Problem reading Modbus RTU signals

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marcm
Posts: 8
Joined: 28 Jan 2025, 15:35

Problem reading Modbus RTU signals

Post by marcm »

Hello everyone,

I am creating this post because I am working with the RevPi Connect S and I am having some problems with the Modbus RTU.

I have been following the guides on your official tutorial website, your YouTube channel and also some guides you recommend in some of your forum replies about this topic. But I can't read the Modbus messages.

My status is the following:
- I have the Modbus RTU Master Gateway configured in Pictory according to our slave demands (9600 br; parity: none; 8 number bits, 1 stop bit).
- The device_path is correctly according to our physical setup: RS485
- I have 120 ohm terminal resistors.
- I have filled the "External data" of the Modbus RTU Master Gateway according to the datasheet of our slave device.
- I have used an oscilloscope between the RevPi Connect (Master) and the external device (salve) and I can certainly see some messages.
However, it is strange because I can't always see the message on the oscilloscope. Sometimes with a reboot I can still see the message, but at another time, without making any changes, after the reboot I am not able to see any message on the oscilloscope. As if there is an error or I have misunderstood it.
- When I try to debug in the SSH terminal, I can't see any message, I only read zeros when I use the following commands:
(when I ran these commands I was reading messages through the scope).

piTest -d

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Found 4 devices:

Address: 0 module type: 105 (0x69) RevPi Connect V1.0
Module is present
     input offset: 113 length: 6
    output offset: 119 length: 5

Address: 31 module type: 96 (0x60) RevPi DIO V1.5
Module is present
     input offset: 0 length: 70
    output offset: 70 length: 18

Address: 32 module type: 109 (0x6d) RevPi CON CAN V0.0
Module is present
     input offset: 0 length: 0
    output offset: 0 length: 0

Address: 64 module type: 24580 (0x6004) ModbusRTU Master Adapter V0.0
Module is present
     input offset: 124 length: 101
    output offset: 225 length: 73
piTest -r 124,101

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  0   0   0   0   0   0   0   0   0   0
  0   0   0   0   0   0   0   0   0   0
  0   0   0   0   0   0   0   0   0   0
  0   0   0   0   0   0   0   0   0   0
  0   0   0   0   0   0   0   0   0   0
  0   0   0   0   0   0   0   0   0   0
  0   0   0   0   0   0   0   0   0   0
  0   0   0   0   0   0   0   0   0   0
  0   0   0   0   0   0   0   0   0   0
  0   0   0   0   0   0   0   0   0   0
  0
piTest -r 225,73

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  0   0   0   0   0   0   0   0   0   0
  0   0   0   0   0   0   0   0   0   0
  0   0   0   0   0   0   0   0   0   0
  0   0   0   0   0   0   0   0   0   0
  0   0   0   0   0   0   0   0   0   0
  0   0   0   0   0   0   0   0   0   0
  0   0   0   0   0   0   0   0   0   0
  0   0   0   0   0   0   0   0   0   0
  0   0   0   0   0   0   0   0   0   0
  0   0   0   0   0   0   0   0   0   0
  0
piTest -r "device value name"

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2 Byte-Value of m11: 0 dez (=0000 hex)
2 Byte-Value of m11: 0 dez (=0000 hex)
2 Byte-Value of m11: 0 dez (=0000 hex)
2 Byte-Value of m11: 0 dez (=0000 hex)
sudo journalctl -u pimodbus-master.service (the code attached have a large number of lines because I was doing proves and rebooting the RevPi Connect S, and without do anything different and without I understand, it looks like sometimes the systems behave diferent.

