file: hullcom_ops.html
04 Nov 2002

HullCom/SST Sub-System Operations & Prep

See ASIMET MODULE OPERATIONS document for instructions on how to hook up the comms link to your PC and RS-485 adapter.
Refer to Latest Version Information for reference info on latest firmware version numbers.

Refer to HullCom/SST Commands for full command descriptions.

HullCom/SST Module System Description

The HullCom/SST "Module" is a system comprised of several interconnected devices which provides acquisition of Sea Surface Temperature data from a SeaBird SBE48 Hull-mounted Temperature Sensor via a pair of Harris Acoustic Products Acoustic Modems. From the user's perspective, operation is similar to most ASIMET Modules; standard ASIMET commands return various data and information from the module.

The HullCom/SST Module system normally consists of 3 units and associated cables and transducers. The master acoustic modem box contains the Harris modem board and its controller board, plus the HullCom/SST module controller board which provides the interface to the user described here. It connects via RS485 to the "outside world" - typically a larger Ship MET Data Logger system. This master modem box and transducer are placed on deck or someplace accessible by direct wire (RS485) from the Ship MET Data Logger. The slave acoustic modem box holds another Harris modem board and its controller board. This box and its transducer are typically placed deep in the ship, somewhere near the waterline. The 3rd unit is the SeaBird SBE48 Hull-mount Temperature sensor, which is mounted inside the ship's hull just below the waterline and connected via a short cable (RS232) to the slave acoustic modem box. Both the master and slave/SBE portions of the system are powered by local battery packs.

The HullCom/SST module firmware handles all the details of establishing the 20 baud acoustic modem link, waking up the SBE48 and getting the latest running average temperature (C command), then putting the modems to sleep for the next hour to save battery power. The SBE48 is typically set to internally log a running 60 minute average of sea surface temperature once every minute. This 1 minute data is only recoverable at the end of deployment by direct connection to the SBE48 (see the SeaBird SBE48 documentation). The HullCom/SST module system only grabs a sample (a one-hour average value at the moment) once per hour to limit battery consumption. The new sample is acquired at the rollover of the hour on the module internal clock (set by the D command).

On power-up, the HullCom/SST module checks its internal clock (RTC) and, if within the first 15 minutes of the hour, it will attempt to establish modem communications and acquire a new temperature. (After the first 15 minutes of the hour, a 0.000 temperature is reported until the top of the new hour when a new temperature is requested). Through the end of the current hour after power-up, the modems will NOT be put to sleep, allowing use of the T command. After the rollover to the next hour, a new temperature will be acquired, and the modems WILL be put to sleep for the duration of the hour. Note that in ideal conditions, the entire process of waking up the modems, acquiring a new temperature, and putting the modems to sleep takes only about one minute. For more info, see the T command.

Getting Started


The HullCom/SST sub-system (like ASIMET) has a communications protocol based on the SAIL (Serial ASCII Interface Loop) protocol developed at Oregon State University. The system is interrogated by sending commands with the following format (always with capital letters):


The L command, for example, will display several lines of status info about the instrument.

Once comms are established to the HullCom/SST controller, the system can be tested using the T command. This will test the complete HullCom/SST sub-system; if you get temperature back from the SBE48, the complete acoustic comms link and SBE48 are working. Read about the T command for a complete explanation. If the test fails, continue with direct testing of the Acoustic Modem controllers below.

Refer to HullCom/SST Commands for full command descriptions.

The HullCom/SST sub-system controller actually communicates with the master modem controller (as described above). By using an RS232 adapter cable and connecting a standard ASIMET power/comms cable to P1 on the ACMC530 master modem controller, it is possible to test the modems directly per the following description:


The Acoustic Modems require bi-directional communications when first powered up in order to set received data gain levels properly. Both modem controllers provide this by going into a "Training" mode at power-up or after a sleep interval.

"Training" involves sending an upper case "A" every six seconds until a "&&98" command is received by both master and slave modems (we generally assume that the master/upper unit sees the command properly the first time - see Troubleshooting below). During "Training", all characters are passed though as in normal operation but the automatic output or the "A" character continues.

After the "&&98" command is received, "Training" ends at each modem, and the modems pass all communications until a command is received.

Minimum Startup Communications

At a minimum, the user must stop the "Training" at both modems by sending the "&&98" command. If this command is properly received by the slave/lower unit, i.e. the modem attached to the Sea Surface Temperature (SBE48) module, it will respond with "98ADR". At this point the user knows there is proper communications with the lower modem and is free to send commands to the Sea Surface Temperature module.


It may take several attempts in sending the "&&98" command before the "98ADR" response is received from the lower unit. This may be due to timing. Since the acoustic link can communicate in only one direction at a time, if the lower unit sends an "A" while the upper unit is passing through the "&&98" command, the lower unit will not receive the command properly.

Also, if "A" characters are not being received from the lower modem after power-up, then proper communication with the upper modem controller can be tested, regardless of the "Training" status, with the "&&99" command. When the upper modem controller receives this command it responds with "99ADR". If the user receives this local acknowledgement but does not receive either periodic "A" characters or a response to the "&&98" command, then the acoustic link is broken and physical investigation is required.

REMEMBER that after any power cycle, the modem controllers go into the "Training" mode and must be dealt with accordingly.

RS232 to RS485 converters