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rajsiyer

Lantronix XPress-DR

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Hi fellas, In my current project, I have a network of 3 PLCs & 2 HMIs all on Ethernet, with static IPs. There is a Lantronix XPress-DR gateway device, which is meant to connect one particular PLC to the serial (RS-422!) port of the Plant -DCS (Yokogawa) The DCS needs to read/write data over Modbus, from the PLC. My questions are.. 1. Is this Lantronix - XPress DR device capable of the above service.. ie. enable a serial port to look through a PLC on the ethernet IP? 2. If so, how does one configure the Lantronix device? Thanks a million for looking in, Best of luck.

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Took a look into the specifications right now. The Lantronix is indeed capable as a TCP/IP device server which means you can connect it to the Ethernet, and it will act as a serial server against your peripheral device. However it does not support ModbusRTU conversion between TCP/IP and serial which means that you cannot set up ModbusTCP on the client (Master) and expect the RTU slave to respond since the Lantronix does not do any conversion, it just wraps the serial data into a TCP/IP packet. You have two options: 1. Purchase a gateway device that acts as a ModbusTCP/Serial server - that way you can set up ModbusTCP on one side (Master/Client) and connect to a serial slave 2. Set up the master to do Ethernet tunneling against the Lantronix. This means that the master sends a serial telegram, the computer or similar wraps the telegram into TCP/IP packets, sends it to the Lantronix which unwraps the packets into the original serial telegram and vica versa. Let us know if you have any questions, and/or what you choose to do...

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Thanks friend, for your immediate response!! I am now trying to understand your suggestions... in this case, I don't know who is the master and who is the slave!! And tunnelling?? what is that? In my past experience with Serial -Eth. gateways (like Schneider's ETG-100) , it was the other way round.. ie the serial devices were the slaves! In the present case the master seems to be the DCS with a serial RS-422 port. That also means no multiple drops right. After reading your response, I've discovered that it is possible for 2 serial devices to talk over a LAN using 2 XPress DRs. Maybe this is relevant and simple to do. Thanks friend once again. Deeply appreciate your taking time to help. My best wishes that you do well.

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That sound like a very good plan!! You set both devices to talk serial, and the you set up the XPress boxes to talk to eachother... You will have to buy one extra box, but it will probably save you some hours of work... Let me know if I have misunderstood you.

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Dear Kaare, It seems I managed to confuse you. I apologize. Sorry. Actually the DCS is the only serial device. There is also only 1 Lantronix device. Our requirement is that the DCS must be able to read Modbus data from inside a PLC on the LAN. The link I sent shows an example of how 2 serial devices may be linked through a LAN, equivalent of wire them directly. In the example, the 2 serial devices, are each connected to a Lantronix device. The configuration of each device's serial port refers to a "remote-IP" address. I think it means that the serial port now behaves like it belongs to the device connected at the remote! In our case, a PLC is connected at s 192.168.0.10 and the DCS has a RS-422 port. I plan to connect it to a Lantronix device at 192.168.0.50 and configure its serial port as RS-422 and with a 'remote-IP' of 192.168.0.10 . I think this will cause the Lantronix port to behave as it belongs to the PLC itself. Do you think my understanding is correct?

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OK, do you have a spec on the DSC (brand, model+++) so I can check it out?

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DCS is Yokogawa Centum. Comms. Module I think is ALR121

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I took a quick look. You should really purchase a Modbus converter instead. Here's a few links to distributors of these kind of gateway's: http://www.advantech.com/products/Modbus-Gateway/sub_GF-5TZ5.aspx http://www.moxa.com/product/MGate_MB3170_3270.htm Let us know if you have any other concerns.

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You should be aware that Lantronix has a multitude of serial servers. I've used one is called Xpress DR-IAP with a specific optional component for packaging Modbus messages. I used Ethernet on the Modbus master side and serial RS-485 on the Modbus slave side to 3 or 4 slaves. It worked fine. Although the unit was purchased as a Modbus-enabled device, the Modbus component had to be loaded onto a standard Lantronix server unit via an installation file. That's the way they do it. I configured it with Telnet over ethernet. I found their pre-sales support very good. They're capable of assessing what is needed and clarifying which model is needed. I'm not sure that a serial Modbus master can use this particular device, because I can't recall any 'mapping' function to map a slave address to an IP address. How does the server convert an RTU message with slave address like 03 into an IP like 192.168.3.42? Going the other way, an Ethernet Master's message includes the slave device's address which gets unpacked and becomes part of the serial message. But the other way around? Maybe there's a mapping function but since I didn't need it, I missed it. Later posts in this thread seem to indicate some kind of mapping function, so maybe it's there. Please tell us what route you take and how it works out.

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Thanks Dan, & Kaare too.. Actually, I've learnt that all this and more are possible. It is no longer a case that "only" serial slaves have sit behind a Gateway. So also, no longer is the case that only ethernet devices need to be masters! The only constraint here.. is that whilst a RS-422/485 device could be a master to 'a' TCP slave, it cannot be masters to other multi-dropped serial slaves on another Lantronix device server. Mapping is achieved by assignment of a remote IP address to the No.2 serial port, in additon to serial-comm parameters. This way the rest of the network sees the serial device as another TCP host. Yes for all the above, one has to change the IAP firmware to Modbus. And you're right about Lantronix.. their geeks are very competent and prompt in helping. For what it is worth I post the following links. 1. XPress+ User Guide 2. Modbus protocol user guide. 3. You need DeviceInstaller as Lantronix webManager is not to be used. 4. Firmware ROM file. I need to go again to site and do all this. When I am done I'll report what happened. Thanks and regards

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