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Feb 27 11:18:04 RevPi111847 piModbusMaster[2545]: piModbusMaster started
Feb 27 11:18:04 RevPi111847 piModbusMaster[2545]: piModbusMaster: ./src/piConfigParser/piConfigParser.c:1257: parse_modbus_master_action_list: Assertion `(q>
Feb 27 11:18:04 RevPi111847 systemd[1]: pimodbus-master.service: Main process exited, code=killed, status=6/ABRT
Feb 27 11:18:04 RevPi111847 systemd[1]: pimodbus-master.service: Failed with result 'signal'.
Feb 27 11:18:04 RevPi111847 systemd[1]: pimodbus-master.service: Scheduled restart job, restart counter is at 5.
Feb 27 11:18:04 RevPi111847 systemd[1]: Stopped Revolution Pi Modbus master.
Feb 27 11:18:04 RevPi111847 systemd[1]: pimodbus-master.service: Start request repeated too quickly.
Feb 27 11:18:04 RevPi111847 systemd[1]: pimodbus-master.service: Failed with result 'signal'.
Feb 27 11:18:04 RevPi111847 systemd[1]: Failed to start Revolution Pi Modbus master.
Feb 27 11:21:29 RevPi111847 systemd[1]: Started Revolution Pi Modbus master.
Feb 27 11:21:29 RevPi111847 piModbusMaster[3084]: piModbusMaster started
Feb 27 11:21:29 RevPi111847 piModbusMaster[3084]: RTU Master got serial device:/dev/ttyRS485
Feb 27 11:21:29 RevPi111847 piModbusMaster[3084]: modbus rtu action timeout: 0 s 500000 us
Feb 27 11:21:29 RevPi111847 piModbusMaster[3084]: modbus rtu minimal time between telegrams: 0 s 41666 us
Feb 27 11:22:52 RevPi111847 piModbusMaster[3084]: write to process image failed: -11
Feb 27 11:22:52 RevPi111847 piModbusMaster[3084]: read from process image failed: -11
Feb 27 11:22:52 RevPi111847 piModbusMaster[3084]: read from process image failed: -11
Feb 27 11:22:52 RevPi111847 piModbusMaster[3084]: read from process image failed: -11
Feb 27 11:22:52 RevPi111847 piModbusMaster[3084]: read from process image failed: -11
Feb 27 11:22:52 RevPi111847 piModbusMaster[3084]: read from process image failed: -11
Feb 27 11:22:52 RevPi111847 piModbusMaster[3084]: read from process image failed: -11
Feb 27 11:22:52 RevPi111847 piModbusMaster[3084]: read from process image failed: -11
Feb 27 11:22:52 RevPi111847 piModbusMaster[3084]: write to process image failed: -11
Feb 27 11:22:52 RevPi111847 piModbusMaster[3084]: read from process image failed: -11
Feb 27 11:22:52 RevPi111847 piModbusMaster[3084]: read from process image failed: -11
Feb 27 11:22:52 RevPi111847 piModbusMaster[3084]: read from process image failed: -11
Feb 27 11:22:52 RevPi111847 piModbusMaster[3084]: read from process image failed: -11
Feb 27 11:22:52 RevPi111847 piModbusMaster[3084]: read from process image failed: -11
Feb 27 11:22:52 RevPi111847 piModbusMaster[3084]: read from process image failed: -11
Feb 27 11:22:52 RevPi111847 piModbusMaster[3084]: read from process image failed: -11
Feb 27 11:22:53 RevPi111847 piModbusMaster[3084]: RTU Master got serial device:/dev/ttyRS485
Feb 27 11:22:53 RevPi111847 piModbusMaster[3084]: modbus rtu action timeout: 0 s 500000 us
Feb 27 11:22:53 RevPi111847 piModbusMaster[3084]: modbus rtu minimal time between telegrams: 0 s 41666 us
Feb 27 11:26:23 RevPi111847 piModbusMaster[3084]: RTU Master got serial device:/dev/ttyRS485
Feb 27 11:26:23 RevPi111847 piModbusMaster[3084]: modbus rtu action timeout: 0 s 500000 us
