E - VAE ProSys sro

6.1.3 Address declaration for Modbus6.1.3.1 GeneralThere are two options for controls using Modbus RTU Protocol:• Modbus RTU Master• Modbus RTU SlaveTerminal operating as master− point-to-point coupling− read and write in any memory area− active reading of all data− automatic conversion of variablesTerminal operating as slave− Networking of up to 31 terminals to one master− automatic conversion of variables− Terminal reacts to send and fetch telegramsNecessary master operations− cyclical request of function keys and acknowledgements (time-out = 10s)If the timeout is overstepped the error message appears:"No function key data request"Telegram structure:• Function code 03 "Read one or more output registers"• address for exampleModicon 40001Telegram address 0• number of registers = 16If the area of time registers is not needed then a request of 10 registers is sufficient− spontaneous or cyclical sending of control words, message register and variables• Function code 16• address for exampleModicon 40020telegram address 19• number of registers = 23 + 6 (clock) + variables− spontaneous request of modified variables• Function code 03 "Read one or more output registers "• address for exampleModicon 40050 (Variable 1)telegram address 49• number of registers = 1Process display and control/ Device Manual/ Issue: 07.0195E