Flexy FLA3301, duplex modes


@Tim_hms, I found this reply on another thread and want to be clear in my understanding of the half- vs. full-duplex requirement of the RS232 mode of the serial ports. We are connecting a serial port of the eWON extension card to a Modbus slave which does not specify whether the mode, half- or full-duplex, may be set. We are only reading values from the slave which, I believe, effectively forces a half duplex mode, correct?

Out of curiosity, on the setup of the MODBUS IOServer, Half Duplex is an option. Why is that provided as an option when the RS232 of the eWON requires that the connected device be full duplex?

No, that’s not correct. Modbus is a bi-directional protocol, whether you are sending read or write commands.

If the slave is RS-232, it’s almost surely full duplex. It just doesn’t mention full duplex because that is generally assumed with RS-232.

Good question. We would have to ask the developers, but it’s not necessarily relevant to what you are doing so you can proceed with selecting “Full Duplex”. I would assume it’s because RS232/485 is not selectable on this page and is set by the dip switches and the settings in the Setup > System > Communication > General > Serial Ports section.

Thank you for the explanation on the duplex modes. We have connected to this slave device with a Modbus device other than an eWON so we’re fairly certain we can communicate with it via the eWON, just need to get the setup all in order.

You’re welcome!

Here are some more things to consider:

Please follow the IG-0016-00 - FLA 3301: 2 Serial Ports manual for installing the serial card and setting the dip switches (if necessary - you can use port S2 which is only RS232 if you want).

Follow AUG-0080-00 - Poll data from Modbus RTU for instructions on how to configure the serial card in the Flexy and the Modbus master.

Please let us know if you have any other questions.

Best Regards,

Kyle Reynolds