Feb 27 11:26:23 RevPi111847 piModbusMaster[3084]: modbus rtu minimal time between telegrams: 0 s 41666 us
Feb 27 11:30:54 RevPi111847 piModbusMaster[3084]: RTU Master got serial device:/dev/ttyRS485
Feb 27 11:30:54 RevPi111847 piModbusMaster[3084]: modbus rtu action timeout: 0 s 500000 us
Feb 27 11:30:54 RevPi111847 piModbusMaster[3084]: modbus rtu minimal time between telegrams: 0 s 41666 us
Feb 27 11:31:43 RevPi111847 piModbusMaster[3084]: RTU Master got serial device:/dev/ttyRS485
Feb 27 11:31:43 RevPi111847 piModbusMaster[3084]: modbus rtu action timeout: 0 s 500000 us
Feb 27 11:31:43 RevPi111847 piModbusMaster[3084]: modbus rtu minimal time between telegrams: 0 s 41666 us
Feb 27 11:32:26 RevPi111847 piModbusMaster[3084]: RTU Master got serial device:/dev/ttyRS485
Feb 27 11:32:26 RevPi111847 piModbusMaster[3084]: modbus rtu action timeout: 0 s 500000 us
Feb 27 11:32:26 RevPi111847 piModbusMaster[3084]: modbus rtu minimal time between telegrams: 0 s 41666 us
Feb 27 11:34:29 RevPi111847 systemd[1]: Stopping Revolution Pi Modbus master...
Feb 27 11:34:29 RevPi111847 systemd[1]: pimodbus-master.service: Succeeded.
Feb 27 11:34:29 RevPi111847 systemd[1]: Stopped Revolution Pi Modbus master.
-- Boot 927f78538e484a299c674d8f74f5390a --
Feb 27 11:35:01 RevPi111847 systemd[1]: Started Revolution Pi Modbus master.
Feb 27 11:35:01 RevPi111847 piModbusMaster[2474]: piModbusMaster started
Feb 27 11:35:01 RevPi111847 piModbusMaster[2474]: RTU Master got serial device:/dev/ttyRS485
Feb 27 11:35:01 RevPi111847 piModbusMaster[2474]: modbus rtu action timeout: 0 s 500000 us
Feb 27 11:35:01 RevPi111847 piModbusMaster[2474]: modbus rtu minimal time between telegrams: 0 s 41666 us
Feb 27 11:35:04 RevPi111847 piModbusMaster[2474]: modbus rtu action device: /dev/ttyRS485, slave address: 102 function: 0x04, address: 30071 failed -1/110/->
Feb 27 11:35:05 RevPi111847 piModbusMaster[2474]: modbus rtu action device: /dev/ttyRS485, slave address: 102 function: 0x03, address: 40015 failed -1/110/->
Feb 27 11:35:06 RevPi111847 piModbusMaster[2474]: modbus rtu action device: /dev/ttyRS485, slave address: 102 function: 0x04, address: 30071 failed -1/110/->
Feb 27 11:35:07 RevPi111847 piModbusMaster[2474]: modbus rtu action device: /dev/ttyRS485, slave address: 102 function: 0x03, address: 40015 failed -1/11/-1>
Feb 27 11:35:07 RevPi111847 piModbusMaster[2474]: read from process image failed: -11
Feb 27 11:35:07 RevPi111847 piModbusMaster[2474]: read from process image failed: -11
Feb 27 11:35:07 RevPi111847 piModbusMaster[2474]: read from process image failed: -11
Feb 27 11:35:07 RevPi111847 piModbusMaster[2474]: read from process image failed: -11
Feb 27 11:35:07 RevPi111847 piModbusMaster[2474]: read from process image failed: -11
Feb 27 11:35:07 RevPi111847 piModbusMaster[2474]: read from process image failed: -11
Feb 27 11:35:07 RevPi111847 piModbusMaster[2474]: read from process image failed: -11
Feb 27 11:35:07 RevPi111847 piModbusMaster[2474]: write to process image failed: -11
Feb 27 11:35:08 RevPi111847 piModbusMaster[2474]: read from process image failed: -11
Feb 27 11:35:08 RevPi111847 piModbusMaster[2474]: read from process image failed: -11
