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Appendix A
Wiring and Interfacing
Connecting the Power/Data Cable
The power/data cable connects the GPSMAP 178/178C to 10-35 volt DC system and provides
interface capabilities for connecting external devices. The color code in the diagram below indicates the
appropriate harness connections.
Interfacing
The following formats are supported for connection of external devices: Garmin proprietary Differen-
tial GPS (DGPS), NMEA 0183 version 3.01, RTCM SC-104 input (version 2.0).
The following are the sentences for NMEA 0183, version 3.01 output:
Approved sentences— GPBWC, GPRMC, GPGGA, GPGSA, GPGSV, GPGLL, GPBOD, GPRMB, GPRTE,
GPVTG, GPWPL and GPXTE. Sonar— SBDDBT, SDDPT, SDMTW, and SDVHW Proprietary sentences—
PGRME, PGRMZ, and PSLIB.
(red)+10-35VDC
(black)-Ground(Power/Data)
(blue) Port1DataOUT
(brown)Port1DataIN
(white)Port2DataIN
(green)Port2DataOUT
(yellow)AlarmLow
To Transducer
To Unit
Beacon
Receiveror
DSCVHF
Autopilot/
NMEADevice
DC�
PowerSource
RXD+
RXD-
RX+
TX+
AlarmRelay
100mamax
coilcurrent
Note: During a typical installation,
only the Red and Black wires are used.
The other wires do not have to be con-
nected for normal operation of the unit.
Replacement fuse: AGC/3AG - 2.0 Amp
(Cable View)
Pin 16 - Brown (RX COM 1)
Pin 17 - Blue (TX COM 1)
Pin 13 - White (RX COM 2)
Pin 14 - Green (TX COM 2)
Pin 11 - Yellow (Alarm)
Pin 15 - Red (DC Positive)
Pin 18 - Black (Ground)
Complete information concerning
NMEA & RTCM formats and
sentences is available for purchase
from NMEA at:
NMEA
Seven Riggs Avenue
Severna Park, MD 21146
U.S.A.
410-975-9425
410-975-9450 FAX
www.nmea.org
Radio Technical Commission For
Maritime Services (RTCM)
1800 Diagonal Road, Suite 600
Alexandria, VA 22314-2480
U.S.A.
703-684-4481 (Info Only)
703-836-4229 FAX
www.rtcm.org
You can download a copy of Garmin's propri-
etary communication protocol from the Help
and Support section of our web site at www.
garmin.com