4/20/2016 12:13 PM | |
Joined: 1/17/2007 Last visit: 5/8/2024 Posts: 1542 Rating:
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Modbus TCP, Modbus RTU and Modbus RTU over TCP are all different protocols and are not compatible. Modbus TCP and Modbus RTU / Modbus RTU over TCP share the same Protocol Data Unit (PDU) but have a different Application Data Unit (ADU). Modbus TCP ADU is made up of: MBAP header + PDU. Modbus RTU ADU is made up of: Slave address + PDU + CRC. Modbus RTU over TCP, takes the whole standard RTU ADU (as used on serial RTU networks) and sends this over TCP (basically putting the RTU ADU inside a TCP wrapper and transferring it over a TCP interface). The receiving end must then extract the RTU ADU from the TCP layer and pass it to the serial RTU device on the serial network. I too have come across this requirement. I got round it a different way. What I used was a Modbus TCP to Modbus RTU convertor. Then used the standard Modbus TCP driver at the S7 end. Note: this is a Modbus TCP driver not Modbus RTU over TCP. The device I used was a Lantronix XPress DR-IAP (http://www.lantronix.com/products/xpress-dr-xpress-dr-iap/#docs-downloads). It is very easy to configure using a telnet or web interface. It comes with standard tunneling firmware fitted, which will need to be replace with the Modbus firmware. This firmware is downloadable for free from the Lantronix website. It is also very easy to install. This device is a Modbus TCP server on one side and a Modbus RTU master on the other side. My company has used this device (and still do) for many years on many jobs and it works very well. If you have any questions about the device then please ask away. Smiffy. |
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4/21/2016 3:49 AM | |
Joined: 11/21/2007 Last visit: 3/14/2024 Posts: 2323 Rating:
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We normally use Moxa MGate™ MB3180/3280/3480 Modbus TCP to Modbus RTU Convertors without any issues. AttachmentMGate_MB3180_3280_3480.pdf (377 Downloads) |
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