Feb 27 11:35:08 RevPi111847 piModbusMaster[2474]: read from process image failed: -11
Feb 27 11:35:08 RevPi111847 piModbusMaster[2474]: read from process image failed: -11
Feb 27 11:35:08 RevPi111847 piModbusMaster[2474]: read from process image failed: -11
Feb 27 11:35:08 RevPi111847 piModbusMaster[2474]: read from process image failed: -11
Feb 27 11:35:08 RevPi111847 piModbusMaster[2474]: read from process image failed: -11
Feb 27 11:35:08 RevPi111847 piModbusMaster[2474]: write to process image failed: -11
Feb 27 11:35:08 RevPi111847 piModbusMaster[2474]: read from process image failed: -11
Feb 27 11:35:08 RevPi111847 piModbusMaster[2474]: read from process image failed: -11
Feb 27 11:35:08 RevPi111847 piModbusMaster[2474]: read from process image failed: -11
Feb 27 11:35:08 RevPi111847 piModbusMaster[2474]: read from process image failed: -11
Feb 27 11:35:08 RevPi111847 piModbusMaster[2474]: read from process image failed: -11
Feb 27 11:35:08 RevPi111847 piModbusMaster[2474]: read from process image failed: -11
Feb 27 11:35:08 RevPi111847 piModbusMaster[2474]: read from process image failed: -11
Feb 27 11:35:08 RevPi111847 piModbusMaster[2474]: No modbus master configuration found in config file
Feb 27 11:49:14 RevPi111847 piModbusMaster[2474]: RTU Master got serial device:/dev/ttyRS485
Feb 27 11:49:14 RevPi111847 piModbusMaster[2474]: modbus rtu action timeout: 0 s 500000 us
Feb 27 11:49:14 RevPi111847 piModbusMaster[2474]: modbus rtu minimal time between telegrams: 0 s 41666 us
Feb 27 12:23:01 RevPi111847 piModbusMaster[2474]: RTU Master got serial device:/dev/ttyRS485
Feb 27 12:23:01 RevPi111847 piModbusMaster[2474]: modbus rtu action timeout: 0 s 500000 us
Feb 27 12:23:01 RevPi111847 piModbusMaster[2474]: modbus rtu minimal time between telegrams: 0 s 41666 us
Feb 27 12:27:00 RevPi111847 systemd[1]: Stopping Revolution Pi Modbus master...
Feb 27 12:27:00 RevPi111847 systemd[1]: pimodbus-master.service: Succeeded.
Feb 27 12:27:00 RevPi111847 systemd[1]: Stopped Revolution Pi Modbus master.
-- Boot ce2cbe39d84c4acfb2ae002a94eb71c9 --
Feb 27 12:27:32 RevPi111847 systemd[1]: Started Revolution Pi Modbus master.
Feb 27 12:27:32 RevPi111847 piModbusMaster[2499]: piModbusMaster started
Feb 27 12:27:32 RevPi111847 piModbusMaster[2499]: RTU Master got serial device:/dev/ttyRS485
Feb 27 12:27:32 RevPi111847 piModbusMaster[2499]: modbus rtu action timeout: 0 s 500000 us
Feb 27 12:27:32 RevPi111847 piModbusMaster[2499]: modbus rtu minimal time between telegrams: 0 s 41666 us
Feb 27 12:27:38 RevPi111847 piModbusMaster[2499]: write to process image failed: -11
Feb 27 12:27:38 RevPi111847 piModbusMaster[2499]: read from process image failed: -11
Feb 27 12:27:38 RevPi111847 piModbusMaster[2499]: read from process image failed: -11
Feb 27 12:27:38 RevPi111847 piModbusMaster[2499]: read from process image failed: -11
Feb 27 12:27:38 RevPi111847 piModbusMaster[2499]: read from process image failed: -11
Feb 27 12:27:38 RevPi111847 piModbusMaster[2499]: read from process image failed: -11
Feb 27 12:27:38 RevPi111847 piModbusMaster[2499]: read from process image failed: -11
Feb 27 12:27:38 RevPi111847 piModbusMaster[2499]: read from process image failed: -11
Feb 27 12:27:38 RevPi111847 piModbusMaster[2499]: write to process image failed: -11
