Appendix C

Phase Output Data Binary Format

Two records are transmitted once per second by the GPS 35LP. One record contains primarily postprocess 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)

29