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TCP/IP to Serial Modbus?
I have a PLC that I am trying to communicate alarms to an annunciator.

The PLC protocol is Ethernet TCP/IP. The Annunciator is Serial Modbus over ethernet. From what I have been able to figure out I'm going to need an adapter to get these to communicate? Working with a Moticon M340 and a Ametek Annunciator. The annunciator does not support Ethernet TCP/IP and from what I have read the Moticon only communicates in TCP/IP. Any suggestions?

You want a "Modbus gateway" or "Modbus Ethernet gateway". Try either of those and you will come up with lots of sources. This is a very common requirement and there are lots of devices available that do that. Your PLC vendor many have one.

They are typically a small box with an Ethernet port and one or more RS-232 and/or RS-485 ports. They simply pass the Modbus messages back and forth between the serial and Ethernet networks, while performing the proper conversions (the message headers are slightly different). Different models have different features and degrees to which they can be configured to handle special situations, so you will probably want to look a few of them.

You can use Sibotech gateway.

Product type:ENB-302MT ENB-302MI

Company: SiboTech Automation Co., Ltd.

SiboTech supply multi-gateways, and support communication protocols: DeviceNet, Profibus-DP, CANopen, Modbus, EtherNet IP, Mobus TCP and so on.

Sibotech help you connect your field devices to different control devices: PLC, DCS and so on.

Schneider Electric has proven bridges to connect Modbus TCP/IP to Modbus serial (RS232 or RS485) devices. Schneider Modicon controllers provide Modbus TCP/IP,Modbus serial (RTU/ASCII 232/485 Host/Slave)and other protocols. Why not directly contact your local Schneider office or distributor for a solution.

By Darrin Hansen on 28 April, 2010 - 8:57 am

The ICC ETH-1000 gateway support both Modbus TCP client and server as well as Modbus RTU master and slave. It's also configurable via USB.


The FieldServer bridge converts Modbus serial to Modbus TCP/IP. Depending on the FieldServer model you select, the FieldServer bridge can handle conversion (mapping) of 500; 1,000; 5,000; +10,000 points. Visit for more information.

A small Modbus TCP to Modbus RTU (binary serial) converter is I-7188EX-MTCP, see

The M340 already has a Modbus serial port. If it's not used for anything else, you can connect the annunciator directly to that port. That's fairly simple *if* the annunciator is a Modbus master. No programming in the PLC would be required.

If the annunciator is a Modbus slave, you have some work to do in the M340. You can use the WRITE_VAR function to update the annunciator directly over the M340's serial port, you can use the WRITE_VAR function to update the annunciator from the Ethernet port through an MEB, or you can install an NOE (the expensive one, I forget what the part number is) that will support Modbus/TCP I/O scanning through an MEB.