4.1.3 Serial Communication
All serial interfacing is standard RS-232 protocol.
Table 7: DB-9M RS-232 Standard Protocol
Table 8: SIM DB-9M Serial pin assignment
4.1.4 Time and PPS input
4.1.4.1 Connecting PPS and Time to the SIM
In order to provide the most accurate multibeam data possible, the Sonic 2024/2022 takes in the
GPS Pulse Per Second (PPS) and NMEA ZDA time message or an ASCII UTC message, which is
associated with the pulse, to accurately time stamp the Sonic 2024/2022 data. The data collection
software will take in the same PPS and time message to synchronise the computer clock and the
auxiliary sensor data.
The PPS is a TTL (transistor – transistor logic) pulse. The SIM box PPS input threshold is ≈ +1.35V
with about 0.14V of hysteresis. The PPS input rejects pulses narrower than about a microsecond to
reject high frequency cable reflections and ringing, but not all types of noise. The input pulse timing
needs to be stable, within about 100ppm, or the SIM box will reject the pulses and the LED will flash
red instead of green. The pulse is transmitted to the SIM and the data collection computer via a
coaxial cable (such as RG-58); the cable is terminated with BNC connectors so that it is easy to use a
‘T’ adaptor to parallel the PPS to different locations. Connect one end of the coaxial cable to the
GPS receiver’s PPS output (via a ‘T’ adaptor, if required) and the other end to the SIM BNC labelled
PPS. When a pulse is received, the LED next to the BNC connector will flash green at 1 Hz.
Figure 27: TTL input/output (PPS and Sync In/Out) schematic
(electrostatic discharge)
protection; it trips at
Page 38 of 210
Version 5.0 Rev r002
Date 05-08-2014
Part No. 96000001
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