[ Short extract from the Garmin GPS 35 LP manual - the original
manual is in PDF format available from the Garmin web site:
http://www.garmin.com ]


Appendix C

Phase Output Data Binary Format

Two records are transmitted once per second by the GPS 35LP. One record
contains primarily post-process information such as position and velocity
information. The second record contains receiver measurement information.
The records are sent at a default baud rate of 9600 baud, 8 bits, no parity.

Records begin with a delimiter byte (10 hex). The second byte identifies the
record type (28 hex for a position record, 29 hex for a receiver
measurement). The third byte indicates the size of the data. The fourth byte
is the first byte of data. The data is then followed by a chksum byte, a
delimiter byte (10 hex), and an end-of-transmission character (03 hex).

Note - If RTCM-104 differential data is sent to the GPS 35LP the board will
reset the Phase Output Data baud rate to the same baud rate used for
RTCM-104 data. If the differential inputs are used on the GPS 35LP then the
RTCM-104 data must be sent to the GPS 35LP at 9600 baud(preferred) or 4800
baud. RTCM-104, baud rates less than 4800 baud are not supported by the GPS
35LP since it would limit bus bandwidth past the point where a once per
second phase output data rate could be maintained.


Position Record

- 0x10 (dle is first byte)
- 0x28 (position record identifier)
- 0x36 (size of data)
- cpo_pvt_type (see description below)
- one byte chksum (the addition of bytes between the delimiters should equal
0)
- 0x10 (dle)
- 0x03 (etx is last byte)

typedef struct
{
  float alt;
  float epe;
  float eph;
  float epv;
  int fix;
  double gps_tow;
  double lat;
  double lon;
  float lon_vel;
  float lat_vel;
  float alt_vel;
} cpo_pvt_type;

alt ellipsoid altitude (mt)
epe est pos error (mt)
eph pos err, horizontal (mt)
epv pos err, vertical (mt)
fix 0 = no fix; 1 = no fix; 2 = 2D; 3 = 3D; 4 = 2D differential; 5 = 3D
differential;
6 and greater - not defined
gps_tow gps time of week (sec)
lat Latitude (rad)
lon Longitude (rad)
lon_vel Longitude velocity (mt/sec)
lat_vel Latitude velocity (mt/sec)
alt_vel Altitude velocity (mt/sec)

Receiver Measurement Record

- 0x10 (dle is first byte)
- 0x29 (receiver record identifier)
- 0xE2 (size of data)
- cpo_rcv_type (see below)
- one byte chksum (the addition of bytes between the delimiters should equal
0)
- 0x10 (dle)
- 0x03 (etx)

typedef struct
{
unsigned long cycles;
double pr;
unsigned int phase;
char slp_dtct;
unsigned char snr_dbhz;
char svid;
char valid;
} cpo_rcv_sv_type;

typedef struct
{
double rcvr_tow;
int rcvr_wn;
cpo_rcv_sv_type sv[12];
} cpo_rcv_type;

rcvr_tow Receiver time of week (sec)
rcvr_wn Receiver week number
cycles Number of accumulated cycles
pr pseudo range (mt)
phase to convert to (0 -359.999) multiply by 360.0 and divide by 2048.0
slp_dtct 0 = no cycle slip detected; non 0 = cycle slip detected
snr_dbhz Signal strength
svid Satellite number (0 - 31) Note - add 1 to offset to current svid numbers
valid 0 = information not valid; non 0 = information valid

dle and etx bytes:

Software written to receive the two records should filter dle and etx bytes
as described below:

typedef enum
{
dat,
dle,
etx
} rx_state_type;
char in_que[256];
int in_que_ptr = 0;
rx_state_type rx_state = dat;
void add_to_que( char data )
{
#define dle_byte 0x10
#define etx_byte 0x03
if (rx_state == dat)
{
if (data == dle_byte)
{
rx_state = dle;
}
else
{
in_que[ in_que_ptr++ ] = data;
}
}
else if (rx_state == dle)
{
if (data == etx_byte)
{
rx_state = etx;
}
else
{
rx_state = dat;
in_que[ in_que_ptr++ ] = data;
}
}
else if (rx_state == etx)
{
if (data == dle_byte)
{
rx_state = dle;
}
}
if (in_que_ptr > 255)
{
in_que_ptr = 0;
}
}


