm's down.

Click to expand...

The device is isolated, only the PLC, HMI, switch and my laptop are ever connected to the network.

I tried swapping the cables, even brought in some I had lying around on the side, no luck.

Have you tried Factory Defaults, and then Flash to your latest FW and re-DL?

Click to expand...

I reset the HMI to what they call "out of the box" condition, but I haven't tried to flash the firmware yet. Will try.

I am curious what type of switch you have?

Click to expand...

havis econ 2040B-A. But in order for any sort of ARP traffic to take place we first need a physical connection with blinking lights, right?

It may also have the HMI MAC at a different IP?

Click to expand...

How would I verify this? The switch is a dumb switch, there is no way for me to see what's going on inside. I could try to procure another one tomorrow. Wouldn't the symptoms of this be a bunch of ARP traffic from unassigned devices that I can see on wireshark?

KuulKuum said:

You could try a PV reset and return your panel to out-of-box condition.
Be warned you will loose your graphic application, setting, logs, etc.

To do this connect a USB keyboard to the PV and hold the Ctrl and Shift keys simultaneously, while starting up the PV.

When prompted select Yes or F1 to return the PV to factory defaults.

Click to expand...

I did this before making the thread. Didn't change anything.

Apologies for self-bump, but I did some more rigorous testing today, using the cables in all configurations and recording the results.
The PC, PLC and switch must be capable of MDI/MDIX autoconfiguration because I didn't run into issues before. I also brought in a spare which is a direct cable, if the coloration of the leads is to be believed.
With the crossover cable, I noticed short, abrupt flashes of green on the switch that coincide with the green-red flashing on the HMI's indications.
With the direct spare cable, I also noticed these except the previously periodic flashing of the HMI's indications was much reduced or gone alltogether.
Strangely, I also noticed that the direct cable I had previously been using to connect the HMI to the switch produced no response when trying to connect the PLC to the switch, even though I was able to use it to connect the PC to the PLC and the HMI directly. This particular cable may have been exposed to moisture yesterday, but the results are very strange and inconsistent nonetheless.
Here are all the configurations with their respective results:
cable 1 (direct, originally HMI-switch)
PC-HMI : Y
PC-switch : N (no activity)
PC - PLC : Y
PLC - HMI : N (flashing on HMI)
PLC - switch : N (no actvity)
HMI - switch : N (flashing on HMI)
cable 2 (crossover, originally PC-switch when it was still a direct cable)
PC-HMI : Y
PC-switch : Y (delay)
PC - PLC : Y
PLC - HMI : N (flashing on HMI)
PLC - switch : Y
HMI - switch : ??? (abrupt flashes of the green LED on the switch, doesn't reach full brightness; HMI flashing regular on the red, arhythmic on green)
cable 3 (direct, originally PLC-switch or PLC-HMI - worked in both configurations)
PC-HMI : Y
PC-Switch : Y
PC-PLC : Y
PLC - HMI : N (flashing on HMI)
PLC - switch : Y
HMI - switch : N (flashing on HMI)
cable 4 (direct, spare)
PC-HMI : Y
PC-switch : Y (delay)
PC-PLC : Y
PLC-HMI : N (flashing on HMI)
PLC-switch : Y
HMI-switch : ??? (abrupt flashes of the green LED on the switch, doesn't reach full brightness, HMI flashing intermittent and reduced in frequency or gone)
Here are the flashing modes:
1. "Normal" flashing on the HMI when failing to connect
https://gfycat.com/ThisEarlyBoa
2. Abrupt green flashes on the switch and altered flashing on the HMI with the crossover cable:
https://gfycat.com/ImpeccableEuphoricHammerheadshark
3. Abrupt green flashes on the switch and no flashing on the HMI with the direct cable:
https://gfycat.com/SomeMadeupGemsbuck


Could this be indicative of some sort of hardware failure? I will try reflashing the firmware next, but if something in the port itself has been damaged that will not be a solution.