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I am battling to connect a Siemens KTP700 Basic DP HMI panel directly to a Emerson UniDrive via Modbus RTU RS485. in the manuals both devices can talk Modbus RTU. The two devices do communicate, but the connection drops after a few seconds and there is some strange PLC address error. I am using baud-rate 19200b/s, no parity and 2 stop bits. I have used function code 4x. The parameter in the drive is 06.15 and the address in the HMI is 400615. My wiring is such; Drive pin 3 (0V) = HMI pin 5 (0V), Drive pin 2 (TX/RX+) = HMI pin 3 (TX/RX+), Drive pin 7 (TX/RX-) = HMI pin 8 (TX/RX-). What could I possibly be doing wrong? As I don't know Modbus well!