# Modbus

Note: This feature is only available if the optional Modbus plugin has been selected for installation in the Cognex Designer setup.

The Modbus plugin enables communication between Cognex Designer and external hardware using the Modbus protocol, a general purpose communications protocol used to communicate with a variety of hardware, including PLCs, HMI displays, and robots.

Modbus is simple and robust, and it is commonly used for connecting industrial electronic devices. It is a serial client/server (master/slave) protocol for industrial automation systems, and is an industry standard method to transfer discrete and analog I/O information and register data between industrial control (client) and monitoring (server) devices. When using it in a client/server infrastructure, the client device initiates transactions, while the server devices respond by supplying the requested data to the client, or by taking the action requested in the query.

While Modbus has several versions, the Cognex Designer Modbus plugin works over TCP/IP only. This implementation is simply the Modbus protocol with a TCP interface that runs on Ethernet. Hereafter, "Modbus Protocol" will refer to the Modbus TCP Protocol.