User manual

Table Of Contents
Appendix J
Underwater Inductive Modem (UIM)
Version 3.10 (and higher) of the MMP firmware supports real-time communication
between the MMP and a surface buoy, currently via a SeaBird inductive modem link (this
configuration option also requires a SeaBird inductive coupler). For the inductive modem
interface, the MMP electronics stack contains a SeaBird UIM (Underwater Inductive Modem)
board (SBE44 V1.8) with an inductive coupler around the mooring wire (a surface inductive
modem and surface controller are also required for this option).
This appendix describes the communications sequence between the MMP and the UIM.
A detailed description of SIM/UIM protocols are also provided.
Transmission Communication Sequence – Overview
Below is a process overview of the communication sequence between the Surface
Inductive Modem (SIM), the Underwater Inductive Modem (UIM) and the MMP. A complete
listing of file transmission protocols is provided on page J-7.
1. The sequence begins with the SIM powered off.
2. At the completion of a profile, the MMP powers on the UIM.
3. The UIM sends a tone detect to wake the SIM.
4. The MMP listens for commands transmitted by the SIM as the SIM performs a
Cyclic Redundancy Check (CRC) to ensure that data transmitted is valid. If the
CRC confirms valid data, the SIM sends the MMP a command to ‘send the next
piece of data’. If the CRC detects invalid data, the SIM sends the MMP a ‘resend
data’ command.
NOTE
The CRC calculated is a 16bit CCITT standard CRC.
5. The MMP sends a null record after the last group of data to tell the SIM that the
‘end of the data’ has been reached.
6. The MMP powers off the UIM and waits to perform the next profile.
Appendix J-
1