Rheonics Support

1.MODBUS RTU TROUBLESHOOTING

1.1.Verify the Baud Rate, Stop Bits, Data Bits and Parity.

Factory default settings of Modbus parameters:

address=1

baudrate=38400

parity=odd

Figure 1. Troubleshooting serial settings

1.2. Check reversed polarity on rs485 lines, swap wire A and B.

Figure 2. Troubleshooting reverse polarity

1.3. Slave Address: With RS485 RTU you can daisy chain up to 32 Slave devices (don’t forget termination). For Modbus RTU Master, make sure that all Slave device addresses match what the master is trying to connect to. The slave address can be set in the RCP in the “Communication” Tab.

Figure 3. Troubleshooting slave address.

1.4.  Make sure the biasing resistors and termination resistors and proper setup for the RS485 network is installed.

Figure 4. Troubleshooting network topology

1.5. Check that slave device is enabled for Modbus communication, this must be done by our Rheonics agent. (https://support.rheonics.com/support/solutions/articles/81000390438-updating-sensor-configuration). 

1.6. Use the speed that is necessary for the application, the following picture is a good reference to select the speed, this will help in having a more efficient communication. 

Figure 5. Troubleshooting speed 

1.7. Routing cables for communication with power cables, the best option for communication wires is to use Shielded & twisted pair RS485 cable is always recommended

2. CRC ERRORS

It usually means that the device is at least recognizing bit activity on the network line, however the bits probably make no sense to the device. If getting these errors check the following:

•    Check baud rate and character format.

•    Check wiring – if everything else is correct, CRC errors mean noise on the line.

•    Check for reversed polarity on RS485 lines. Reversed polarity often looks like just noise.

•    Check to see that Pre-Delay is at least 50 mS.

3. MODBUS DEBUGGING TOOLS

Modbus Poll is a Modbus master simulator designed primarily to help developers of Modbus slave devices or others that want to test and simulate the Modbus protocol. 

https://www.dropbox.com/sh/lv76vwm5lnpy79b/AACL7dhgIydyX_QcV7GK5Ir1a?dl=0