Maretron GPS200 - Manual (Page 20)

GPS200 User’s Manual
Page A4 Appendix A – NMEA 2000
®
Interfacing Revision 1.2
4: Reserved (2 bits) – This field is reserved by NMEA; therefore, this field always
contains a value of 0x3 (the GPS200 sets all reserved bits to a logic 1)
5: HDOP – This field is used to indicate the horizontal dilution of precision with a
resolution of 1x10
-2
(unitless).
6: VDOP – This field is used to indicate the vertical dilution of precision with a
resolution of 1x10
-2
(unitless).
7: TDOP – This field is used to indicate the time dilution of precision with a resolution of
1x10
-2
(unitless).
PGN 129540 – GNSS Satellites in View
The GPS200 uses this PGN to provide the GNSS information on current satellites in view
tagged by sequence ID. Information includes PRN, elevation, azimuth, and SNR. Field 4
defines the number of satellites. Fields 5 through 11 defines the satellite number and the
information. Fields 5 through 11 are sequentially repeated for each satellite to be transmitted.
The factory default for periodic transmission rate is once per second. The transmission of this
PGN can be disabled or the transmission rate of this PGN can be changed (see PGN 126208
– NMEA Request Group Function – Transmission Periodic Rate).
Field 1: SID – The sequence identifier field is used to tie related PGNs together. For
example, the GPS200 will transmit identical SIDs for 126992 (System Time), 128259
(Speed), 129026 (COG and SOG, Rapid Update), 129029 (GNSS Position Data),
129539 (GNSS DOPs), and 129540 (GNSS Satellites in View) to indicate that the
readings are linked together (i.e., the data from each PGN was taken at the same
time although they are reported at slightly different times).
2: Mode – This field always reads as 3 (Null), indicating that range residuals are used
to calculate position, and not calculated after the position.
3: Reserved (6 bits) – This field is reserved by NMEA; therefore, this field always
contains a value of 0x3F (the GPS200 sets all bits to a logic 1)
4: Number of SVs – This field is used to indicate the number of current satellites in
view. Fields 5-11 are repeated the number of times specified by this field’s value.
5: PRN "1" – This field is used to indicate the Satellite ID Number of the satellite (1-
32=GPS, 33-64=SBAS, 65-96=GLONASS).
6: Elevation "1" – This field is used to indicate the Elevation of the satellite.
7: Azimuth "1" – This field is used to indicate the Azimuth of the satellite.
8: SNR "1" – This field is used to indicate the Signal to Noise Ratio (SNR) of the
satellite.
9: Range Residuals “1” – The GPS200 always sets this field to a value of 0x7FFFFFFF
(data not available)
10: PRN Status "1" – This field is used to indicate the status of the first satellite in the
list. (0=Not Tracked, 1=Tracked but not used in solution, 2=Used in solution without
Differential corrections, 3=Differential Corrections available, 4=Tracked with
Differential Corrections, 5=used with Differential Corrections)
11: Reserved (4 bits) – This field is reserved by NMEA; therefore, this field always
contains a value of 0xF (the GPS200 sets all bits to a logic 1)
If Field 4 contains a value greater than one, then the group of fields 5 through 11 is repeated
until this group appears the number of times indicated by the value of Field 4.