User manual

during every hour of operation. When the TT8v2 receives this interrupt, the TT8v2
acknowledges and clears the request by communicating with the DS1306. Then the TT8v2 resets
the 68 minute counter to zero, logs the IRQ if a deployment is in progress, and goes on with
whatever operation was being conducted when the interrupt was received. These actions indicate
the TT8v2 is smoothly running the firmware. As long as the TT8Vv2 is operating properly, the
counter never rolls over and the TT8V2 is never rebooted.
URAO Operation
In the (unlikely) event of a processor crash, the watchdog circuit triggers the Unattended
Reset, Autonomous Operation (URAO) feature of the firmware. URAO autonomously resets the
system, loads the correct time from the DS1306, recovers the deployment parameters
programmed by the operator, and restarts the deployment already in progress. URAO also
functions in the event of a transient loss of the main power supply. URAO is described in more
detail in Chapter 7, “User Interface”.
If the TT8v2 crashes, it is no longer running the firmware or has been put to sleep by the
critical handler after a detectable fault. The watchdog continues to operate autonomously and
sends a scheduled IRQ to the TT8v2. The unresponsive TT8v2 ignores the interrupt and, in
consequence, the counter, which has counted 60 minutes of its 68 minute period, is not reset.
Approximately eight minutes later the counter rolls over and triggers a TT8v2 master clear. The
system reinitializes, detects the absence of an operator and starts the URAO feature.
Standard MMP Sensors
The MMP standard instrument suite is comprised of two sensors a CTD and an ACM.
Integrating other sensors to the MMP requires a partnership with McLane.
The TT8v2 communicates with each of the sensors through a dedicated RS-232 serial
port. The sensors are turned on and start logging internally at the beginning of each profile.
When the profile is completed, logging is stopped and the data is transferred to the flash card.
CTD Measurements
The CTD logs one measurement each of conductivity, temperature, and depth in each
record and acquires records at a nominal rate of 1.85 Hz. Each datum is stored as a scaled integer
in three bytes. There are, therefore, nine bytes in a CTD record and the CTD can log records
internally for approximately 8.75 hours before filling its 512 Kbyte data memory. The measured
current drain of the CTD is 12.5 mA while logging internally (profiling) and 30 mA while
Appendix B-9