> For the complete documentation index, see [llms.txt](https://help.aranet.com/llms.txt). Markdown versions of documentation pages are available by appending `.md` to page URLs; this page is available as [Markdown](https://help.aranet.com/base-stations/base-stations/integrations-and-3rd-party-systems/modbus/requesting-data-from-aranet-pro-modbus-tcp-ip-server.md).

# Requesting data from Aranet PRO Modbus TCP/IP server

Important notes for the client side:

| Parameter            | Value                                                                                              |
| -------------------- | -------------------------------------------------------------------------------------------------- |
| Register size        | 16 bits                                                                                            |
| Unit ID (slave ID)   | 1 (not changeable)                                                                                 |
| Supported functions  | Read discrete inputs (code: 2), read input registers (code: 4)                                     |
| Supported data types | Discrete inputs, input registers (any address in the supported range of 0—65535)                   |
| Endianness           | Big-endian with high word first (high byte first or high word first for 2 registers/32-bit values) |

### Used Modbus TCP exceptions

* Unsupported function requested → ILLEGAL\_FUNCTION.
* Unavailable registry address requested → ILLEGAL\_DATA\_ADDRESS. This exception is also sent if a particular address is colliding with any other registry address.
* Uninitialized registry address requested → ILLEGAL\_DATA\_VALUE. The address exists, but valid data of measurement has not been assigned yet.

### Custom address-to-measurements mapping: Input registers

Below is an example of an uploaded custom address-to-measurements mapping configuration JSON file used for input registers (example with three 2×16-bit wide registries):

```json
{ 
  "inputRegisters": {
    "1056849": {
      "battCharge": { // Registry address: 30044
        "dataType": "int32",
        "multiplier": 100,
        "offset": 4
      },
      "offset": 40,
      "rssi": { // Registry address: 30046
        "dataType": "int32",
        "multiplier": 1,
        "offset": 6
      },
      "time": { // Registry address: 30048
        "dataType": "uint32",
        "multiplier": 1,
        "offset": 8
      }
    },
    "offset": 30000
  }
}
```

Representation in a Modbus client application is shown in Fig. 3.

<figure><img src="/files/wsbzRPTAXmgGcTUhX2xF" alt=""><figcaption></figcaption></figure>

<p align="center">Figure 3: Modbus client application view with an example configuration</p>

### Custom address-to-measurements mapping: Discrete inputs

Example of uploaded custom mapping configuration for Discrete inputs:

```json
"discreteInputs": {
  "4196581": {
    "offset": 20,
    "rssiAlarm": { // Registry address: 10020
      "dataType": "bit",
      "multiplier": 1,
      "offset": 1
    }
  },
  "6292285": {
    "offset": 20,
    "rssiAlarm": { // Registry address: 10021
      "dataType": "bit",
      "multiplier": 1,
      "offset": 0
    }
  },
  "offset": 10000
}
```

<figure><img src="/files/fIcuano27gA0AYsl867a" alt=""><figcaption></figcaption></figure>

<p align="center">Figure 4: Modbus client application view with an example configuration</p>


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