• This gateway can read Modbus data from your Modbus RTU devices and publish it as Modbus TCP data.
• It can also write to the Modbus RTU devices.
• This gateway can also do the reverse, read Modbus TCP data and publish it as Modbus RTU data.
• It can also write to the Modbus TCP devices.

In summary, this gateway can act as:

• Master on the Modbus RTU network: Hence it is capable of reading data from the various Modbus slave devices and writing data to them if required.
• Slave on the Modbus RTU network: You can use the gateway in this mode if you have a Modbus RTU master on the network which would be reading data from the gateway.
• Master on the Modbus TCP network: Hence it is capable of reading data from the various Modbus TCP devices and writing data to them if required.
• Slave on the Modbus TCP network: The gateway can be configured to be a server of data values, hence another Modbus TCP client can read data from the gateway and write data into the gateway.

• On a site you have several Schneider Ion energy meters that can provide data output on Modbus RTU.
• The site has a SCADA on Modbus TCP that needs the data from the Ion meters on Modbus RTU.
• Since the Schneider ion meters provide data output on Modbus RTU and the SCADA understands only Modbus TCP a direct data exchange is not possible.

Solution:

The devices can not directly communicate with each other as they are not on the same protocol. Modbus RTU is a Serial protocol, while Modbus TCP is an Ethernet based Protocol. You need something that will convert data from Modbus TCP device to Modbus RTU and vice versa.

ProtoConvert’s Modbus RTU to Modbus TCP converter will be an excellent solution for this requirement. The gateway reads data from the Energy meters on Modbus RTU. It caches this data internally and then provides it on Modbus TCP when requested from the SCADA system.

• On a site you have several variable frequency drive that can provide data output on Modbus TCP.
• The site has a PLC on Modbus RTU that needs data from Variable Frequency drives on Modbus TCP.
• Since the Variable frequency drives provide data output on Modbus TCP and the PLC understands only Modbus RTU a direct data exchange is not possible.

Block Diagram:

Solution:

The devices can not directly communicate with each other as they are not on the same protocol. Modbus RTU is a Serial protocol, while Modbus TCP is an Ethernet based Protocol. You need something that will convert data from Modbus TCP device to Modbus RTU and vice versa.

ProtoConvert’s Modbus TCP to Modbus RTU converter will be an excellent solution for this requirement. The gateway reads data from the Variable frequency drive on Modbus TCP. It caches this data internally and then provides it on Modbus RTU when requested from the PLC.

Modbus RTU:

ModbusRTU is a serial communication protocol that connects different devices on the same network and would make the communication between them possible.

Modbus is transmitted over serial lines between devices. The cables used for the conecction are either RS-485 or RS-232 cables. The simplest setup would be a single serial cable connecting the serial ports on two devices, a Master and a Slave.

The data is sent as series of ones and zeroes called bits. Each bit is sent as a voltage. Zeroes are sent as positive voltages and ones as negative. The bits are sent very quickly. A typical transmission speed is 9600 baud (bits per second).

Modbs TCP:

ModbusTCP covers the use of Modbus communication via an 'Intranet' or 'Internet' environment using the TCP/IP protocols. The most common use of the protocols at this time is for Ethernet attachment of PLC's, I/O modules, and Gateways to other simple field buses or I/O networks. 
There will always be this question why the connection-oriented TCP/IP protocol is used rather than the datagram-oriented UDP. The Primary reason is to keep control of an individual ‘communication’ by isolating it in a connection which can be identified, cancelled , and supervised without the need of specific action on the client and server applications. This gives the mechanism a tolerance to network performance changes, and also gives a scope to add security features such as firewalls and proxies. 
MODBUS/TCP/IP handles two different situations. A connection can be recognized too easily at the protocol level. A single connection can be used to carry out multiple independent communications. To add to it, TCP/IP allows a huge number of concurrent connections, so the user decides to re-use an old connection or reconnect to a frequently used connection.

The Modbus device can be connected using an Ethernet port on the gateway. We can make a query using any standard Modbus Scanner to extract the value from a Modbus device. All requests are sent via TCP/IP on registered port 502.