Feb 27 12:27:38 RevPi111847 piModbusMaster[2499]: read from process image failed: -11
Feb 27 12:27:38 RevPi111847 piModbusMaster[2499]: read from process image failed: -11
Feb 27 12:27:38 RevPi111847 piModbusMaster[2499]: read from process image failed: -11
Feb 27 12:27:38 RevPi111847 piModbusMaster[2499]: read from process image failed: -11
Feb 27 12:27:38 RevPi111847 piModbusMaster[2499]: read from process image failed: -11
Feb 27 12:27:38 RevPi111847 piModbusMaster[2499]: read from process image failed: -11
Feb 27 12:27:38 RevPi111847 piModbusMaster[2499]: read from process image failed: -11
Feb 27 12:27:39 RevPi111847 piModbusMaster[2499]: write to process image failed: -11
Feb 27 12:27:39 RevPi111847 piModbusMaster[2499]: No modbus master configuration found in config file
Feb 27 12:28:26 RevPi111847 piModbusMaster[2499]: No modbus master configuration found in config file
Feb 27 12:28:59 RevPi111847 piModbusMaster[2499]: RTU Master got serial device:/dev/ttyRS485
Feb 27 12:28:59 RevPi111847 piModbusMaster[2499]: modbus rtu action timeout: 0 s 500000 us
Feb 27 12:28:59 RevPi111847 piModbusMaster[2499]: modbus rtu minimal time between telegrams: 0 s 41666 us
Feb 27 12:32:35 RevPi111847 systemd[1]: Stopping Revolution Pi Modbus master...
Feb 27 12:32:36 RevPi111847 systemd[1]: pimodbus-master.service: Succeeded.
Feb 27 12:32:36 RevPi111847 systemd[1]: Stopped Revolution Pi Modbus master.
-- Boot 5f22a2a5081243e0ab355019d51daee7 --
Feb 27 13:19:53 RevPi111847 systemd[1]: Started Revolution Pi Modbus master.
Feb 27 13:19:53 RevPi111847 piModbusMaster[2517]: piModbusMaster started
Feb 27 13:19:53 RevPi111847 piModbusMaster[2517]: RTU Master got serial device:/dev/ttyRS485
Feb 27 13:19:53 RevPi111847 piModbusMaster[2517]: modbus rtu action timeout: 0 s 500000 us
Feb 27 13:19:53 RevPi111847 piModbusMaster[2517]: modbus rtu minimal time between telegrams: 0 s 41666 us
Feb 27 13:20:00 RevPi111847 piModbusMaster[2517]: write to process image failed: -11
Feb 27 13:20:00 RevPi111847 piModbusMaster[2517]: read from process image failed: -11
Feb 27 13:20:00 RevPi111847 piModbusMaster[2517]: read from process image failed: -11
Feb 27 13:20:00 RevPi111847 piModbusMaster[2517]: read from process image failed: -11
Feb 27 13:20:00 RevPi111847 piModbusMaster[2517]: read from process image failed: -11
Feb 27 13:20:00 RevPi111847 piModbusMaster[2517]: read from process image failed: -11
Feb 27 13:20:00 RevPi111847 piModbusMaster[2517]: read from process image failed: -11
Feb 27 13:20:00 RevPi111847 piModbusMaster[2517]: read from process image failed: -11
Feb 27 13:20:00 RevPi111847 piModbusMaster[2517]: write to process image failed: -11
Feb 27 13:20:00 RevPi111847 piModbusMaster[2517]: read from process image failed: -11
Feb 27 13:20:00 RevPi111847 piModbusMaster[2517]: read from process image failed: -11
Feb 27 13:20:00 RevPi111847 piModbusMaster[2517]: read from process image failed: -11
Feb 27 13:20:00 RevPi111847 piModbusMaster[2517]: read from process image failed: -11
Feb 27 13:20:00 RevPi111847 piModbusMaster[2517]: read from process image failed: -11
Feb 27 13:20:00 RevPi111847 piModbusMaster[2517]: read from process image failed: -11
