New to Devicenet

I have two nodes going to a 1769-SDN, all is working until I unplug one of the nodes. I get a 78 code on the scanner which indicates loss of the node. My problem is the other node fails in all its functions until I plug the disconnected node back in. Can someone shed some light on this. Should loss of one node affect affect all others? What should I check first? Thanks

what is the error code u see for the node which is not unplugged ?
are you comissioning new netwrok are it was an established netwrok ?
are your resistros properly connected?

I guess you can call it a new commission since its on the test bench. I have the two nodes drop cables directly tied to the SDN connector with a resistor across the white and blue connector on the SDN. I can read the error code on the SDN but where do you get the error code for each node. Sorry, new at this. If you meant the error code on the SDN, it reads 78 then 7 which is the node I unplugged. No other numbers come up. Thanks

Ok, I could use a little information to help, but this is what happened to me once, maybe this will help. I had a situation with a 1794-SDN that had a baud rate "locked" at the highest rate. When I plugged it in to the network, all of the other nodes dropped out. When I unplugged it, the other nodes came back. The 1747-SDN(scanner) was auto configuring to the higher baud rate when it was connected. It ended up that it was a 1794-SDN bad module that needed to be replaced.

Regardless, I would check the baud rates to start.

You need another resistor on your second node. I am assuming you have daisy chained the wiring?

Also the error code should follow the node number on the SDN, ie it will flash the node number and then the error code. At least that is the way it used to work.

The SDN is at 125 and the devices are "smart baud" and sense and set once they hear another device. Both devices/nodes are the identical.

From your response, I take it that the other nodes should not be affected when one faults, that there is a problem with my setup. I wasn't sure whether Dnet worked that way.

allscott,

yes the error code on the SDN then the node number.

I have both cable ends for each node connected to the connector on the SDN. Two reds to the red, two whites to the white, and so on.
My resistor is across blue and white. Should something be connected in series here. Please answer this one.

I'm going to pull out the dull reading manuals for another go through, been awhile and I have actually put anything together til now on the bench. Thanks

here is a devicenet installation guideline it may provide some useful insight I noticed your 78 error message is contained in this article

jim767 said:

allscott,

yes the error code on the SDN then the node number.

I have both cable ends for each node connected to the connector on the SDN. Two reds to the red, two whites to the white, and so on.
My resistor is across blue and white. Should something be connected in series here. Please answer this one.

I'm going to pull out the dull reading manuals for another go through, been awhile and I have actually put anything together til now on the bench. Thanks

Click to expand...

Yes that's wrong. You want to go from the SDN to the first node and then from there to the second node, and you need a resistor on the sdn and the second node (although the scanner doesn't necesarily have to be at the end). Read the installation guide that was just posted, Dnet is very picky on cabling and power supplies. If you do it by the book it works fine, if not you are in for a nightmare.

I that means I will have to setup some sort of trunk line to tap off. I've read the manual suggested twice but it doesn't really show any wiring diagrams. I looked at a T-tap wiring diagram so I have an idea now how to chain from it. Thanks

Don't panic.

The book you need to read before starting a DeviceNet project is the Media Planning and Installation Guide, publication DNET-UM072.


The network you are describing is a valid one:

Device A ------------ 1769SDN ---------------- Device B

Consider this just a trunkline with "zero length" drops. I have built dozens of networks like this.

The proper placement of terminating resistors is to put one at Device A and one at Device B. Both resistors must be 120 ohms. Connect them between the Blue and White wires.

Depending on the length of cable you could actually put them anywhere within 20 feet of the end, but you're building a test bench for the first time and you should do things right.

You are correct that the removal of one node should not affect the function of the other node. It's possible that the program in the controller is intentionally disabling the second node, or idling the whole network, when the first node is removed. But the network itself should stay stable.

THanks Ken I was looking all over for the same article to post but lost track of where I had saved it

Thanks Ken, Mordrid, Allscott. I have spent some time on the ref manual and also UM004A "DNet modules in L5K control system" user manual. I have found some trunk line and a splitter box and now have it set up with term resistors both ends. Measured 60.5 ohms.

I still have the problem when I disconnect one node, get a 78 error
code on the scanner which is correct and the other node will not function. I checked the scanner status register and all is well.

Ken stated "It's possible that the program in the controller is intentionally disabling the second node, or idling the whole network, when the first node is removed. But the network itself should stay stable."

I tend to think that is the answer. I inhibited the program that uses the unplugged node and the other node now works.

I'm using message instructions in that logic to retrieve data from that node. Do I need to stop disable them in the logic when the node fails.

Thanks for the help!!!