RuggedCom RS400 manual Modbus Server and Client Applications, TCPModbus Performance Determinants

Serial Protocols

2.2.2 Modbus Server and Client Applications

The Modbus Server and Client applications are used to transport Modus requests and responses across IP networks.

The Modbus Client application accepts Modbus polls from a master and determines the IP address of the corresponding RTU. The client then encapsulates the message in TCP respecting TCPModbus protocol, and forwards the frame to a Server Gateway or native TCPModbus RTU. Returning responses are stripped of their TCP headers and issued to the master.

The Modbus Server application accepts TCP encapsulated TCPModbus messages from Client Gateways and native masters. After removing the TCP headers the messages are issued to the RTU. Responses are TCP encapsulated and returned to the originator.

The following figure presents a complex network of Client Gateways, Server Gateways and native TCPModbus devices.

Figure 34: Modbus Client and Server

2.2.2.1 TCPModbus Performance Determinants

The following description provides some insight into the possible sources of delay and error in an end-to-end TCPModbus exchange.

RS400 59 ROS™ v3.5