Devicenet fault bit

Good morning,

I would like to know what triggers the

Local:3:I.StatusRegister.Fault bit. (on 1756-DNB)

Client has deconnected a devicenet device, and it has made a fault in devicenet network.

I do not know which error number was shown at the time of fault.
Is it only error #81 that triggers the fault bit ?

A disconnected device would normally set the devicefailure bit and show which node(s) is/are missing. So what could have caused the Dnet fault?

Thank you !

(I checked first in Rockwell documentation, but found myself lost on alien ground...)

The Local:3:I.StatusRegister.Fault bit indicates that the DeviceNet network has been intentionally faulted by the user program (or an online user) setting the matching Output bit, Local:3:O.CommandRegister.Fault bit.

The 1756-DNB will also display "NETWORK FAULT" on the dot matrix display.

This feature is uncommonly used; it's a way to intentionally cause slave devices to get no outgoing packets, rather than just getting zero-length "Idle mode" packets.

I don't believe that any actual slave device malfunction, or a Bus-Off condition like a short between CAN_L and CAN_H, will cause that status bit to come on. Those kinds of conditions show in the Status tags in S.ScannerStatus or S.DeviceStatus.

It's difficult to diagnose a DeviceNet problem after it has been reset and cleared; none of the A-B modules keep a log of past faults.

Thanks for your fast -and clear- response !

That leaves me with more doubts, as most of the Dnet modules in our plant are coded with StatusRegister.Fault bits as trigger.. (Wouldn't be the first oddity I've seen there)

Much fun ahead..

Thanks again for your valuable help!

Welcome to the PLCTalk forum community !

I can see how someone might take a first look at the I:StatusRegister.Fault bit and incorrectly conclude that it indicates a general or summary network problem. Its actual function is not very well documented.

The best way to diagnose individual device network failures or interruptions is other parts of the Input and Status tags that are defined for the 1756-DNB.

Input tag I:StatusRegister.DeviceFailure is a summary bit that indicates that one or more devices in the scanlist have failed to communicate.

Status tag DeviceFailureRegister[x] is a SINT[8] array (so 64 bits) where each bit represents a communications failure to the associated node number.

Status tag DeviceStatus[x] is the best way to determine the status of individual devices; the common 72 and 78 diagnostic codes will appear there for X= 0 to 63, the possible node numbers on the network.

The Series C and later 1756-DNBs also have some extended CAN diagnostics objects you can get at.

Years ago I built a DeviceNet fault log FIFO based on the scrolling display of a 1747-SDN, but that's long out of fashion.

KEN, THANK YOU !
This is exactly what I needed !

(I can why you are referred to as The Dnet expert" )