Interface Setup
The GPS 12’s interface page lets you specify the for-
mats for connecting external devices. There are six
options: GRMN/GRMN, None/None, RTCM/None,
RTCM/NMEA, NMEA/NMEA, and None/NMEA. Each
option lists the input format first, followed by the out-
put format.
To select an I/O format:
1. Highlight the I/O field and press
E
.
2. Select the desired setting and press
E
.
The GRMN/GRMN setting is a proprietary format
that lets you exchange information such as waypoints,
routes, and track logs between two GARMIN GPS units
or the GPS 12 and a PC. The transfer mode field is
directly below ‘GRMN/GRMN’, and allows you to spec-
ify what information to request or send to a second
GPS unit. The ‘Host’ setting lets you control all data
transfer functions from the second GPS unit or a PC.
To select a transfer mode:
1. Highlight the transfer mode field and press
E
.
2. Select a desired setting, and press
E
.
To disable all interfacing capabilities, select the
‘None/None’ setting. If you want to output NMEA data
without any differential input capability, select
‘None/NMEA’.
Interface Setup: DGPS
The last two format settings allow the differential-
ready GPS 12 to accept RTCM DGPS corrections in
RTCM 104 version 2.0 format. Using DGPS corrections
will improve receiver accuracy to 1-5 meters, regardless
of errors induced by the U.S. Dept. of Defense Selective
Availability (SA) program. Two RTCM options are avail-
able: ‘RTCM/NONE’, which allows connection to a bea-
con receiver with no output capability; and ‘RTCM/
NMEA’, which allows DGPS input and NMEA output.
When ‘RTCM/NMEA’ is selected, the GPS 12 will
either automatically try to tune the last frequency and
bit rate you selected or will switch to the default fre-
quency of 304.0 kHz with a bit rate of 100 bps if no
previous beacon has been tuned. (You may also enter
your own frequency and bit rate if desired.) This infor-
mation is used to tune/control an optional GARMIN
GBR 21 differential beacon receiver. Note: Use the
‘RTCM/NONE’ setting if your beacon receiver does not
support these software-driven controls.
47
The ‘GRMN/GRMN’ op-
tion allows the GPS 12 to
exchange data with a PC
or another GPS unit. Use
this setting with the
optional PC Software Kit.
REFERENCE
Interface Setup
& DGPS
Select the ‘RTCM/NMEA’
option to use the GPS 12
along with a GBR 21
D i ff e rential Beacon
Receiver.
GPS12B 1/13/99 4:29 PM Page 47
