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Using PG2000 you can establish online connection and check on Target -> Monitor to see what's running on the machine.

1. Automation Studio 2. B&R serial programming cable (please check manual) 3. Download Automation Studio with 30-day trial license from the website http://www.br-automation.com/en/downloads/#categories=software/automation-studio You can download System 2003 manual from the website http://www.br-automation.com/en/downloads/control-and-io-systems/system-2003/system-2003-users-manual/

Why don't you try asking them directly?

RS485 can cover a distance of up to 1,200m (at 100kbps), shorter distance for higher data rate.

Thanks for your input, Mark. Obviously I'm quite new with this stuff. I'm not sure what 'socket' thing you're referring to but the PLC I'm working with right now only comes with one Ethernet port configurable for Modbus TCP. I follow your suggestion to break up the slaves into smaller groups but I'm not sure how to create the table you mentioned so I put error counter instead. After 10 error counts I disable the polling of that device until it reaches 30 counts when the PLC retries polling again and the counter resets. The lag is still there during initial scanning and retries but I think I don't have choice on this, do I? By the way the 'hang' issue turns out due to 'cycle time violation', i.e. the running time of my polling task exceeds the task class cycle time, which I think it's due to time outs from many dead slaves. I'm using B&R PLC, the 70x meters are modbus RTU connected to 7x data concentrator cum modbus TCP gateway, the 50x digital input modules are connected to 4x modbus TCP/RTU gateways as well. So practically my overall speed is capped to RTU, which is set to 9600bps.

Thanks for the reply. I'm polling 120 slave devices comprising meters and digital inputs. In commissioning I don't have control to make sure every slave device is alive. As my PLC is continuously polling, those devices which are not powered up would slow down the polling process and eventually causing the PLC to hang. Is there any workaround so that the PLC will just skip those dead devices and continue polling the rest? My error handling is to handle exception from the slave, but how to handle if the slave is not even alive? Currently my refresh time is 100ms and refresh time violation is 500ms. Thank you for any suggestion.

Hello, can a Modbus TCP be event driven? I.e. rather than cyclic updating of Modbus data, the Modbus data is updated only when the data is changed.