Feb 27 13:20:00 RevPi111847 piModbusMaster[2517]: read from process image failed: -11
Feb 27 13:20:00 RevPi111847 piModbusMaster[2517]: No modbus master configuration found in config file
Feb 27 13:22:12 RevPi111847 piModbusMaster[2517]: RTU Master got serial device:/dev/ttyRS485
Feb 27 13:22:12 RevPi111847 piModbusMaster[2517]: modbus rtu action timeout: 0 s 500000 us
Feb 27 13:22:12 RevPi111847 piModbusMaster[2517]: modbus rtu minimal time between telegrams: 0 s 41666 us
Feb 27 13:29:47 RevPi111847 systemd[1]: Stopping Revolution Pi Modbus master...
Feb 27 13:29:47 RevPi111847 systemd[1]: pimodbus-master.service: Succeeded.
Feb 27 13:29:47 RevPi111847 systemd[1]: Stopped Revolution Pi Modbus master.
-- Boot d6c5a37fe69d4e8690e90f245605cdad --
Feb 27 13:39:27 RevPi111847 systemd[1]: Started Revolution Pi Modbus master.
Feb 27 11:14:57 RevPi111847 systemd[1]: pimodbus-master.service: Main process exited, code=killed, status=6/ABRT
Feb 27 11:14:57 RevPi111847 systemd[1]: pimodbus-master.service: Failed with result 'signal'.
Feb 27 11:14:57 RevPi111847 systemd[1]: pimodbus-master.service: Scheduled restart job, restart counter is at 5.
Feb 27 11:14:57 RevPi111847 systemd[1]: Stopped Revolution Pi Modbus master.
Feb 27 11:14:57 RevPi111847 systemd[1]: Started Revolution Pi Modbus master.
Feb 27 11:14:57 RevPi111847 piModbusMaster[3088]: piModbusMaster started
Feb 27 11:14:57 RevPi111847 piModbusMaster[3088]: piModbusMaster: ./src/piConfigParser/piConfigParser.c:1257: parse_modbus_master_action_list: Assertion `(q>
Feb 27 11:14:57 RevPi111847 systemd[1]: pimodbus-master.service: Main process exited, code=killed, status=6/ABRT
Feb 27 11:14:57 RevPi111847 systemd[1]: pimodbus-master.service: Failed with result 'signal'.
Feb 27 11:14:57 RevPi111847 systemd[1]: pimodbus-master.service: Scheduled restart job, restart counter is at 6.
Feb 27 11:14:57 RevPi111847 systemd[1]: Stopped Revolution Pi Modbus master.
Feb 27 11:14:57 RevPi111847 systemd[1]: pimodbus-master.service: Start request repeated too quickly.
Feb 27 11:14:57 RevPi111847 systemd[1]: pimodbus-master.service: Failed with result 'signal'.
Feb 27 11:14:57 RevPi111847 systemd[1]: Failed to start Revolution Pi Modbus master.
-- Boot a4d41cf5f4b046dd93f61f061fe8a6da --
Feb 27 11:18:03 RevPi111847 systemd[1]: Started Revolution Pi Modbus master.
Feb 27 11:18:03 RevPi111847 piModbusMaster[2495]: piModbusMaster started
Feb 27 11:18:03 RevPi111847 piModbusMaster[2495]: piModbusMaster: ./src/piConfigParser/piConfigParser.c:1257: parse_modbus_master_action_list: Assertion `(q>
Feb 27 11:18:03 RevPi111847 systemd[1]: pimodbus-master.service: Main process exited, code=killed, status=6/ABRT
Feb 27 11:18:03 RevPi111847 systemd[1]: pimodbus-master.service: Failed with result 'signal'.
Feb 27 11:18:03 RevPi111847 systemd[1]: pimodbus-master.service: Scheduled restart job, restart counter is at 1.
Feb 27 11:18:03 RevPi111847 systemd[1]: Stopped Revolution Pi Modbus master.
I understand that the -11 problem means “0x11: Device does not respond or invalid register address”. But I have checked the slave address of my modbus slave device and it is the same address that I have configured in “Extended data” in my Modbus RTU Master virtual gateway in Pictory.

