Serial to Ethernet converters can come in different varieties.
Serial to Ethernet Connector that allows you to work with Modbus to Ethernet. It enables you to provide shared access to a local Modbus device over network, so other network users can reach its content and functionality as if it were attached directly to their machines. In a similar way, you too can access a remote Modbus over Ethernet regardless your physical proximity to the device. Some converters, such as Lantronix, will simply receive serial data, encapsulate it in a TCP packet and send it to the desired IP address. In this case, the underlying Modbus protocol is still the serial "Modbus RTU" or "Modbus ASCII". You will want to use the "0 RTU (CRC16)" or "1 ASCII (LRC)" format in your Modbus Unit configuration for the MatrikonOPC Server for SCADA Modbus. If you are using the MatrikonOPC Server for Modbus (non SCADA) you will want to use the "TCP/IP Terminal Server". Some converters, such as Moxa and Garretcom, will go one step further and convert the Modbus protocol from Modbus RTU to Modbus TCP. This is useful in cases where multiple masters, such as redundant OPC servers, need to access the data. Modbus TCP differs from Modbus RTU, in that its messages do not use a CRC/LRC, and each message is prefixed with a 6-byte header. Make sure you choose the format "2 RTU TCP" in the Modbus Unit. If you are using the MatrikonOPC Server for Modbus (non SCADA) you will want to use the "Modbus Ethernet PLC (TCP/IP)".
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