Connecting Delta SV2 PLC Using Modbus

The manual here eng.pdf
states on page 9 that the device can only reply with one variable per Modbus message/transaction using Function Code 03 (read Holding Register).

The RS-485 wiring has Sg (signal ground) driver lines A and B, and a terminal for TR. I suspect TR is terminating resistance, but it connects to the A driver on one slave device only. Who knows?

Furthermore, that document does not have a Modbus slave table of registers/ addresses and the associated units for the data values. I'd want to find that document before I spent one minute on anything else Modbus.

To connect, you need a Modbus Master, because these are slaves.

It appears that the manufacturer offers a software package. eng.pdf
You might want to see what that software does and whether it meets your needs before struggling through a Modbus implementation.