piTest -r Modbus_Action_Status_1

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1 Byte-Value of Modbus_Action_Status_1: 0 dez (=00 hex)
1 Byte-Value of Modbus_Action_Status_1: 0 dez (=00 hex)
1 Byte-Value of Modbus_Action_Status_1: 0 dez (=00 hex)
piTest -r Modbus_Master_Status

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1 Byte-Value of Modbus_Master_Status: 0 dez (=00 hex)
1 Byte-Value of Modbus_Master_Status: 0 dez (=00 hex)
1 Byte-Value of Modbus_Master_Status: 0 dez (=00 hex)
1 Byte-Value of Modbus_Master_Status: 0 dez (=00 hex)
Could you please help me understand what is wrong and what I could do to read the Modbus RTU messages?

Thank you very much for your help,

Best regards

Marc
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User avatar
dirk
Posts: 2271
Joined: 15 Dec 2016, 13:19

Re: Problem reading Modbus RTU signals

Post by dirk »

Hello Marc, thank you for your detailed description of the error. Which image are you using? Can you post the output from your system?

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pi@RevPi57688:~$ ls -la /dev/ttyRS485
lrwxrwxrwx 1 root root 7 Feb 27 15:50 /dev/ttyRS485 -> ttyUSB0
pi@RevPi57688:~$ cat /etc/revpi/image-release
250124-revpi-bookworm-arm64-default
pi@RevPi57688:~$ ^C
pi@RevPi57688:~$ apt list --installed pictory
Listing... Done
pictory/bookworm,now 2.11.1-1+deb12+1 all [installed,automatic]
N: There are 17 additional versions. Please use the '-a' switch to see them.
Apart from the information, here are some ideas that may lead to the goal:

Configure the Modbus RTU master in PiCtory without having the physical RS485 connection:
PiCtory Modbs RTU Master
PiCtory Modbs RTU Master
These types of errors should appear

Code: Select all

Feb 27 11:35:08 RevPi111847 piModbusMaster[2474]: read from process image failed: -11
Feb 27 11:35:08 RevPi111847 piModbusMaster[2474]: read from process image failed: -11
Feb 27 11:35:08 RevPi111847 piModbusMaster[2474]: read from process image failed: -11




pi@RevPi57688:~$ ls -la /dev/ttyRS485
lrwxrwxrwx 1 root root 7 Feb 27 15:50 /dev/ttyRS485 -> ttyUSB0
pi@RevPi57688:~$ sudo journalctl -u pimodbus-master.service
Mar 04 15:15:44 RevPi57688 systemd[1]: Started pimodbus-master.service - Revolution Pi Modbus master.
Mar 04 15:15:44 RevPi57688 piModbusMaster[4689]: piModbusMaster started
Mar 04 15:15:44 RevPi57688 piModbusMaster[4689]: Parsing config file failed: Action data object not found
Mar 04 15:15:44 RevPi57688 piModbusMaster[4689]: No modbus master configuration found in config file
Mar 04 15:16:05 RevPi57688 piModbusMaster[4689]: RTU Master got serial device:/dev/ttyRS485
Mar 04 15:16:05 RevPi57688 piModbusMaster[4689]: modbus rtu action timeout: 0 s 500000 us
Mar 04 15:16:05 RevPi57688 piModbusMaster[4689]: modbus rtu minimal time between telegrams: 0 s 250000 us
Mar 04 15:16:08 RevPi57688 piModbusMaster[4689]: modbus rtu action device: /dev/ttyRS485, slave address: 1 function: 0x04, address: 1 failed -1/110/-112345568
Mar 04 15:16:09 RevPi57688 piModbusMaster[4689]: modbus rtu action device: /dev/ttyRS485, slave address: 1 function: 0x04, address: 1 failed -1/110/-112345568
Mar 04 15:16:10 RevPi57688 piModbusMaster[4689]: modbus rtu action device: /dev/ttyRS485, slave address: 1 function: 0x04, address: 1 failed -1/110/-112345568
Mar 04 15:16:11 RevPi57688 piModbusMaster[4689]: modbus rtu action device: /dev/ttyRS485, slave address: 1 function: 0x04, address: 1 failed -1/110/-112345568
Mar 04 15:16:13 RevPi57688 piModbusMaster[4689]: modbus rtu action device: /dev/ttyRS485, slave address: 1 function: 0x04, address: 1 failed -1/110/-112345568
Solche Fehler sollten jedoch nicht auftreten:

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Feb 27 11:35:08 RevPi111847 piModbusMaster[2474]: read from process image failed: -11
Feb 27 11:35:08 RevPi111847 piModbusMaster[2474]: read from process image failed: -11
Feb 27 11:35:08 RevPi111847 piModbusMaster[2474]: read from process image failed: -11
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marcm
Posts: 8
Joined: 28 Jan 2025, 15:35

