ComNav Vector G2 & G2B Installation & Operation Installation
Document PN 29010078 V2.0 - 29 -
DRAFT #3 – 29 May 2009
RS-232
The only electrical standard specified in NMEA 0183 is RS-422. However, it is common for
non-marine equipment to be able to accept NMEA-formatted data – not at RS-422 levels, but
only at RS-232 levels; for example, the “COM port” on a PC is always at RS-232 levels.
Such equipment (often described as being “NMEA compatible”) will require using one or both
of the G2’s RS-232 outputs.
The G2’s Transmit (Tx) signal wire(s) must be connected to the Receive (Rx) pin(s) of the
other device.
Inputs
Both ports’
Receive in
puts (Rx wires) are at RS-232 levels only.
The Receive inputs are used for controlling the G2 (with commands sent to it on Port A – to
enable sentences, set update rates, set Baud rates, etc.), and for firmware upgrades (via the
input of Port B).
Either port may also be used for receiving DGPS correction data (RTCM SC-104) from an
external-source – see page 40.
If you are going to use the
G2’s
RS-232 input connections, the
Tx signal wire(s) from the
other device must be connected to the
Rx wire(s) of the G2.
Signal Grounds
Whether or not to connect the G2’s Signal Ground to the Signal Ground (or the Main or
Power Ground, if there is no Signal Ground) of the other device or devices on your vessel
depends on how your vessel, and any other equipment, is wired.
• RS-422: per the NMEA 0183 Standard, the Listener will have optically (or
galvanically) isolated RS-422 inputs; thus, it is usually not strictly necessary – and
sometimes it is not even possible – to connect the Grounds.
⇒ For example, the Commander P2’s NAV1/2 inputs (NMEA 0183 Listeners) are
optically isolated – no Signal Ground pin for those inputs is provided.
In contrast, for the P2’s NAV output (which is an NMEA Talker), there is a
Ground pin – but that is a “current-controlled, AC-coupled” ground, not the P2’s
main Signal Ground.
• RS-232: the G2’s RS-232 Signal Ground
MUST be connected to the other device’s
Signal Ground, when using the RS-232 ports.
Caution! The G2’s RF Shield wire (the bare wire in the cable) must not be
connected at the other device, no matter whether RS-422 or RS-232
signal wires – or both – are being used. Cut it back near the end of the
cable’s outer jacket, and insulate the stub with electrical tape.
• On the other hand, it is sometimes better – from the perspective of signal integrity
and/or electrical noise-reduction – to connect some or all of the Grounds in a system.
Consult your ComNav Dealer for help, if you are unsure what will work best on your vessel.
Serial Port Settings
Both ports use ordinary asynchronous serial data formatting, as specified in the NMEA 0183
Standard; the formatting is fixed, and can not be changed:
• 1 Start Bit, 8 Data bits, No Parity Bit & 1 Stop Bit (commonly described as “8-N-1”).
The baud rates of the G2’s serial ports must be the same as the device(s) to which they are
connected. The factory-default configuration is 4800 Baud on both ports – per the
NMEA 0183 Standard.
The baud rates can be changed, if you need to; also, Port A and Port B may have different
Baud rates. See pages 48 & 61 for more details.
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