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RS-485 Checklist

Owned by Dirk Conzelmann, created
Last updated: 16.Sept 2024
1 min read

 Problem

You want to communicate over Modbus-RTU and there are suspicious errors. The underlying bus is RS-485.

 Solution

There is only one Modbus Client on the RS485 bus
There is one bus with two ends without Y-branch
There is a bus termination of 120 Ohm at both ends of the bus. The following modules contain an activatable terminating resistor: RevPi Connect SE, RevPi Connect and RevPi Connect S:
https://revolutionpi.com/en/tutorials/serielle-geraete-anschliessen-compact
https://youtu.be/guzrFgp7Sx8
The P and N lines are correctly wired at all communication partners
The baud rate of the communication partners is known and correctly set at the Modbus Clients and all Modbus Servers
The parameters of the serial connection are known and correctly set by each communication partner:
baud rate
parity
start bits
stop bits

Take a look at the Tutorial 21 – Modbus RTU Master https://revolutionpi.com/tutorials/video-tutorials/?noredirect=en_US#VT21

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