Modbus slave communications

[Matt]

I am using a T100MD1616+ PLC as a modbus Slave to a Eurotherm 5000B Data Acquisition Unit being the Modbus Master.My Question is do I have to use the writemodbus command in my plc program to send the data or will the master automatically querry the data from the [DM] holding registers in the plc. If anyone has tried this application before I would greatly appreciate your help.

[support]

Yes, you can use your DAQ as MODBUS master to talk to the T100MD1616+ as modbus slave. The communication occur in the background and is completely transparent to the PLC program. i.e. you PLC program doesn't need to do anything for this to happens (as long as your PLC program is not interfering with the comm by writing out to the COMM port). In fact, it will work even if you put a blank program in the PLC.