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Wireless M-BUS (wMbus) is a radio technology for meters and sensors that operates in 433 MHz and 868 MHz with short range of 30 to 150m (depending of environment).

Table of Contents

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RSSI

RSSI values are typically in the range von -60 dBm (good) to -107 dBm (bad)

Support of Lobaro Devices

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For parsing wMbus telegrams you can use our wMbus Parsing API

M-Bus Telegram Structure

Storage number

The storage number does group value by points in time.

There can be multiple value types inside a single storage number, typical values are:

Encryption

Wireless M-Bus Telegrams are usually encrypted  Image Added and must be decrypted Image Added  using a 16-Bit key.

When received by the Lobaro Plattform, you can configure decryption keys that are applied up on reception (see: wMbus Keys).

Telegram Coding

Telegram type A 

• Always for wMBUS S1 mode
• Always for wMBUS T1 mode
• Possible for wMBUS C1 mode
  • The detection is done via the syncword on phy level by the receiver

L-Field

The first byte of the first block is the length field. The field specifies the number of subsequent user bytes, including control and address bytes, but not CRC bytes. If ((L-9) MOD 16) is not zero, then the last block must contain ((L-9) MOD 16) data bytes +2 CRC bytes. All other blocks, except the first block, must always contain 16 data bytes + 2 CRC bytes.

CRCs

• First crc after 10 bytes
• Then every 16 bytes one CRC of length 2 (= 18)
• Plus one crc at the end (unless ending on 16 byte block)

Telegram type B

• Possible for wMBUS C1 mode
  • The detection is done via the syncword on phy level by the receiver

L-Field

The first byte of the first block is the length field. The field sets the number of all subsequent bytes, including all CRC bytes.

CRCs

The link layer check of telegram format B is performed on a maximum of 128 bytes, including the CRC field. Telegrams with a length of up to 128 bytes, including CRC and L field, contain a single CRC field covering both the first and the second block. Telegrams with a length between 131 bytes and 256 bytes (maximum length) contain two CRC fields, with the second CRC field covering the optional block. 

JS wMbus Parser

Compatible Parser for the Lobaro Platform, TTN / TTI and Chirpstack.

//////////////////////
// Helper
//////////////////////

// Convert a hex string to a byte array
function hexToBytes(hex) {
    for (var bytes = [], c = 0; c < hex.length; c += 2)
        bytes.push(parseInt(hex.substr(c, 2), 16));
    return bytes;
}

// Convert a byte array to a hex string
function bytesToHex(bytes) {
    for (var hex = [], i = 0; i < bytes.length; i++) {
        var current = bytes[i] < 0 ? bytes[i] + 256 : bytes[i];
        hex.push((current >>> 4).toString(16));
        hex.push((current & 0xF).toString(16));
    }
    return hex.join("");
}

// MFieldToString is Calculated from MField (15 bit) and represented as 3 ASCII chars
// First bit is ignored and used to define the uniqueness of the Meter Id
// AAA = 0x0421 = 0 00001 00001 00001
// ZZZ = 0x6b5a = 0 11010 11010 11010
function MFieldToString(m) {
    var letters = ""
    var char3 = (m&0x1F)+64
    var char2 = ((m&0x3E0) >> 5)+64
    var char1 = ((m&0x7C00) >> 10)+64
    letters += String.fromCharCode(char1)
    letters += String.fromCharCode(char2)
    letters += String.fromCharCode(char3)
    return letters
}


// ParseWmbus returns a struct with the wMbus telegram header information plus the raw telegram
// telegram is the whole telegram as byte slice (each element of the slice contains one byte value as number)
//
// Data Link Layer:
// ----------------
//   0  |   1  |  2   |   3  |  4   |   5  |   6  |   7  |   8  |   9    |  10  |  11  | -> Application Layer
// 0x2E | 0x44 | 0xB0 | 0x5C | 0x12 | 0x13 | 0x00 | 0x00 | 0x02 | 0x1B   | 0x8A |  ... |
// Len  |  C   |  M   |  M   |   ID |  ID  |  ID  |  ID  | Ver  | Device |  CRC |  CRC |
function ParseWmbus(telegram) {
    var id = bytesToHex(telegram.slice(4, 8).reverse());
    var mField = MFieldToString((telegram[2] << 0) + (telegram[3] << 8));
    var version = telegram[8];
    var deviceType = telegram[9];

    return {
        "Id": id,
        "MField": mField,
        "Version": version,
        "Device": deviceType,
        "Telegram": bytesToHex(telegram)
    }
}