Hello,
We have a counter that its output is Modbus RTU (serial) and is connected to a serial-to-Ethernet converter (Moxa nport 5110). A SCADA is reading the data of this counter through the Moxa. Now we should read data of this counter through this moxa in ignition. The question is that can we use Ignition Serial Module to read the data? is it possible that both system (the other SCADA and Ignition) reading simultaneously the data of this counter ?
I’ve had some success with the Modbus driver + the serial support module doing exactly this with the Moxa nport (I don’t remember if it was the 5110…). When those two modules are both installed, the Modbus driver offers “Modbus RTU over TCP”. Note that it is fragile – only one SCADA can talk on the serial port, and any framing errors cause brief stalls. Consider a Modbus TCP to Modbus RTU gateway product instead, such as Moxa’s MB3180.
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Thanks for your reply. I tried with “Modbus RTU over TCP” and the module is connected but I cannot read any data (the tags shows BAD DATA) while the other SCADA system is reading the values correctly and that’s why I thought I may connect to the MOXA with Ignition Serial Module. When you said it’s fragile, you meant now that the other SCADA system is reading the data I cannot read the data from Ignition simultaneously? about considering other gateway, I cannot replace this MOXA with others because of some limitations and I need to figure out a way to read the data with this MOXA. Do you also have an example or document how to read data with serial module?
You won’t be able to read data from this with the serial, either, if another SCADA system is already polling it.
You can’t have multiple systems accessing a device on same serial line unless you put a real Modbus gateway in front that will mediate access to the serial line.
So there is no way to read the data from this MOXA (either with Modebus RTU over TCP module or Serial Module) if another SCADA is polling the data? the only way is to replace the MOXA to a Modbus gateway (e.g. MGate)?
Yes, that’s correct.
If the other SCADA system has an OPC server you could connect Ignition to that and read the data it’s polling from Modbus indirectly.
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Ah OK thanks Kevin. Just for the curiosity: why the Module “Modbus RTU over TCP” is on “Connected” status if it cannot make a proper request (reading the data) to the serial line behind the MOXA?
Because it has an open TCP connection to the MOXA just fine.
It will attempt to read any tags you’ve set up, and might even work occasionally, if the timing allows for the request and response from Ignition to hit the serial line in between the other SCADA system polling. But it will be unreliable.
Just in case, if we replace the current MOXA Nport with MGate MOXA that converts Modbus RTU to Modbus TCP, in this case both Ignition and the other SCADA system can work and read the data of the counter simultaneously without any problem?
Yes, assuming the other SCADA system can be modified to use regular Modbus TCP instead of RTU over TCP.
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