Modbus TCP is an Ethernet implementation of the widely supported, widely used Modbus RTU protocol. Modbus RTU is the easy-to-implement Master/Slave communications protocol built by Modicon in the late 1970s. Modbus RTU achieved incredible penetration to many markets and applications because of its sheer simplicity. With a very small command set, easy to understand network representation and simple Request/Response message structure it became the defacto leader for communications between industrial devices. The biggest advantage for vendors implementing Modbus RTU is that is required no additional hardware other than a serial channel and a RS485 driver chip. Adding Modbus RTU could be accomplished with little expense but end users suffered with very low throughput, troubleshooting and sometimes non-standard driver chip implementations.
Modbus TCP corrects those problems. Building on the simplicity of Modbus RTU and the desire for many customers to use Ethernet, Modbus TCP was created. Modbus TCP uses the identical command set, addressing modes and network representation as Modbus RTU. Effectively the same message that is transferred over RS485 using Modbus RTU is sent over a TCP/IP connection using Modbus TCP. Only the error checking bytes are eliminated as they are provided at the physical Ethernet layer. Using the identical message structure and network representation enabled many uses to move their RTU applications to Ethernet.
You can now add Modbus TCP Client communications to your product quickly and easily with the Modbus TCP Client and Client development kits from Real Time Automation, Inc.. Developed specifically for industrial platforms and fully integrated with any number of RTOS systems and TCP/IP stacks, you can have Modbus TCP Client communications in days not weeks, months or years. The development kit includes everything you need to implement your Modbus TCP networking solution; "no royalty," single task source code, sample objects, PC Tools, a ready-to-run sample application, complete documentation and much more.
Modbus TCP Application Diagram