Modbus is the name for a data communication protocol developed in 1979 by Modicon for its automation systems and PLCs. It has become an industry standard to transfer discrete and analog data between industrial control and monitoring devices and computers. Modbus is now an open, widely-accepted, and public-domain protocol that requires a license, but does not require royalty payment to its owner.

Modbus devices communicate with the master-slave (or client-server) communication method. Only the master device (or client device) can initiate the data transactions (or queries). The slave device (or server device) responds to the queries by supplying the requested data to the master device or by taking the actions requested in the query.

A Modbus slave is usually a sensor, a valve, a single-loop controller, a PLC, or a DCS. A Modbus master is usually a host computer running application software. But there are exceptions. For instance, the Delta V DCS by Emerson provides Modbus serial interface but it is a Modbus Master.

• RS-232/RS-422 serial communication standard, and
• TCP/IP network communication standard.

Modbus TCP implements the Modbus RTU protocol utilizing the TCP/IP communication standard enabling two Modbus-TCP devices to talk over the Ethernet.

• CyboLink Modbus Serial
• CyboLink Modbus TCP

CyboLink Modbus Serial Interface software provides solid 2-way data communication between a Modbus Slave or a Modbus Master device with CyboCon software through a serial port. CyboLink Modbus TCP Interface software can connect Modbus-TCP supported devices to a CyboCon PC via the Ethernet network, which can be wired or wireless LAN/WAN. For both products, Modbus PLC types supported include 384, 484, 584, 884, M84, 984, and Quantum.

With easy Graphical User Interface of CyboLink, configuration is a snap! In fact, you can learn and test the Modbus interface using 2 CyboLink Modbus Serial or TCP software products on 2 PCs, one set for Master, and the other set for Slave.