MODBUS communication


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I am using MODBUS TCP protocol for communication between two devices. Daqfactory software is then used to access one of the devices which is defined it in the quick configuration of daqfactory.

The problem am having is the Rx returned in daqfactory. One of the device is connected to the other and it uses MODBUS to communicate with the polling device, daqfactory then initiates the polling request to the polling device which then request data from the other device.

For every register of the device i try to read in daqfactory the Rx returned is 00. However the Tx and Rx LED of the polling device flashes in turn and sequentially indicating data exchange between the two devices. But the Rx data showing in daqfactory is 00 which is not the expected result of the read register.

Could you kindy point me in the right direction as i cant figure out why the returned data is always 00.

Thanks in advance.

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Unfortunately this is a device or device configuration issue so I can't say much. DAQFactory just displays what it receives. 00 is typically the first byte returned from ModbusTCP, but it also could just be garbage. Anyhow, I'd first try disconnecting one of the devices and just communicate with the other alone from DAQFactory.

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  • 3 months later...

Are you using a TCP to Serial Adapter????

Normally i don't see Rx Tx Lights on a TCP Device???

If you are check your Baud rate etc and try simply try opening a web page to the TCP address.

Some Devices we use have 'TCP' but are actually Serial Device's with a TCP adapter so when you change the controller Baud rate it all goes wrong, unless you log into the web interface of the device and reconfigure it.

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