Modbus reading some values wrong from the same device

[thedude911]

The problem

While reading some vaues correct, on the same device I have serious issues with one register. Holding Register 0012 and 0013 (uint32) contain the value 10700:

for no obvious reason, the number HA is receiving is 3 digits too large and also wrong:

What version of Home Assistant Core has the issue?

2025.6.1

What was the last working version of Home Assistant Core?

No response

What type of installation are you running?

Home Assistant OS

Integration causing the issue

Modbus

Link to integration documentation on our website

https://www.home-assistant.io/integrations/modbus/

Diagnostics information

home-assistant_modbus_2025-06-17T09-52-12.879Z.log

Example YAML snippet

modbus:                                                                                                   
  - name: wallbox                                                                                         
    type: tcp                                                                                             
    host: 192.168.0.22                                                                                    
    port: 502                                                                                             
    timeout: 60                                                                                           
    sensors:                                                                                              
      - name: wallbox.status                                                                              
        address: 0000                                                                                     
        data_type: uint16                                                                                 
        unique_id: wallbox_charging_station_state                                                         
      - name: wallbox.status.ladekabel                                                                    
        address: 0002                                                                                     
        data_type: uint16                                                                                 
        unique_id: wallbox_cable_state                                                                    
      - name: wallbox.fehlercode                                                                          
        address: 0004                                                                                     
        data_type: uint16                                                                                 
        unique_id: wallbox_fault_code                                                                     
      - name: wallbox.geladene.energie                                                                    
        unit_of_measurement: kWh                                                                          
        address: 0072                                                                                     
        data_type: uint16                                                                                 
        unique_id: wallbox_charged_energy                                                                 
        device_class: energy                                                                              
        state_class: total                                                                                
      - name: wallbox.ladedauer                                                                           
        unit_of_measurement: s                                                                            
        address: 0078                                                                                     
        data_type: uint32                                                                                 
        unique_id: wallbox_charging_time                                                                  
        device_class: duration                                                                            
        state_class: measurement                                                                          
      - name: wallbox.modus                                                                               
        address: 0093                                                                                     
        data_type: uint16                                                                                 
        unique_id: wallbox_charge_control                         
      - name: wallbox.ladeleistung.L1                                                                     
        unit_of_measurement: W                                                                            
        address: 0016                                                                                     
        data_type: uint32                                                                                 
        unique_id: wallbox_l1_charging_power                                                              
        device_class: power                                                                               
        state_class: measurement                                                                          
      - name: wallbox.ladeleistung.L2                                                                     
        unit_of_measurement: W                                                                            
        address: 0020                                                                                     
        data_type: uint32                                                                                 
        unique_id: wallbox_l2_active_power                                                                
        device_class: power                                                                               
        state_class: measurement                                                                          
      - name: wallbox.ladeleistung.L3                                                                     
        unit_of_measurement: W                                                                            
        address: 0024                                                                                     
        data_type: uint32                                                                                 
        unique_id: wallbox_l3_active_power                                                                
        device_class: power                                                                               
        state_class: measurement                                                                          
      - name: wallbox.ladeleistung                                                                        
        unit_of_measurement: W                                                                            
        address: 0012                                                                                     
        data_type: uint32                                                                                 
        unique_id: wallbox_active_power                                                                   
        device_class: power                                                                               
        state_class: measurement

Anything in the logs that might be useful for us?

Additional information

No response

[home-assistant]

modbus documentation
modbus source

[thedude911]

I solved the issue by removing the leading zeros from the register values, so e.g. 12 instead of 0012. Nevertheless, if the integration has an issue with how the values are defined, it needs to raise an error instead of behaving erradic.

[crug80]

I don't think the problem were the 0 before the register. It is an integer, so 00012 or 12 is the same for modbus and this can be easily verified checking the source code.

[Gnarfoz]

You'd think that, but... PyYAML for now only supports YAML 1.1, and in YAML 1.1, leading zeroes on numbers indicate... octal numbers!
So your 0012 was interpreted as 012 (octal) and was converted to decimal 10. So you got whatever was available at address 10 (possibly nothing valid, middle of a multi-byte register, who knows).

Some of the other sensors should be similarly affected:
wallbox.geladene.energie (72 -> 58)
wallbox.ladeleistung.L1 (16 -> 14)
wallbox.ladeleistung.L2 (20 -> 16)
wallbox.ladeleistung.L2 (24 -> 20)
Everything else is either below 8 (where octal = decimal) or uses digits illegal in octal (8, 9) and thus gets automatically interpreted as a decimal number.

YAML 1.2 introduces a 0o prefix, like the 0x prefix for hexadecimal numbers (0o173 = 0x7B = 123).

[crug80]

Thanks for the explanation @Gnarfoz . I checked the Modbus source code, but I didn't think the YAML parser could generate such a conversion!
Probably should we imporove the documentation to avoid possible errors?

[thedude911]

thank you @Gnarfoz, now this makes all perfectly sense. I also got 0 from register 16 and seemingly correct values from 20 and 24 (because all 3 are very similar in the value), which I could also not explain.

[Gnarfoz]

Regarding documentation, @crug80, I don't know - it's not an issue specific to Modbus, this could happen everywhere. It's more of a general YAML 1.1 pitfall.
Here's a short list: https://www.infoworld.com/article/2336307/7-yaml-gotchas-to-avoidand-how-to-avoid-them.html