Add support for local Modbus TCP

[SeBsZ]

So I discovered that in my MasterTherm installation I have access to instant local data via the Modbus TCP protocol. This is open and does not require and authentication or additional hardware.

Hardware Requirements

I have a MasterTherm geo heatpump installed in 2022 which came with a touchscreen display in the living area:

The screen used is by CAREL called pGDX (https://www.carel.com/pgdx). The screen connects to my WiFi and I can connect to its Modbus via TCP port 502.

Testing

To test if it works, download the free Open ModScan on Windows (https://github.com/sanny32/OpenModScan/releases) and go to Connection -> Connect. Choose 'Remote TCP/IP Server' and enter your Touchscreen's IP Address. Leave the port at 502 and click OK. Now leave the address and device id at 1. Choose 03: HOLDING REGISTER under 'MODBUS Point Type'. Make sure your data display option is set to integer:

It's working if you see data listed in the registers:

Home Assistant

To add this to Home Assistant, I suggest adding support for Modbus TCP to Masterthermconnect.

• There is no module ID or device ID
• There is no email/password needed

The MasterTherm integration would need to have its settings UI changed. All that's needed is the option to choose between 'MasterTherm Cloud' and 'Modbus TCP'. Then for Modbus users only need to enter an IP address.

Modbus has different types of registers you can read and sometimes write to:
0x = Coil = 00001-09999
1x = Discrete Input = 10001-19999
3x = Input Register = 30001-39999
4x = Holding Register = 40001-49999

We are only interested in the holding registers with address range 40001-49999. All the other registers are not used for this application.

Addresses

Since the first two address locations 40001 and 40002 are used for something else, everything is shifted by 2 when compared to our current implementation. Also, all the data types are one after the other.

Everything is stored as a signed integer.

Analog
A_1 -> 40003
A_2 -> 40004
A_500 -> 40502

All the above need to be divided by 10. For example a temperature of 17.1 is stored as 171.

Digital
D_1 -> 40503
D_2 -> 40504
D_496 -> 40998

Integers
I_1 -> 40999
I_2 -> 41000
I_500 -> 41498

I think the easiest is to use PyModbus. See Solaredge Modbus for an example implementation.

[sHedC]

Jealous, mine is locked with password and cert auth.

I will check this out as we discussed to try and make this easier I think map the numbers to the I_1 etc so I can map directly into and from the online mappings, then hopfully only need to replace the API part with a modbusAPI.

Do you think maybe login using the Web to get the setup then in options allow local connection and (hoping I find another way) have an option on type of connection for each device, once enabled it will switch the data updates to local for that specific device.

This probably doesn't matter for most people but just thinking if you have multiple devices to monitor (large houses), still that is a bit off have to get a connection which is going to be interesting as I can't test.

I think I will need you to share me sample data for Unit testing, once I work out how.

[sHedC]

This actually does work on mine to but in my case A_2 is 4002 and A_5 is 4006

[SeBsZ]

Oh really? You also have access to modbus TCP then?

[sHedC]

seems like it I pointed that app at it and it started updating, so need to work out if there really is a difference in where yours starts and where mine starts

[sHedC]

I changed the requested temp to 48.8 and it changed 4006 to 488, now the hot water is requesting 46.0 and its 460

[sHedC]

40038 and 40039 are A_37 and A_38 on mine

[sHedC]

Weird seems not to be mapped to the same as yours:

D_1 start at 1002 (02 - Input status)
A_1 start at 4002 (03 - Holding Register) also at (04 Input Register)
I_1 start at (No Idea)

[SeBsZ]

Well this is great news! This opens up local access to (nearly) everyone. We just need to allow for these different mapping types. Mine would be 'Carel pGDX' and yours would be whatever Gateway or Mastertherm you have. We'll have it selectable.

[sHedC]

yeh just knocked my pump offline :), but can still talk to it with pymodbus.

[SeBsZ]

Coils are 1-bit registers, read/write
Input status are 1-bit registers, read-only.
Input register are 16-bit registers, read-only
Holding register are 16-bit registers read/write

[SeBsZ]

Can you share a pic of your holding registers?