ControlLogix 1756 DeviceNet and 1756-EN2T trouble

yes my sentiments exactly concerning the installation/ wiring... system is 15 years old and pre-dates me, original install was completed national company is sad enough but worst part is it would have been accepted by a project manager.

and of course no drawings exist, submittals show major parts and placement but no wiring or connectivity.

1756-en2t arriving ups today, will post update on install.

Thank you again for your time and help..

I've told customers with systems like that "I'm going to give the patient an autopsy first, then put on a band-aid".

Are you familiar with reconfiguring the 1756-EN2T ? The USB port is probably the easiest way to set it up; RSLinx Classic will auto-create a driver, and you can "drill down" to right-click and set the IP address / subnet mask/ default gateway.

You could also use the traditional BOOTP/DHCP server, or do the same "drill down" via that 1756-L6x CPU's serial port.

Got the new one configured through boot/dhcp is showing 100/full duplex with auto detect checked, now have an issue with the second device net saying no tx? Could there be a conflict? Populated all the info in the new 1756-en2t as the old. Thanks.

Your comment about the "second DeviceNet" caused me to go back through your pictures and realize there are two 7-slot chassis in this cabinet, each with a CPU, DNB, EN2T, Prosoft, and Relay Output module.

I'll bet that this is an improvised redundancy system.

Both 1756-DNB modules are probably intended to connect to the same DeviceNet network, but only one at a time, switched through those relays.

This is NOT the way ControlLogix redundancy is supposed to work. ControlLogix Reundancy systems are very different, with ControlNet or EtherNet/IP networking and Redundancy Manager modules.

If the relays make it so that only one of the 1756-DNB modules is connected to the DeviceNet at time, it makes sense that the other one will always complain about inability to connect to the slave devices (E78 for each slave) or even show NoTx.

So the current problem with your system was probably just the 1756-EN2T module hardware failure.

NoTx versus E78

A simplified note about the different conditions you're seeing on the 1756-DNB scrolling displays.

"NoTX" appears when the 1756-DNB has powered up and gone through its initialization procedure on the network, but it never received any replies. That's consistent with it not being connected to the network trunkline, but still being connected to wire with a terminating resistor.

"E78 N##" appears when the 1756-DNB successfully created and ran an I/O connection, but the slave device subsequently stopped responding to I/O polls and also does not reply to re-connection requests.

These two different messages are consistent with an improvised DeviceNet hot backup system, where only one 1756-DNB is connected at a time. Whichever one is not connected via those relays when it's power cycled is the one that will show NoTX, while the other one will show E78 for every node only if the "hot backup" system fails over and it loses its I/O connections.

Well spotted Ken

Yeah, when first looked at the relay photo there a minute ago I also spotted the DeviceNet bus wiring on the Omron relays wired to both sides of the change-over contacts and thought sweet Jebus! But I didn't dream of it being an attempted "redundancy" setup until I read your comments Ken! There are some really exceptional artists out there in this business and that is a masterpiece, albeit a "forgery".

However, I think there's only one thing that should be made "redundant" here, and that is the installer.

G.