24-04-2014, 12:20 PM
INTRODUCTION TO MODBUS TCP/IP
INTRODUCTION
The Modbus protocol was developed in 1979 by Modicon, Incorporated, for
industrial automation systems and Modicon programmable controllers. It
has since become an industry standard method for the transfer of discrete/
analog I/O information and register data between industrial control and
monitoring devices. Modbus is now a widely-accepted, open, public-domain
protocol that requires a license, but does not require royalty payment to its
owner.
What is Modbus?
Modbus devices communicate using a master-slave (client-server)
technique in which only one device (the master/client) can initiate
transactions (called queries). The other devices (slaves/servers) respond
by supplying the requested data to the master, or by taking the action
requested in the query. A slave is any peripheral device (I/O transducer,
valve, network drive, or other measuring device) which processes
information and sends its output to the master using Modbus. The Acromag
I/O Modules form slave/server devices, while a typical master device is a
host computer running appropriate application software. Other devices may
function as both clients (masters) and servers (slaves).