2.6
Time Synchronization (for Non-Integrated Systems)
Timing is crucial for synchronizing signals from the sonar, GNSS and IMU. Only the WBMS requires
PPS & NMEA ZDA hardware input. All integrated WBMS systems receive timing from the internal
GNSS card. The system can handle baud rates from 4800 to 115200 and will have no problem
maintaining sync with other NMEA messages output on the same port as the ZDA+PPS. Ensure
that the baud rate is fast enough to allow throughput of all strings.
The PPS can be input in two ways:
• To BNC “PPS” connector on SIU
• To Serial “GPS” DB9 connector on SIU (pin 9 for pulse & pin 5 for ground)
The PPS signal can be either active low or active high. The SIU synchronizes to the falling edge of
an active low signal, or the rising edge of an active high signal. The voltage on the PPS should not
exceed 5V, doing so may cause unwanted issues. In addition, the time duration should be 1µ-200ms.
For the standalone WBMS, the SIU should receive a PPS TTL input at 3.3V (5V tolerant). The SIU
can autodetect negative or positive PPS input and has ±15kV ESD protection, ±60V fault protection.
The integrated GNSS/INS WBMS systems can output a (positive or negative configurable) PPS TTL
signal at 5V. However, this is NOT fault protected and is rated for a maximum absolute voltage of
6V.
CAUTION: Don’t Connect Active PPS to SIU for Integrated Systems
The integrated versions of the SIU outputs PPS pulses. Attaching an active
PPS cable to this port will damage internal electronics and void the warranty.
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