1734-ADN DeviceNet Doesn't Recognize on Powerup

[DaveW]

I have a DeviceNet network on a ControlLogix PLC consisting of a 1756-DNB and about 30 nodes of VFD’s and 1734 I/O’s. The problem I’m having is that every time we power down the system and power it back up, one particular node, a 1734-ADN would not come back up. The DeviceNet status LED on the 1734-ADN is off and the 1756-DNB gives an error E78. The only way I can get the 1734-ADN to work again is to pull the DeviceNet plug from the 1756-DNB and plug it back in or do a software reset of this module. Resetting power/DeviceNet at the 1734-ADN does not work. I read the manual and it says something about maybe the dup_MAC_id needing more time to complete. I’ve looked and I can’t seem to find where I can adjust this time. Any idea?

 

[Ken Roach]

Interesting ! I would of course check the cable to the 1734-ADN carefully to see if there might be a reason it can't transmit on the DeviceNet bus.

The network LED being in an OFF state does tell us that the 1734-ADN has tried to join the network but has not successfully seen a response to its Duplicate MAC ID Check packet. It's possible that the 1734-ADN isn't properly receiving enough traffic to determine what the baud rate is, and therefore cannot determine what baud rate to transmit the Duplicate MAC ID Check packet at.

The other possibility that I'm thinking is that there's too much traffic on the network for this 1734-ADN to get a reply to its Duplicate MAC ID Check packet. That might explain why unplugging the scanner (which necessarily makes the network go quiet) lets the 1734-ADN connect.

What node number is this 1734-ADN ? Is it the lowest or highest node on the network ?

Are a lot of your devices let for Change Of State, and is it possible that one or more of them is changing state very often ?

Or the opposite; do you have devices with extremely large Polled I/O connections ?

What is the Interscan Delay configuration on the scanner ? You may need to increase that from the default 10 ms to something higher.

Do you have the ability to determine what the DeviceNet bandwidth utilization is (a Woodhead NetMeter or a DNet traffic analyzer are the best tools for this) ?

 

[DaveW]

Thanks for the reply, Ken.
The bandwidth utilization is around 90% at 125Kb. I’ve also change the baud rate from 125Kb to 250Kb but the problem still persists but I didn’t get a chance to check what the bandwidth utilization is. The interscan delay is set at 18ms. I’ve also changed all COS inhibit timer to 50ms and half of the polled devices are put on background poll rate. The 1734-ADN node is 27 and is the 3rd of 7 panels connected via the thick trunk line.
The largest polled devices (PF70’s) are 4 bytes each way. The 1734-ADN uses COS and 113 bytes input and 81 bytes output. What’s funny is the 1734-ADN COS “heartbeat rate” is shown as “scan rate.” I’m not sure if the two are the same? Also, I’m not able to modify the inhibit time.