SLC 5/05 Ethernet Connections

OkiePC

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I know how connections are created, but how are they released?

Problem SLC: 1741-L551B OS 501, FRN 8
Ethernet Daughterboard Series 2, FRN 59

I don't know if this is a factor, but yesterday there was some maintenace done on a UPS system that supplies power to many PCs, switches and even some PLCs on our controls LAN. They yanked power on a bunch of stuff at various times.

Today, I needed to make some changes to some messaging between two of the SLC 5/05s. I edited (online) a message read from one SLC to the problem SLC. I moved the target (problem) PLC addresses and changed the message length from 2 to 10, and kept the same control block.

After I finished the edits, I noticed that some other messages in the Problem SLC were erroring out. The error message was something like 'already at maximum connections', so I opened the CH1 diagnostics and found that there were 16 connections in use...that can't be right...

So, I did some online editing to temporarily halt all of the messages (four) between the two PLCs by deleting the rungs and then testing the edits. This did not make any difference...even after waiting for about 30 minutes...I still don't know what tells the SLC to begin releasing connections...There is still another SLC that I could not get to which was also still reading from it, but that should only be one connection.

So, I put the SLC in program mode and back to remote run using RSLogix...no difference. Then I uploaded and saved the program, went offline, and then went to the channel connections tab and pushed the clear button to zero out all the counts. I then downloaded the program and put it back in run mode. The connections jumped right back to 16.

Finally, to clear this up, I went to the SLC and cycled power. Now we are back to the normal 6-7 connections. Apparently the ethernet daughtercard holds onto connections even when the SLC is in program mode...which makes sense, cause it still needs to be able to talk to other stuff...

So, this is more informational for others, but I am still curious about the mechanism that would allow those extra connections to be created and then released. I am not 100% sure the editing of the message instructions had anything to do with it, since I did not look for any errors before I started making those edits, and the edits were done in the other PLC, and continued to work even while the connections were maxed out.

Thanks for any insight about how these mysterious connections actually work.

Paul
 
Last edited:
Good question

I know how connections are created, but how are they released?

Problem SLC: 1741-L551B OS 501, FRN 8
Ethernet Daughterboard Series 2, FRN 59

I don't know if this is a factor, but yesterday there was some maintenace done on a UPS system that supplies power to many PCs, switches and even some PLCs on our controls LAN. They yanked power on a bunch of stuff at various times.

Today, I needed to make some changes to some messaging between two of the SLC 5/05s. I edited (online) a message read from one SLC to the problem SLC. I moved the target (problem) PLC addresses and changed the message length from 2 to 10, and kept the same control block.

After I finished the edits, I noticed that some other messages in the Problem SLC were erroring out. The error message was something like 'already at maximum connections', so I opened the CH1 diagnostics and found that there were 16 connections in use...that can't be right...
This has often been a problem for us especially when people are starting and stopping the PLC and every time they start they open new connections without closing the old ones. Eventually our controller would also have a similar error saying all the connections are used.

We have a log that keeps track of the connections being opened and closed and it indicated that the connections were not being closed.
Our solution was to close the connection that has gone the longest without activity. We are assuming that the old inactive connections are closed on the other end.

So, I did some online editing to temporarily halt all of the messages (four) between the two PLCs by deleting the rungs and then testing the edits. This did not make any difference...even after waiting for about 30 minutes...I still don't know what tells the SLC to begin releasing connections...There is still another SLC that I could not get to which was also still reading from it, but that should only be one connection.
I don't think some Ethernet controllers release connections and if you simply turn off the Ethernet controller it has no way of closing the connection so it remains open on the other end.

So, I put the SLC in program mode and back to remote run using RSLogix...no difference. Then I uploaded and saved the program, went offline, and then went to the channel connections tab and pushed the clear button to zero out all the counts. I then downloaded the program and put it back in run mode. The connections jumped right back to 16.
You didn't mention powering off. I have found that works.

Finally, to clear this up, I went to the SLC and cycled power. Now we are back to the normal 6-7 connections. Apparently the ethernet daughtercard holds onto connections even when the SLC is in program mode...which makes sense, cause it still needs to be able to talk to other stuff...
OK. Yes.

