ComNav Vector G2 & G2B Installation & Operation Installation
Document PN 29010078 V2.0 - 36 -
DRAFT #3 – 29 May 2009
The PC would typically be running a Navigation program (e.g., programs from Fugawi™,
Jeppesen®/Nobeltec®, Rose Point Navigation, or similar), replacing the Navigation control
functions of (or as a backup to) the Chartplotter.
In this connection scheme, the PC will need to be hooked to the G2 via the latter’s RS-232
connections – but it will also usually be necessary to connect the PC to the autopilot and/or
other NMEA 0183 equipment, at the NMEA Standard’s RS-422 signal levels.
⇒ Since very few PCs have built-in RS-422 ports, an RS-232 ⇔ RS-422 Convertor
will usually also be needed (as shown in Figure
15).
Alternatively, if your PC has USB ports, a USB-to-422 adapter could be used for
the PC-to-autopilot/etc. connection.
Contact your ComNav Dealer for ordering information.
Note: it is sometimes possible to mix the RS-232 electrical levels of a PC’s COM port with
the NMEA 0183 Standard’s RS-422 levels – driving into an RS-422 input from the PC’s
RS-232 output, and/or vice-versa.
For an example, see the section describing NMEA connections to the Commander P2
SPU’s NAV ports, in the P2’s Installation & Operation Manual. This method usually
works fine … on the P2 (& also on the Admiral P3), at any rate.
But it depends largely on the electrical drive capabilities of the PC’s COM port circuits.
As well, in a technical sense, it violates the rules of the NMEA 0183 Standard, since
the voltage levels, signal rise/fall times and circuit impedances of RS-232 and RS-422
are different. It may also cause electrical noise problems – RS-232 is “single-ended”
wiring, whereas RS-422 is “differential” (i.e., twisted-pair wires) and thus withstands
RFI & EMI electrical noise better.
For those reasons, ComNav strongly recommends against mixing RS-232 & RS-422!.
However, if you wish to try it with a P2 or P3 SPU:
• Wire the G2’s Port A RS-232 Tx signal to the PC COM port’s Rx signal, and wire
the RS-232 Signal Ground, both as shown in Figure 15.
• Wire the PC COM p
ort’s RS-232 Tx signal to the IN-2A pin of the P2/P3 SPU’s
J9, and the PC’s RS-232 Signal Ground to the SPU’s IN-2B pin.
• If the PC has only one COM port, but you need to run both “Navigation” & “G2
Control” programs on the PC (see below), you can also connect the PC’s Tx
signal & Ground to the G2’s Port A RS-232 Rx & Signal Ground wires, in parallel
to connecting them to a P2/P3.
L Caution! You can NOT do the same for the Rx signal – i.e.,
connect both the G2’s Tx signal and the P2/P3’s NAV OUT
signal to the PC’s Rx pin. Doing so will damage either the G2 or
the P2/P3 … or both.
L If you encounter any problems with this wiring scheme, use of an
RS-232
⇔
RS-422 Convertor will then be required.
Using a PC for both Vector G2 Control/Display & a Navigation Program
The PC can b
e
used simultaneously for both display & control of the G2, and for Navigation
display & control. In this scheme, two COM ports on the PC will be required (or multiple
USB-to-Serial adapters, or a multi-port USB adapter).
The wiring for this scheme typically will be the same as Figure
15.
Two programs will need to be running on the PC:
• One program for Navigation display & control
• One program for controlling the G2 and displaying its output
Selection of which COM port on the PC to assign for “Navigation” use, and which port for
“Vector G2” use, as well as Baud rates, will depend on the programs used.
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