Modicon can mean Modicon PLC, the first programmable logic controller or PLC. The brand has gone through several owners and is now owned by Schneider Electric. Then now Modicon (Schneider Electric) was designed MODBUS as a commonly used industrial communications protocol. It allows the exchange of data between PLCs and computers. But it has become widely used by many PLC manufacturers and industrial networks.
MODBUS is a common means of gathering data from many different sources for viewing operations, archiving and troubleshooting from a central remote location. It is widely used and a fairly simple protocol. Depending on the application a newer protocol may have more advantage.
Typically a PC is set up running such programs as Wonderware, Intellution or LabVIEW in one location to gather data from various processes around the factory. Another application is for setting up remote factory process controllers (such as other PLCs like Allen-Bradley, Siemens, PLCDirect, etc.) to respond to different levels or modes that are being transmitted from the device.
Modbus protocol establishes the format for the master's query by placing into it the device (or broadcast) address, a function code defining the requested action, any data to be sent, and an error-checking field. The slave's response message is also constructed using Modbus protocol. It contains fields confirming the action taken, any data to be returned, and an error-checking field. If an error occurred in receipt of the message, or if the slave is unable to perform the requested action, the slave will construct an error message and send it as its response.