2.3. Selected intention (BDS 4,0)

In BDS 4,0, information such as aircraft selected altitude and barometric pressure settings are given. The 56-bit MB field is structured as follows:

+---------------------------------------+------+------+
| FIELD                                 | MB   |N-BITS|
+=======================================+======+======+
| Status                                |  1   |  1   |
+---------------------------------------+------+------+
| MCP/FCU selected altitude             |  2   |  12  |   **
|                                       |      |      |
| range = [0, 65520] ft                 |      |      |
|                                       |      |      |
| LSB: 16 ft                            |  13  |      |
+---------------------------------------+------+------+
| Status                                |  14  |  1   |
+---------------------------------------+------+------+
| FMS selected altitude                 |  15  |  12  |   **
|                                       |      |      |
| range = [0, 65520] ft                 |      |      |
|                                       |      |      |
| LSB: 16 ft                            |  26  |      |
+---------------------------------------+------+------+
| Status                                |  27  |  1   |
+---------------------------------------+------+------+
| Barometric pressure setting           |  28  |  12  |   **
|   -> Note: actual value minus 800     |      |      |
|                                       |      |      |
| range = [0, 410] mb                   |      |      |
|                                       |      |      |
| LSB: 0.1 mb                           |  39  |      |
+---------------------------------------+------+------+
| Reserved                              |  40  |  8   |
|   -> set to ZEROS                     |      |      |
|                                       |  47  |      |
+---------------------------------------+------+------+
| Status                                |  48  |  1   |
|   -> next 3 fields                    |      |      |
+---------------------------------------+------+------+
| Mode: VNAV                            |  49  |  1   |
+---------------------------------------+------+------+
| Mode: Alt hold                        |  50  |  1   |
+---------------------------------------+------+------+
| Mode: Approach                        |  51  |  1   |
+---------------------------------------+------+------+
| Reserved                              |  52  |  2   |
|   -> set to ZEROS                     |  53  |      |
+---------------------------------------+------+------+
| Status                                |  54  |  1   |
+---------------------------------------+------+------+
| Target alt source                     |  55  |  2   |
|   -> 00: Unknown                      |      |      |
|   -> 01: Aircraft altitude            |      |      |
|   -> 10: FCU/MCP selected altitude    |      |      |
|   -> 11: FMS selected altitude        |  56  |      |
+---------------------------------------+------+------+

An example:

MSG:  A000029C85E42F313000007047D3
MB:           85E42F31300000

---------------------------------------------------------------------------------
MB BIN:   1 000010111100 1 000010111100 1 100010011000 00000000 0 0 0 0 00 0 00
---------------------------------------------------------------------------------
STATUS:   1
MCP:        188 (x16)
---------------------------------------------------------------------------------
STATUS:                  1
FMS:                       188 (x16)
---------------------------------------------------------------------------------
STATUS:                                 1
BARO:                                     2200 (x0.1 + 800)
---------------------------------------------------------------------------------
FINAL:      3008 ft        3008 ft        1020 mb
---------------------------------------------------------------------------------