So, this is more informational for others, but I am still curious about the mechanism that would allow those extra connections to be created and then released. I am not 100% sure the editing of the message instructions had anything to do with it, since I did not look for any errors before I started making those edits, and the edits were done in the other PLC, and continued to work even while the connections were maxed out.
I wouldn't call them extra connections. I would call them duplicate connections.

The problem is how does one node know that another node is reset or off or simply not active?
 
Not sure if this will be of any help.......

http://literature.rockwellautomation.com/idc/groups/literature/documents/qs/1747-qs001_-en-p.pdf
Page 19

MSG
Connection
Timeout
The amount of time (in ms) allowed for a MSG instruction to establish a connection with the
destination node. The MSG Connection Timeout has 250 ms resolution and a range from 250 to
65,500.
15,000 ms read/write (Default)

MSG Reply
Timeout
The amount of time (in ms) that the SLC 5/05 waits for a reply to a command it initiated via a
MSG instruction. The MSG Reply Timeout has 250 ms resolution and a range from 250 to
65,500.
3,000 ms read/write (Default)

Inactivity
Timeout
The amount of time (in minutes) that a MSG connection may remain inactive before it is
terminated. The Inactivity Timeout has a 1 minute resolution and a range from 1 to 65,500
minutes.
30 minutes read/write(Default)

Page 32
The user may change a MSG instruction destination while the processor is in
the RUN mode. If a MSG instruction’s destination IP address changes, the
next time the MSG instruction executes, a new connection is established with
the new destination node. The old connection remains open as long as either
another MSG instruction was sharing it, or the connection inactive timer has not expired.

In addition, when a MSG is in progress and the ladder program
wishes to terminate it for any reason, this may be done by enabling
the time-out bit (TO = bit 8). The next time the processor scans the
MSG instruction with the TO bit set, it will error the MSG (ER = 1).
The MSG instruction may then be re-enabled with a false-to-true
transition on the next program scan.

Page 305
http://rockwellautomation.custhelp.com/ci/fattach/get/20327/1228705762

TIP
If the Target Node faults or power cycles during this time
frame of a MSG transaction, you will not receive a reply. As a result, use a MSG Timeout value in your MSG instruction.


 
todster said:
Inactivity Timeout:
The amount of time (in minutes) that a MSG connection may remain inactive before it is
terminated. The Inactivity Timeout has a 1 minute resolution and a range from 1 to 65,500 minutes. 30 minutes read/write(Default)

Aha! I think that's the information I needed. Thanks very much. Now I need to figure out where that value is stored/edited, so that in the future (or even programmatically) I can change this value when all the connections are used up...

EDIT: Okay, I find it on the CH1 configuration and it cannot be changed at run time...nonetheless, it is good information to have.

Mine is set to 30 minutes. I bet I was within 5 minutes of having the problem clear up on its own yesterday, but I didn't know it...

Thanks again.
Paul
 
Last edited:
Glad to hear it was useful. I haven't taught myself that yet,just read alot, but hope to once I find some AIC's for my 5/04 and 5/01 that are priced right.
 
Okie, I'm not big guru in EthernetIP but at some point tech. support told me the number of phisical connections is not the same as number of logical EthernetIP connections. May be you was exceedeng logical connections limit?
 
Okie, I'm not big guru in EthernetIP but at some point tech. support told me the number of phisical connections is not the same as number of logical EthernetIP connections. May be you was exceedeng logical connections limit?

Yes. This particular 5/05 has a 16 connection limit, and it's not Ethernet I/P, rather just plain old ethernet (I am sure there is a more accurate way to term it...)

I am still pretty green with ethernet stuff, but between this forum and rtfm, I am gradually gaining enough information to be less dangerous.
 
Now I need to figure out where that value is stored/edited, so that in the future (or even programmatically) I can change this value when all the connections are used up...

You might be interested in page 293 from the second link.
You'll probably want to parse the entire Chapter 12.
On page 276 it looks like you only get 8 connections, unless your processor is different than a 551B
 
Interesting.

I believe mine supports 12 incoming and 4 outgoing...perhaps the manual is not accurately reflecting the same firmware I have.

Right now I show 6 incoming and 2 outgoing, and yesterday, it showed 12 incoming and 4 outgoing when I had the error.
 

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