Zephyr MODBUS samples

Question

Hi 
 We wan't use in our project some MODBUS sensors and I found, that Nordic Connect SDK (I use version 1.9.1) with Zephyr has support for MODBUS. I tried the samples (rtu- server and rtu-client), but I don't get them work. They compile OK and if I look with logic analyzer, client is asking and the server is answering with right data and frames, but client shows always: 
 
 Everything is connected as it should (server is answering). Has anyone tried the MODBUS samples and get them to work? 
 
 I add also logic analyzer images: 
 That is the client asking 
 
 And server answers: 
 
 Tiit

dejans · Accepted Answer

Hi Tiit, 
 Tiit said: Do you use also RS232 for communication? I have tested the example first -- I didn't touch the settings (only commented DE pin out, because I don't use RS485 tranceiver) and connected Arduino serial (UART1, RX - 1.01, TX - 1.02) pins crossed between two boards -- I see only RX timed out. 
 I connected two boards the same way, with pins P1.01 and P1.02 on one board connected to the pins P1.02 and P1.01 on the second board, respectively. I did not use RS485 and I was observing communication on the boards' COM ports. 
 Tiit said: It's strange, because the server board is recieving coil change messages (log shows, but LED-s stay off). 
 The client board is sending MODBUS messages and server board is answering (as I see from logic analyzer), but client board shows only the RX timeout error. 
 I could see "Coils state change" on the client side, and "Coil write" and "Coil read" on the server side. Best regards, Dejan

Tiit · Answer

Hi Dejan 
 
 I got it working, but I don't know what was the problem actually. I removed everything releated to SDK, cleaned the folders and reinstalled from scratch and the example worked straight out of the box. That is strange, because it was not working with 1.8.0, 1.9.0 and also with 1.9.1 -- i tried different SDK versions more than one time. 
 I got my sensor also working -- Senseair Sunrise uses non-standard approach for MODBUS checksum stopbits and I modified SDK-s Zephyr MODBUS subsystem files with a patch, that is included in newer Zephyr version ( modbus: stop bits can now be set individually by Constikri &middot; Pull Request #40558 &middot; zephyrproject-rtos/zephyr &middot; GitHub ). 
 
 Tiit

Zephyr MODBUS samples

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