MicroLogix 1100 Communication

I am trying to communicate with a MicroLogix 1100 by writing my own driver. I have successfully been able to connect and read values off of the PLC.

The problem I am having is that the PLC stops responding to my queries for data. For instance, if I query values in F8 with one packet, and then try to query F9 with another, it will not respond. The only way I can get it to query again is to wait a minute then reconnect. I see it communicating constantly to RSLinx so I'm not sure where the limitation is coming from.

I am using Ethernet/IP to communicate. I used some of the information here http://www.rockwellautomation.com/enabled/guides.html and from other sites to figure out how to communicate with the PLC.

It would be very interesting to me if you documented the time you spend on this effort. I've tried many times to quantify the "build vs. buy" decision on communications drivers but have difficulty getting accurate labor data.

Are you incrementing the Transaction Sequence Word (TNS) in the PCCC command? This is noted as "TNS1 TNS2" in the embedded PCCC command. If the controller gets a command with an identical TNSW value to a previous command, it will ignore the "duplicate" command. Some controllers can be configured to do this as an option, some cannot.

If you can post some TCPDump or Ethereal captures of your driver's traffic, others might be able to assist.

We weren't able to find a Java driver, maybe we didn't look hard enough. If I could find one of those I might take that route.

I've attached my capture file. I wasn't incrementing the TNSW at one point and changed that just to make sure, but it still reacts the same.


PS. Ethereal has moved to Wireshark

I figured it out, there was another sequence number besides the TNS that I wasn't incrementing.

I presume you mean the TCP Sequence Number ?

I don't ahve access to the TCP layer in Java. It was the Sequence Count that is before the Message Router Service Request in the Connected Message.

As far as time spent, I have a little voer 100 hours billed to this, but that also includes searching for existing drivers and researching plc communication.

So, in Ken's calculation, let's assume a cost (not salary, mind you) of $35.00 per hour. That means you have $3,500 invested in this project, and I suspect you have some more time to go.

So, what is the cost of a Kepware or RSLinx package?

Not sure about the cost of hee RSLinx SDK, they wouldn't give us much support on that. The costs that I believe I heard was $800 per copy of RSLinx. All we want to do is write a few values to the PLC. It really comes down to how many copies of RSLinx we would need, if we shipped 20 units, it would have included 1 extra copy each, thats $16,000. The work I have left is small, I have all of the packet structures comleted. I just need to successfully write to the PLC.

Could the Micrologix 1100 communicate using Modbus (I know the larger versions do, eg 1200 & 1500). If so I think you would find writing a modbus driver considerably easier, lots of example code around.