Modbus not setting/reading value with error "Very short frame (NO MBAP)"

Configuration
,
1

Hello together,

I’m setting up a fully Modbus controlled HVAC system in Germany (getting a little hot in here). Using oModbusMaster I can set and read holding registers over my setup successfully.

Here it is:

  • 5x Futjitsu UTY-VMSX
  • 1x WaveShare DIN-Rail RS485 to ETH gateway

I have configured the gateway to conduct the RTU to Modbus-TCP conversion and happily am using it from my Mac Modbus client that way (checked for framing issues).

Sadly with my homeassistant config it does not work
I am looking for hints to further debug it!

Here is my minimal config to check I can control one register first:

- name: "waveshare"
  type: tcp
  host: 172.16.1.59
  port: 502
  delay: 10
  switches:
    - name: "wozi_power"
      unique_id: "modbus_wozi_power"
      slave: 1
      address: 3
      command_on: 2
      command_off: 1
      verify:
    - name: "schlafz_power"
      unique_id: "modbus_schlafz_power"
      slave: 2
      address: 3
      command_on: 2
      command_off: 1
      verify:

This means my HVAC is set to on with a value of 2 and off with a value of 1.

Here is what I get from debug logging when flipping the Switch under entities in the GUI:

2024-11-10 08:15:21.047 DEBUG (MainThread) [pymodbus.logging] Adding transaction 111
2024-11-10 08:15:21.047 DEBUG (MainThread) [pymodbus.logging] Resetting frame - Current Frame in buffer -
2024-11-10 08:15:21.047 DEBUG (MainThread) [pymodbus.logging] send: 0x0 0x6f 0x0 0x0 0x0 0x6 0x1 0x6 0x0 0x3 0x0 0x2
2024-11-10 08:15:21.084 DEBUG (MainThread) [pymodbus.logging] recv: 0x0 0x6f 0x0 0x0 0x0 0x6 0x1 0x6 0x0 0x3 0x0 0x2 old_data:  addr=None
2024-11-10 08:15:21.085 DEBUG (MainThread) [pymodbus.logging] Processing: 0x0 0x6f 0x0 0x0 0x0 0x6 0x1 0x6 0x0 0x3 0x0 0x2
2024-11-10 08:15:21.085 DEBUG (MainThread) [pymodbus.logging] Factory Response[WriteSingleRegisterResponse': 6]
2024-11-10 08:15:21.085 DEBUG (MainThread) [pymodbus.logging] Getting transaction 111
2024-11-10 08:15:21.085 DEBUG (MainThread) [pymodbus.logging] Very short frame (NO MBAP):  wait for more data
2024-11-10 08:15:21.085 DEBUG (MainThread) [pymodbus.logging] Adding transaction 112
2024-11-10 08:15:21.085 DEBUG (MainThread) [pymodbus.logging] Resetting frame - Current Frame in buffer -
2024-11-10 08:15:21.086 DEBUG (MainThread) [pymodbus.logging] send: 0x0 0x70 0x0 0x0 0x0 0x6 0x1 0x3 0x0 0x3 0x0 0x1
2024-11-10 08:15:21.087 DEBUG (MainThread) [pymodbus.logging] recv: 0x0 0x70 0x0 0x0 0x0 0x5 0x1 0x3 0x2 0x0 0x2 old_data:  addr=None
2024-11-10 08:15:21.087 DEBUG (MainThread) [pymodbus.logging] Processing: 0x0 0x70 0x0 0x0 0x0 0x5 0x1 0x3 0x2 0x0 0x2
2024-11-10 08:15:21.087 DEBUG (MainThread) [pymodbus.logging] Factory Response[ReadHoldingRegistersResponse': 3]
2024-11-10 08:15:21.087 DEBUG (MainThread) [pymodbus.logging] Getting transaction 112
**2024-11-10 08:15:21.087 DEBUG (MainThread) [pymodbus.logging] Very short frame (NO MBAP):  wait for more data**

I seem to read from this log that HA is sending the required 2 to the gateway and receives confirmation. However, the HVAC with slave 1 is not turned on and does not switch the holding register 40003 to 2.

Is there any debugging you can recommend to me?

Best

2

So this is really related to the strict implementation of Modbus specifications in Homeassistant.

For the UTY-VMSX you must subtract 1 (one) from each given register address to reach the right register.

To make this pretty clear for myself and the worlds in ten years:

Reading from holding register named 40003 in the documentation (Betriebs-EIN/AUS-Einstellung), the address 2 must be used. Reading/writing holding registers is the default.

Reading from input register 30054 in the documentation (Betriebs-EIN/AUS-Status), the address 53 and the input_type: input must be used.

Here is a working minimal config to build upon:

- type: tcp
  host: 172.16.1.59
  port: 502
  switches:
    - name: "wozi_power"
      unique_id: "modbus_wozi_power"
      slave: 1
      address: 2
      command_on: 2
      command_off: 1
      verify:
  sensors:
    - name: "wozi_status_mode"
      unique_id: "modbus_wozi_status_mode"
      slave: 1
      address: 53
      input_type: input
    - name: "wozi_status_power"
      unique_id: "modbus_wozu_status_power"
      slave: 1
      address: 54
      input_type: input
    - name: "wozi_target_temperature"
      unique_id: "modbus_wozi_target_temperature"
      slave: 1
      address: 55
      input_type: input
      scale: 0.25
      precision: 1
      unit_of_measurement: "C"