ControlLogix 1756 DeviceNet and 1756-EN2T trouble

Devices had lost communication, upon checking PLC cabinet Device net was flashing E#78 n#1 thru 16 / 1756-en2t showed "cycle power to unit: assert in task idle clock" pc=0x000 0x00021770.

Looking in RSlink it shows the non-functioning devices with red X through the modules and one relay yellowed out under drop downs for that static ip address, i am unable to log into that static ip address from IE but can communicate with another devicenet (seperate static ip address and all of its devices show up without red X)

After cycling power nothing changed, after removing and reinstalling the 1756-en2t module now Devicenet displays NOtx flashes red mod/net light, ok LED solid green / Ethernet module is now stuck in test with solid red ok LED.

Has the 1756-en2t totally failed? is there something additional I am missing?

Thank your for your help.

Welcome to the PLCTalk forum community ! Too bad your first post is a multi-module pileup on the interstate.

It sounds like you have a system that uses a 1756 chassis with both 1756-EN2T and 1756-DNB modules in it, to provide remote connectivity to DeviceNet networks.

In general, it sounds like something has failed in the 1756-EN2T. A solid red OK LED pretty much fatal damage of some kind.

You can try to insert it into a test chassis all by itself to see if it "wakes up". Certainly you should remove other modules in that chassis to see if they are affecting one another (possible but unlikely).

The DNB sounds like it had disconnected from the network previously, but it's possible that it has also been badly damaged. NoTx generally means there's no replies at all from the network devices.

thank you

thanks for your reply and help, I was thinking the 1756-en2t was the issue, the devicenet was fine until the original issue happened that lost all communication this was when the en2t showed the "cycle power to unit assert in task idle clock" with the solid red led, then the devicenet showed the E78 error this i thought would make sense since it is no longer communicating with the contolLogic blocks. after removing and reseating the en2t and powering the system on and off the notx came up.

The 1756-DNB, like most DeviceNet scanners, stores the "Scanlist" onboard the module in nonvolatile memory. It does not come across with the Configuration assembly from the ControlLogix at connection establishment time, like so many other less-complex devices like Analog modules.

So even if the 1756-EN2T failed completely, that should just make the 1756-DNB go into Idle mode and show a code 80 (I think the DNB also makes it clear that it is Idle).

Code 78 means "no message reply from slave device". It's purely on the DeviceNet side of the module, and it usually shows up when a device has been unplugged from the network.

"NoTX" on the 1756-DNB is the electronic equivalent of coming home and finding your door unlocked and calling out "is anybody here ?" and hearing nothing. It's not as bad as it could be (that's Error 79, bus-off) but it's definitely a sign you've got to look around and see why the things you expect to reply aren't replying.

additional

also you are correct it is a 1756 chasis with the following mdules installed: Logix5562, devicenet, ethernet/ip, prosoft, and relay output. photo attached.

gecco said:

Devices had lost communication, upon checking PLC cabinet Device net was flashing E#78 n#1 thru 16 / 1756-en2t showed "cycle power to unit: assert in task idle clock" pc=0x000 0x00021770.

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Devicenet E78 is a failure to communicate with the address listed. So #1, E78, #2, E78 ... means that there is a configuration for each of the addresses but there is no response from the equipment at those addresses. I use the scanner at #1, so I've never seen #1 E78.

If you turn off and lock out a VFD, that one will show up on the scanner as #nn, E78 depending on what address it is.

So your power supply is working (otherwise it would complain about no power) but your devicenet appears to be disconnected somewhere.

How many devices are on your devicenet? Since it lists E78 it must be communicating to at least one other address right now.

Looking in RSlink it shows the non-functioning devices with red X through the modules and one relay yellowed out under drop downs for that static ip address, i am unable to log into that static ip address from IE but can communicate with another devicenet (seperate static ip address and all of its devices show up without red X)

Click to expand...

The Ethernet card will affect the devicenet scanner if your PLC is communicating to the rack and the devicenet card through ethernet. But the ethernet card should not affect what the devicenet scanner shows ie E78.

