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myCNC - advanced CNC control, software - How to diagnose Modbus communication

Frequently Asked Question

How to diagnose Modbus communication

myCNC Ethernet controllers contain RS485 bus connector with RTU-modbus and ASCII-modbus implemented protocols.

Modbus can be configured through configuration tab "Technology"->"Spindle"


1) Check "RS 485/Modbus communication" to enable RS485/Modbus on myCNC Ethernet controller.
2) Setup "RS485" comminication speed according your inverter settings.
3) Setup "Inverter Address" and check the first checkbox.
address value 0...15 are reserved in myCNC or non-modbus devices, Modbus Inverter address value should be 16 or more;
For 1-spindle configuration the first checkbox only should be checked. Other checkboxes are for multi-spindle configurations.

 4) Modbus diagnostic mode.

If "Spindle" Tab dialog is open, myCNC software can ping over Modbus selected registers for testing pupose. If register selected, myCNC tries to read them 2 times per second.
myCNC shows register value if reply recieved.
If inverter replies with exception myCNC shows register address that generates exception.

On a picture below there are 2 registers choosen for ping: #2239, #8192

A- Register #2239 value is received and shown ("1")

B- Inverter replied with Exception regarding register #8192


 If "modbus diagnose" checkbox is checked, myCNC shows all traffic between myCNC controller and modbus device (Inverter).

 Blue lines are outgoing traffic from myCNC Etherent controller to Modbus unit. There are extra ">" symbol and current time added to each line. Red lines are modbus unit (Inverter) reply. On a pictures below examples of Modbus traffic.

1- No income traffic (Modbus unit is disconnected or configured not properly

2- Correct traffic between Modbus client (myCNC contrller) and Modbus server (Inverter)