Hello, I have small project do control Schneider VFD Altivar 320 with 750-8102 over modbus RTU.
I have connected device to RS485 and when I read holding registers I get error CRC checksum fail or invalid data response. Comm setting are correct. Devices are connected with 0.5 meter cable without termination. I have wired rs485 pin 3 to RJ45 connector on Altivar VFD to D1 and pin 8 to D0.
Is it correct wiring or I need to jump wires on rs485 connector? Can anything else be problem ?
I haven’t checked your pin assignment, but I would try with termination including the pullup / pulldown resistors. I’ve had problems with rs485 where my equipment have recieved the wrong data because of the small electrical disturbances when switching between sending and listening. The easiest way to add the right resistors is to use a contact for profibus like 750-960.
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Hello,
i have purchased Wago profibus connector.
Can you explain proper termination insert on connector?
It’s easy. You just activate the termination with the little switch on the contact. then you get ok resistors between A & B plus resistors to 0V and 5V as well.
in built-in RS-485 you need to terminate it in controller side. 120-150 Ohm between 3 and 8 pin.