[ This from a few pages later - these are the outputs of some DOS
programs supplied with the dev kit]


File Formats

ALMANAC.DAT

Example almanac entry:
**** Week 794 almanac for PRN-01 ************
ID: 01
Health: 000
Eccentricity: 3.414630890E-003
Time of Applicability(s): 380928.0000
Orbital Inclination(rad): 9.549833536E-001
Rate of Right Ascen(r/s): -7.771752131E-009
SQRT(A) (m^1/2): 5153.589843
Right Ascen at TOA(rad): 8.032501489E-002
Argument of Perigee(rad): -1.308424592E+000
Mean Anom(rad): 2.045822620E+000
Af0(s): 9.536743164E-007
Af1(s/s): 8.367351256E-011
week: 794
Almanac information for satellites with a bad health status will not be
included in this file when
downloaded from the GPS25 sensor and should not be included when uploading
to the GPS25 sensor.

EPHEMERS.DAT

Example ephemeris entry:
**** Week 794. Ephemeris for PRN-18 **********
Ref Time of Clk Parms(s): 233504.000000
Ref Time of Eph Parms(s): 233504.000000
Clk Cor, Group Dly(s): -8.280389E-006
Clk Correction af1(s/s): -3.410605E-013
Clk Correction af2(s/s/s): 0.000000E+000
User Range Accuracy(m): 33.299999
Eccentricity(-): 5.913425E-003
SQRT(A) (m**1/2): 5.153628E+003
Mean Motion Cor(r/s): 4.710911E-009
Mean Anomaly(r): 6.033204E-001
Argument of Perigee(r): 1.418009E+000
Right Ascension(r): 3.520111E-002
Inclination Angle(r): 9.434418E-001
Rate of Right Asc(r/s): -8.210699E-009
Rate of Inc Angle(r/s): 4.503759E-010
Lat Cor, Sine(r): 1.212582E-005
Lat Cor, Cosine(r): 2.004206E-006
Inc Cor, Sine(r): -1.490116E-008
Inc Cor, Cosine(r): -9.872019E-008
Radius Cor, Sine(m): 38.375000
Radius Cor, Cosine(m): 132.937500
Issue of Data : 184


Ephemeris Record

- 0x10 (dle is first byte)
- 0x2A (ephemeris record identifier)
- 0x94 (size of data)
- eph_type (see description below)
- one byte chksum (the addition of bytes between the delimiters should equal
0)
- 0x10 (dle)
- 0x03 (etx)
typedef struct /* ephemeris record */
{
char svid; /* Satellite number (0 - 31) */
int wn; /* week number (weeks) */
float toc; /* reference time of clock parameters (s) */
float toe; /* reference time of ephemeris parameters (s) */
float af0; /* clock correction coefcnt - group delay (s) */
float af1; /* clock correction coefficient (s/s) */
float af2; /* clock correction coefficient (s/s/s) */
float ura; /* user range accuracy (m) */
double e; /* eccentricity (-) */
double sqrta; /* square root of semi-major axis (a) (m**1/2) */
double dn; /* mean motion correction (r/s) */
double m0; /* mean anomaly at reference time (r) */
double w; /* argument of perigee (r) */
double omg0; /* right ascension (r) */
double i0; /* inclination angle at reference time (r) */
float odot; /* rate of right ascension (r/s) */
float idot; /* rate of inclination angle (r/s) */
float cus; /* argument of latitude correction, sine (r) */
float cuc; /* argument of latitude correction, cosine (r) */
float cis; /* inclination correction, sine (r) */
float cic; /* inclination correction, cosine (r) */
float crs; /* radius correction, sine (m) */
float crc; /* radius correction, cosine (m) */
byte iod; /* issue of data */
} eph_type;
To initiate an ephemeris download for all tracked satellites send the
following bytes in sequence:
0x10, 0x0D, 0x04, 0x02, 0x0C, 0x0, 0x0, 0xE1, 0x10, 0x03