So it sounds like your ethernet switch is OK.

After cycling power nothing changed, after removing and reinstalling the 1756-en2t module now Devicenet displays NOtx flashes red mod/net light, ok LED solid green / Ethernet module is now stuck in test with solid red ok LED.

Click to expand...

The devicenet scanner is complaining that it can't find anything on the devicenet network to talk to. Notx is sort of like "I'm polling but no one responds". Again, your power supply is still fine. But the Devicenet itself has some issues.

Did you lose one or both of your terminating resistors? - there should be one on each end of the devicenet. You can check for power on the connectors - Red and Black wires should be 24V between. Terminating resistors are across White and Blue wires.

As for the ethernet card - removing it and putting it back in should not have damaged it. It will sometimes show in TEST when it is not seated in the rack properly - or all the way in. Try pulling it out and re-seating it again. It should still have it's configuration. If it powers up without it's IP address you may need to download the configuration to it again.

If the ethernet card stays in TEST with a RED LED - yup - it's broken. Change it out. But I don't believe that was your original problem with the devicenet scanner. I think you have a couple of problems ganging up on you!

Has the 1756-en2t totally failed? is there something additional I am missing?

Thank your for your help.

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Let us know what you see next. This is the sort of headache that it may take a few sets of eyes to figure out.

thank you

I have found an output (#23) that connects off the relay output module then connects to a second plc relay output module (again slot 23) that then goes to an omron relay, this port does not have 25vdc and all the others that are wired do, also the relay is not lit, i replace with a good know relay still nothing, when i move this from #23 to 21 (25vdc) the devicenet then changes to no network? pic of 2 and the omron relays attached. thank you again.

reseated again and still the same issue "test and red light"

gecco said:

also you are correct it is a 1756 chasis with the following mdules installed: Logix5562, devicenet, ethernet/ip, prosoft, and relay output. photo attached.

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So the Logix PLC is in the same rack. OK.

I don't think the ethernet card has anything at all to do with the Devicenet issue.

gecco said:

I have found an output (#23) that connects off the relay output module then connects to a second plc relay output module (again slot 23) that then goes to an omron relay, this port does not have 25vdc and all the others that are wired do, also the relay is not lit, i replace with a good know relay still nothing, when i move this from #23 to 21 (25vdc) the devicenet then changes to no network? pic of 2 and the omron relays attached. thank you again.

Click to expand...

So your have 24VDC (but it measures 25 VDC) to a relay output #23. And that feeds another output (is slot 23 correct?) which feeds an omron relay. And the Omron relay is not energized.

Moving from output 23 to output 21 turns something off (I guess that your PLC program does not have output 21 turned on) and now the devicenet changes to no network.

I would guess that the output is supplying 24V power to some of your devicenet network. It seems a bit strange. Can you check for 24V on any of your devicenet equipment?

You're going to have to trace out the wiring for those relays and examine the PLC program for the output module that controls them.

I see a few unlabeled wires and the placement of the red/blue/white/black terminal block assembly suggests that the DeviceNet might be powered (or even disconnected via the CAN+/CAN- wires !) by those relays.

Follow the CAN+ (usually white) and CAN- (usually blue) signal wires from the 1756-DNB and see where they go. Look for a 120 ohm termination resistor wired across them in this cabinet.

follow up

now after going back and checking the 1756-en2t now shows failed, their is 24v coming out of the devicenet, tested resistor and it is good, there is only one resistor on each of the two devicenet modules none at the other end, these are then connected to relay blocks. I have attached the latest pictures along with the screen shot from the server. thanks for all your help.

additional pics

attached are additional photos of the wiring from the deviceNET that shows no tx to the relay block.

Do you have the electrical drawing?

Are wire labels illegal in DC ?



I'm not sure what's going on here. Probably the first step is to replace the 1756-EN2T so you can get connected to the controller again.

Then find or make some wiring diagrams and swear at the original installers for a while.