ComNav P4 Installation and Operation
Document PN 29010100 V1r0 - 69 -
RS-232 Electrical Signals
It is common for non-marine equipment (especially PCs) to be able to transmit and
receive
NMEA-formatted data, but not using the RS-422 electrical interface specified in
the NMEA
Standard. Instead using another electrical interface, RS-232. A prime example
is the “COM port” on a Personal
Computers, which is always at RS-232 levels.
An RS-232 interface, in contrast to RS-422, does not use differential-signal wiring. Instead,
a
single wire is used for each of the main signals – Receive (usually labelled “Rx”) and
Transmit
(“Tx”) – and for the Signal Ground (“Gnd”). The voltage levels are also different
than RS-422 (There are also several RS-232 status signals, but these are not used in the
P4).
Such equipment (often described as being “NMEA compatible”) can usually be connected
directly to the P4, although there is some risk of reduced electrical noise
immunity. See the
PC COM Ports section in Appendix 1 for more details.
LED Status Indicators
When the autopilot is turned on, the Status LED labelled NMEA 0183 IN #1 in the SPU’s
diagnostic section will be flashing whenever the autopilot is receiving data on NAV1 - IN.
Similarly, the NMEA 0183 #2 LED will be flashing whenever the autopilot is receiving data on
NAV2 - IN.
Typically, an LED will flash at a rate of about once per second for regular data from a GPS or
Chart-plotter. It will typically flash at a rate of about ten times per second when connected to
a Heading source, such as the G2 GPS Compass.
If the LED for a given port is flashing, but you are seeing INVALID or NO DATA
Navigation
(Heading, Speed, Course, NAV) error messages for that port on the
Control Head, and yet
you are sure the other device is in fact sending valid data,
try reversing the wires connected
to NAV1 – IN, or NAV2 – IN. It is possible that
the other device’s signal names are not
NMEA’s `A´ and `B´ (see Table 3),
and so might have been connected the wrong way round;
reversing the wire pair
at J6 often solves this situation.
NOTE: The LEDs only show that data is being received on the associated Nav1 (or
Nav2)
port. They do not mean that the data received is valid. If you are still seeing error messages,
something else is wrong. Contact your
ComNav Dealer for assistance.
Other Connections
Thruster Interface
The J11 – THRUSTER I’ FACE connector is used with the CT7 Thruster Interface.
The
receptacle is not supplied with a mating plug, since the required plug is supplied
with the
CT7.
Final Steps and Post-Installation Checks
Before using the P4 for the first time, please verify that the entire
system and all its
components are safely and securely mounted, and will not shake loose from
the vibrations
that can be expected in a marine vessel.
Installation
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