.. _headlabel-refx-data-81:

Data 81 (Mini Location)
=======================

The mini location information, only provides 6 parts information of fix state, fix mode, longitude, latitude, UTC time and speed.

The frame format of the Data **81** unit is as follows:

.. code-block:: none

   For example (Total 17 bytes):
   51 0F 09 07 3C 46 FF 01 DB 88 57 5F 17 9D A0 01 7D

.. tabularcolumns:: |p{3.2em}|p{12.2em}|p{5.8em}|p{13em}|p{4.8em}|

.. table::
   :width: 100%
   :widths: auto

   +---------+---------------------------------------------+---------------+--------------------------------------------+--------------+
   | Parts   | Fields                                      | Length (Byte) | Range/Format                               | Default      |
   +=========+=============================================+===============+============================================+==============+
   | ID      | Data ID                                     | 1             | 51H (81)                                   | 51H (81)     |
   +---------+---------------------------------------------+---------------+--------------------------------------------+--------------+
   | Length  | Data Length                                 | 1             | 00H or 0FH                                 |              |
   +---------+---------------------------------------------+---------------+--------------------------------------------+--------------+
   | Content | `Fix State & Fix Mode`                      | 1             |                                            |              |
   +         +---------------------------------------------+---------------+--------------------------------------------+--------------+
   |         | `Longitude`                                 | 4             |                                            |              |
   +         +---------------------------------------------+---------------+--------------------------------------------+--------------+
   |         | `Latitude`                                  | 4             |                                            |              |
   +         +---------------------------------------------+---------------+--------------------------------------------+--------------+
   |         | `UTC Time`                                  | 4             |                                            |              |
   +         +---------------------------------------------+---------------+--------------------------------------------+--------------+
   |         | `Speed`                                     | 2             | 0000H-FFFFH (\*0.1 km/h)                   |              |
   +---------+---------------------------------------------+---------------+--------------------------------------------+--------------+

- `Fix State & Fix Mode`

  The upper 4 bits (bit7 to bit4) represent satellites signal strength level, the next 2 bits (bit3 to bit2) represent the fix state, and the lowest 2 bits (bit1 to bit0) represent the fix mode. Details are as follows.

  - **Signal Strength Level** (Bit7 to Bit4)

    Indicates the signal strength level of the satellites in use.

    - **0b0000** - Unknown.

    - **0b0001** - Great.

    - **0b0010** - Good.

    - **0b0011** - Normal.

    - **0b0100** - Weak.

    Typical values are as follows:

    +-------------+------------------------------+-----------+
    | Value       | Signal Strength (C/N0)       | Level     |
    +=============+==============================+===========+
    | 0           | Unknown                      | Unknown   |
    +-------------+------------------------------+-----------+
    | 1           | C/N0 >= 40                   | Great     |
    +-------------+------------------------------+-----------+
    | 2           | 33 <= C/N0 < 40              | Good      |
    +-------------+------------------------------+-----------+
    | 3           | 28 <= C/N0 < 33              | Normal    |
    +-------------+------------------------------+-----------+
    | 4           | C/N0 < 28                    | Weak      |
    +-------------+------------------------------+-----------+

  - **Fix State** (Bit3 to Bit2)

    Indicates the current positioning status of the GNSS chip.

    - **0b00** - Off. GNSS is not working at the moment. In this case, the 'longitude', 'latitude', 'speed', 'UTC time' etc. are the same as the last valid positioning.

    - **0b01** - No fix. GNSS worked but could not get the position. In this case, the 'longitude', 'latitude', 'speed', 'UTC time' etc. are the same as the last valid positioning.

    - **0b10** - Fix. GNSS worked and got the accurate location. The values of all fields are reliable to use.

  - **Fix Mode** (Bit1 to Bit0)

    Indicates in which positioning mode the following position information (longitude, latitude, etc.) was obtained.

    - **0b00** - 2D GNSS fix.

    - **0b01** - 3D GNSS fix.

    - **0b11** - Unknown.

- `Longitude`

  The longitude is converted to an integer with 6 implicit decimals and this integer is reported in HEX format; if its value is negative, it is represented in 2's complement format. For the converted longitude, a positive number indicates the east longitude and a negative number indicates the west longitude.

  For example, 073C46FFH (i.e., 121390847) means longitude 121.390847 degrees, and F920A8E1H (i.e., -115300127) means longitude -115.300127 degrees.

- `Latitude`

  The latitude is converted to an integer with 6 implicit decimals and this integer is reported in HEX format; if its value is negative, it is represented in 2's complement format. For the converted latitude, a positive number indicates the north latitude and a negative number indicates the south latitude.

  For example, 01DB8857H (i.e., 31164503) means latitude 31.164503 degrees, and FF2DC096H (i.e., -13778794) means latitude -13.778794 degrees.

- `UTC Time`

  The UTC time obtained from the GNSS chip, difference, in seconds, between the current time and midnight, January 1, 1970.

  For example, 5DD52EFAH (i.e., 1574252282) means November 20, 2019, 20:18:02.

- `Speed`

  The speed is obtained from the GNSS chip. Speed over ground, expressed as a 16-bit unsigned integer and the unit is 0.1 km/h.

  For example, 017DH (i.e., 381) means speed 38.1 km/h.