Specifications

STB NIP 2311 Services
EIO0000000051 6/2010 117
A device may implement a Modbus client service, a Modbus server service, or both,
depending on the requirements of the device. A client is able to initiate Modbus
messaging requests to one or more servers. The server responds to requests
received from one or more clients.
A typical HMI or SCADA application implements a client service to initiate
communications with PLCs and other devices for information gathering. An I/O
device implements a server service so that other devices can read and write its I/O
values. Because the device does not need to initiate communications, it does not
implement a client service.
A PLC implements both client and server services so that it can initiate
communications to other PLCs and I/O devices and respond to requests from other
PLCs, SCADA, HMIs and other devices.
What a Modbus Client Service Provides
A device that implements the Modbus client service can initiate Modbus messaging
requests to another device that implements a Modbus server. These requests allow
the client to retrieve data from or send commands to the remote device.