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Appendix A
Wiring and Interfacing
Connecting the Power/Data Cable
The power/data cable connects the GPSMAP 188/238 Sounder to a 8-35 (GPSMAP 188C 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 Dif-
ferential GPS (DGPS), NMEA 0183 version 2.3*, RTCM SC-104 input (version 2.0).
The following are the sentences for NMEA 0183, version 2.3* output:
Approved sentences— GPBWC, GPRMC, GPGGA, GPGSA, GPGSV, GPGLL, GPBOD, GPRMB, GPRTE,
GPVTG, GPWPL and GPXTE. Proprietary sentences— PGRME, PGRMZ, and PSLIB.
The GPSMAP 188/188C/238 Sounder also includes NMEA input with support for the WPL sentence
and sonar NMEA input with support for the DPT (Depth), MTW (Water Temp) and VHW (Water
Speed & Heading) sentences. If connecting to COM2 for sonar NMEA input, the unit interface must be
set to NMEA In/NMEA Out (see page 89-90). If connecting to COM1, the unit must be set to NMEA
In/NMEA Out.
COM 2 Rx
COM 2 Tx
COM 1 Tx
COM 1 Rx
DC Power
Source
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
proprietary communication protocol from the
Help and Support section of our web site at
www.garmin.com.
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:
GPSMAP 188/238 AGC/3AG - 2 Amp
GPSMAP188C - AGC/3AG - 5 Amp
(Cable View)
DC Positive
(RX COM 1)
(TX COM 1)
(RX COM 2)
(TX COM 2)
*GPSMAP 188C with software version 5.20 and GPSMAP 188/238 with software version 4.20 or higher will
use NMEA 0183, version
3.01. No additional NMEA sentences have been added or removed in 3.01.