GPS25PM.DAT
Example data file entry:

TIM time_of_week week_number
RCV svid snr (T)rack/(C)ycle_slip phase pseudo_range cycles
PVT time lat lon alt lat_vel lon_vel alt_vel epe eph epv
TIM 235537.99855650 794
RCV 18 50 T 120.2 19964528.44 2068193
RCV 29 50 T 133.2 20364313.25 1950557
RCV 28 45 T 176.5 21135153.13 2069992
RCV 19 47 T 145.2 21190271.83 2182643
RCV 31 45 T 75.8 21240354.20 2216421
RCV 22 42 T 195.1 22849183.41 1855826
RCV 27 36 T 155.2 24234175.55 2230462
RCV 14 39 T 202.3 25147694.34 1845263
PVT 235537.99999842 38.9499588 94.7463684 211.7 -0.19 -0.31 0.13 28 16 23
TIM 235538.99853500 794
RCV 18 50 T 38.8 19958107.10 2101947
RCV 29 50 T 132.4 20358247.54 1982431
RCV 28 45 T 189.5 21128713.01 2103829
RCV 19 47 T 284.6 21183470.16 2218374
RCV 31 45 T 19.0 21233441.89 2252746
RCV 22 42 T 263.0 22843381.08 1886300
RCV 27 36 T 311.7 24227194.88 2267146
RCV 14 39 T 308.3 25141899.86 1875708
PVT 235538.99999827 38.9499550 94.7463684 212.6 -0.19 -0.30 0.14 28 16 23
TIM 235539.99851349 794
RCV 18 50 T 76.6 19951681.26 2135704
RCV 29 50 T 284.4 20352180.11 2014308
RCV 28 45 T 320.8 21122272.68 2137669
RCV 19 47 T 8.3 21176671.33 2254110
RCV 31 45 T 170.2 21226528.82 2289074
RCV 22 42 T 315.9 22837584.50 1916778
RCV 27 36 T 132.4 24220207.85 2303835
RCV 14 39 T 127.4 25136106.23 1906158
PVT 235539.99999812 38.9499512 94.7463684 213.5 -0.19 -0.30 0.13 28 16 23
TIM 235540.99849199 794
RCV 18 50 T 174.9 19945258.21 2169465
RCV 29 50 T 177.7 20346113.87 2046190
RCV 28 45 T 159.6 21115834.07 2171514
RCV 19 47 T 324.7 21169868.61 2289849
RCV 31 45 T 111.8 21219615.05 2325407
RCV 22 42 T 261.7 22831782.87 1947261
RCV 27 36 T 259.1 24213226.41 2340528
RCV 14 39 T 318.7 25130310.86 1936612
PVT 235540.99999797 38.9499474 94.7463760 214.4 -0.19 -0.30 0.14 28 16 23
TIM 235541.99847244 794
RCV 18 50 T 325.5 19938831.69 2203229
RCV 29 50 T 152.1 20340045.44 2078075
RCV 28 45 T 52.4 21109392.21 2205362
RCV 19 47 T 125.3 21163068.15 2325593
RCV 31 45 T 159.4 21212700.30 2361743
RCV 22 43 T 117.1 22825981.54 1977748
RCV 27 36 T 352.1 24206248.88 2377225
RCV 14 39 T 141.3 25124515.72 1967071
PVT 235541.99999977 38.9499474 94.7463760 215.4 -0.19 -0.30 0.13 28 16 23