Specifications

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5.7.2 Datawell message format
As any message-type format the Datawell message format brings about a high degree of
flexibility. In addition, the Datawell message format incorporates two compression methods:
• transformation of real numbers to integers, and
• smart decimation
As a result also compact messages for low-capacity, high-cost datalinks such as satellite
communication are possible. This subsection starts with the format, listing and discussion of the
currently defined messages. After that the abovementioned compression methods are explained.
5.7.2.1 Message format and defined messages
Table 5.7.8 describes the general format for the first 15 messages.
Table 5.7.8. Format of the first 15 messages
Byte HiNibble LoNibble
0 MsgID (0..9A..E) CRC-4 checksum
1 Data
2 Data
… …
n-1 Data
For the next 256 messages, the format is described in Table 5.7.9.
Table 5.7.9. Format of the 256 messages
following the first 15.
Byte HiNibble LoNibble
0 Header (F = 1111) CRC-4 checksum
1 MsgID
(00..FF)
2 Data
… …
n-1 Data
The calculation of the CRC-4 checksum is explained in the next subsubsection.
Until now, five messages have been defined, see Table 5.7.10. Keeping in mind the due
long Argos ID’s, which leaves only 31 bytes for the message body, the size of several messages
is limited to 31 bytes. Note that also the combination of messages 3, 5 and 6 totals 31 bytes.
In the future, new message formats can be added within the present scheme.
Table 5.7.10. Overview of currently defined messages.
MsgID Message Message length
(bytes)
0 Compressed heave spectrum 31
3 Spectral parameters 11
5 Buoy information (“System file”) 10
6 Meteorological parameters 10
9 Compressed directional spectrum 31
F
(subindexing)
-