Re: Problem reading Modbus RTU signals

Post by marcm »

Hello Dirk,

Thank you very much for your reply and your advice.

ls -la /dev/ttyRS485

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lrwxrwxrwx 1 root root 7 Mar  4 11:58 /dev/ttyRS485 -> ttyUSB0
cat /etc/revpi/image-release

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2023-09-26-revpi-bullseye-armhf.img
apt list --installed pictory

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Listing... Done
pictory/bullseye,now 2.11.0-1+revpi11+1 all [installed]
N: There are 20 additional versions. Please use the '-a' switch to see them.
As you proposal, I have configured the Modbus RTU master in PiCtory without having the physical RS485 connection. And these are the results:
sudo journalctl -u pimodbus-master.service -n 15

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-- Journal begins at Sat 2023-05-13 10:36:59 UTC, ends at Thu 2025-03-06 08:02:39 UTC. --
Mar 06 07:58:31 RevPi111847 piModbusMaster[2471]: modbus rtu action device: /dev/ttyRS485, slave address: 101 function: 0x04, address: 30003 failed -1/110/-112345568
Mar 06 07:58:32 RevPi111847 piModbusMaster[2471]: modbus rtu action device: /dev/ttyRS485, slave address: 101 function: 0x04, address: 30001 failed -1/110/-112345568
Mar 06 07:58:33 RevPi111847 piModbusMaster[2471]: modbus rtu action device: /dev/ttyRS485, slave address: 101 function: 0x03, address: 40015 failed -1/110/-112345568
Mar 06 07:58:34 RevPi111847 piModbusMaster[2471]: modbus rtu action device: /dev/ttyRS485, slave address: 101 function: 0x03, address: 40025 failed -1/110/-112345568
Mar 06 07:58:35 RevPi111847 piModbusMaster[2471]: modbus rtu action device: /dev/ttyRS485, slave address: 101 function: 0x03, address: 40029 failed -1/11/-112345667
Mar 06 07:58:35 RevPi111847 piModbusMaster[2471]: read from process image failed: -11
Mar 06 07:58:35 RevPi111847 piModbusMaster[2471]: read from process image failed: -11
Mar 06 07:58:35 RevPi111847 piModbusMaster[2471]: read from process image failed: -11
Mar 06 07:58:35 RevPi111847 piModbusMaster[2471]: read from process image failed: -11
Mar 06 07:58:35 RevPi111847 piModbusMaster[2471]: read from process image failed: -11
Mar 06 07:58:35 RevPi111847 piModbusMaster[2471]: read from process image failed: -11
Mar 06 07:58:35 RevPi111847 piModbusMaster[2471]: read from process image failed: -11
Mar 06 07:58:35 RevPi111847 piModbusMaster[2471]: RTU Master got serial device:/dev/ttyRS485
Mar 06 07:58:35 RevPi111847 piModbusMaster[2471]: modbus rtu action timeout: 0 s 500000 us
Mar 06 07:58:35 RevPi111847 piModbusMaster[2471]: modbus rtu minimal time between telegrams: 0 s 41666 us

If these errors should not appear:

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Feb 27 11:35:08 RevPi111847 piModbusMaster[2474]: read from process image failed: -11
Feb 27 11:35:08 RevPi111847 piModbusMaster[2474]: read from process image failed: -11
What could be wrong?

Thank you very much for your help

Regards,

Marc
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User avatar
dirk
Posts: 2271
Joined: 15 Dec 2016, 13:19

Re: Problem reading Modbus RTU signals

Post by dirk »

Hello Marc,
thank you for your detailed report of the problem.
  • Can you share the Modbus configuration with us?
  • Furthermore, a Kern.log would be interesting to see if there are any further relevant error messages.
Alternatively, send us an SOS report. This gives us a comprehensive overview of your system, and works like this:
https://kunbus-gmbh.atlassian.net/servi ... CONFLUENCE

Edit: Take a look here where the -11 and other error codes here.



Thank you.
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