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).