CLX communication with Prosoft PLX over modem

[lhwdtech]

We have two sites that are stranded with no line of site, they are handled by phone/modem with a chain that includes:

Stranded site (client) CLX--> ethernet protocols-->Prosoft PLX-51 ENI (bridge mode)-->serial com-->Miille modem-->phone line-->Miille modem-->serial com---> Prosoft PLX-51 (bridge mode)-->ethernet protocols--->to the server CLX.

We are writing to the server (plant) and requesting read data. Currently, we are able to receive the write data from the client, but the read responses are not being sent back to the client sites. In the packet monitors on board the Prosoft PLX, we see the write file come in and gets ACK, a read file comes in and gets ACK, but data does not go out. Currently trying SLC5 message types. Have also tried timing outgoing messages from the server while the connection is established and they do not seem to make it out either.

The previous system had an SLC 04/05 at the server (plant), with an onboard modem, but was hit by lightning a couple months ago. As the SLC 04/05 is slated to be upgraded with the plant in 6-10 months and the rest of our system is already on CLX, we decided to look forward instead of replacing the old unit. With the old unit, we had no issues with communicating read/ writes, but this is only communicating one way.

Appreciate you folks taking a moment out of your day to think about this, if I can't find anything, I may have the system monitor tag changes to determine site, or have it communicate a register to identify the site and then a timer to call the site back and see if the one way communication would work in that manner, but it sure would be nicer if we could just take care of this in a single full duplex call.

 

[Ken Roach]

Welcome to the PLCTalk forum community ! You've brought a head-scratcher for your introduction but you've also got more than the usual diagnostic tools.

You're using SLC-500 style data table addressing, so you must have the necessary Data Table File numbers configured to correlate with INT[x] type array tags in the "Server" ControlLogix.

Double-check the size of the INT[x] array tag to be sure it can support all possible N:x or B:x offset values, and also check to be sure that external access is allowed for the INT tag.

>A read file comes in and gets ACK but data does not go out

Are the PLX-51's set up for DF1 Half Duplex or Full Duplex ? I think there should be a separate ACK only if it's half duplex.

Do you have the ability to sniff the Ethernet traffic between the PLX-51 and the Server CLX ?

 

[lhwdtech]

Thank you Ken, the folks at Prosoft and the modem company doubt that anyone else in the US is doing this, so it kind of puts us on an island.

Our SLC message arrays are set up the same, on both sides, regarding size of the array tag, and both sides are set up for External Read/Write access.

>Are the PLX-51's set up for DF1 Half Duplex or Full Duplex ? I think there should be a separate ACK only if it's half duplex.

Full Duplex, and that ACK has thrown off the Engineer at Prosoft as well, it's kind of strange.

Yesterday, for grins, I put two of the station, one client and the server, into "Radio Modem" mode instead of full duplex. Some interesting things happened,

1. I never lost the communications between any of the sites, even the site I did not change

2. It got rid of the ACK and bouncing ENQs (3-6/ transmission) that would follow each “Protected Logical Write” and “Protected Logical Read”, now the only thing after a Read or Write is a “success” reply.

3. My source changed on the client end, from the PLC node address to the PLX-51 node address, both on the logs at the client and the server. I even added the node additions into the CIP address on my message instructions, but still do not see the message from server go to the client.

Our Hex data on the logs at the PLX looks good, I will see about getting some images uploaded to the web to share. I just don’t think that there is anything leaving the server PLC, we never see any data on the PLX logs indicating anything from the PLC node aside from the ACK or success replies, even when I send writes from the server PLC.

Thank you for the idea of the packet sniffer, I am going to pick one up. Was already in conversation with Prosoft engineers to set up one computer as a wedge, run a script and monitor the serial traffic. Only makes sense to just add the extra layer and monitor the ethernet end at the same time, gain the full scope.

 

[TheWaterboy]

Make sure the firmware in the PLX is the latest. v10 or 11 at last memory. I discovered (and Ken decoded ) that their firmware was not handling serial properly. It was ignoring TNS and would reassemble packets out of sequence causing them to just be dropped. I was using the PLX51-DF1-ENI (v1.003) at the time but its worth thinking about.

If you are talking to Larry at Prosoft he will get you there eventually, but that is one overworked dude so you need to prove your case with evidence to get quicker results. Once I presented them with my symptoms, ethernet and serial trace files, and Kens evaluation of them I had a fix within a couple days and v10 of the FW was born.

 

[lhwdtech]

TheWaterboy- "Larry is overworked" seems pretty spot on, he has been with me since the I first submitted a ticket. It's pretty cool that you guys were a big impact on a major firmware version.

Updated to the current firmware version about a week ago, and it did straighten up a weird addressing issue. Before the firmware update, it was displaying that the source and destination were the same thing, in this case SRC-4 DST-4, but of course was still passing through the data from client to server. Now that issue is cleared up, but we still aren't communicating back to the client.

 

[TheWaterboy]

I don't know how major the release was, a mistake like that should not have even been possible so it was just a poor software design.

In my case I was polling a series of endpoints over radio and the response received would appear to be coming from the previous polling connection under the right conditions. So I was asking Fred for info and Wilma appeared to be the one that responded. Sounds similar enough.
My route is CLX -- Ethernet -- (IT security and witchcraft) -- PLX51 -- Radio -- RF -- Radio -- PLC5 Serial port (DF1)

Can you ping each direction? ( I wonder what that's like over a modem...)
Can RSLinx see the endpoint and return data?

Wireshark will be your friend here. Its possible there is something blocking the ethernet traffic.