Kevins investigation of GPS NMEA data sentences from a
Garmin GPS 12XL

GPS 12XL Interface Setting:
	Garmin NONE/NMEA 0183 V2.0, 4800 baud,
PC Interface Setting (direct cable connection to PC serial port):
	Used "Hyperterm", direct to com 1, 4800 baud, 8-N-1


Packets of data were being sent approx. once per second.  Each
packet contains a variable number of NMEA sentences.  Below is a
typical packet sent with the 12XL in simulator mode:

$GPRMC,175741,A,4751.698,N,12209.774,W,000.0,360.0,191100,019.5,E*69
$GPRMB,A,,,,,,,,,,,,V*71
$GPGGA,175742,4751.698,N,12209.774,W,1,09,2.0,128.0,M,-18.2,M,,*78
$GPGSA,A,3,01,04,,13,19,20,22,24,27,28,,,3.3,2.0,3.0*37
$GPGSV,3,1,10,01,71,307,50,04,22,299,42,06,01,033,00,13,77,327,51*7B
$GPGSV,3,2,10,19,37,233,45,20,61,185,49,22,44,103,47,24,09,332,37*7A
$GPGSV,3,3,10,27,16,232,39,28,33,148,45,,,,,,,,*75
$PGRME,15.0,M,22.5,M,15.0,M*1B
$PGRMM,WGS 84*06
$GPRTE,1,1,c,0*07


Details of RMC and GGA sentences.  All data sent are printable ASCII
data.  Each field is seperated by a comma.  (Note fields can be of variable
length):

$GPRMC,175741,A,4751.698,N,12209.774,W,000.0,360.0,191100,019.5,E*69

$	  =	Start of sentence symbol
GP	  =	GPS receiver talker
RMC	  =	Recommended Minimum GPS data
175741	  =	Time of fix: 17:57:41 UTC
A	  =	A = OK (V = warning)
4751.698  =	Latitude 47 deg, 51.698 minutes
N	  =	North latitude
12209.774 =	Longitude 122 deg, 09.774 minutes
W	  =	West longitude
000.0	  =	Speed over ground, Knots
360.0	  =	Course made good direction, relative to true north
191100	  =	Date of fix: 11/19/00 (November 19th, 2000)
019.5	  =	Magnetic variation, 19.5 deg
E	  =	East magnetic variation
*	  =	Start of checksum symbol
69	  =	Two digit (Hex) checksum (exclusive OR of all chars
		between, but not including the "$" and "*")
		
		
$GPGGA,175742,4751.698,N,12209.774,W,1,09,2.0,128.0,M,-18.2,M,,*78

$	  =	Start of sentence symbol
GP	  =	GPS receiver talker
GGA	  =	Global Positioning System fix data
175742	  =	Time of fix: 17:57:42 UTC
4751.698  =	Latitude 47 deg, 51.698 minutes
N	  =	North latitude
12209.774 =	Longitude 122 deg, 09.774 minutes
W	  =	West longitude
1	  =	Fix Quality (0 = invalid, 1 = GPS fix, 2 = DGPS fix)
09	  =	Number of satellites being tracked
2.0	  =	Horizontal dilution of position
128.0	  =	Altitude above Mean Sea Level (may be negative)
M	  =	Altitide units (meters)
-18.2	  =	Height of geoid (mean sea level) above WGS84 ellipsiod
M	  =	Geoid height units (meters)
(empty)	  =	Time in seconds since last DGPS update
(empty)	  =	DGPS Station Number