It contains fields confirming the action taken, any data to be returned, and an error-checking field. The slave's response message is also constructed using Modbus protocol. Modbus Organization'> 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. Slaves return a message (response) to queries that are addressed to them individually. The master can address individual slaves, or can initiate a broadcast message to all slaves. The other devices (the slaves) respond by supplying the requested data to the master, or by taking the action requested in the query. 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.ĭevices using MODBUS communicate using a master-slave technique, in which only one device (the master) can initiate transactions (queries). 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. Depending on the application a newer protocol may have more advantage. It is widely used and a fairly simple protocol.

MODBUS is a common means of gathering data from many different sources for viewing operations, archiving and troubleshooting from a central remote location. It was originally designed for Modicon (Schneider Electric) PLCs but has become widely used by many PLC manufacturers and industrial networks. It allows the exchange of data between PLCs and computers.

MODBUS is a commonly used industrial communications protocol.

Is modbus poll limited to address 49999