The SG-959 interface protocol is based on the National Marine Electronics Association (NMEA)
interface specification, namely, the NMEA 0183 standard.The SG-959 is capable of supporting
following NMEA message formats specifically developed and defined by SiRF.
NMEA Message PrefixFormatDirection
$GPGGATime, position and fix type data.Out
$GPGLLLatitude, longitude, time of position fix and status.Out
$GPGSAGNSS DOP and active satellitesOut
$GPGSVSatellites in view.Out
$GPMSS
$GPRMCRecommended minimum specific GNSS data.Out
$GPVTGSpeed and course over ground.Out
$GPZDADate and time.Out
Radio beacon signal-to-noise ratio, signal strength,
Out
frequency, etc.
General NMEA Format
The general NMEA format consists of an ASCII string commencing with a ‘$’character and
terminating with a <CR><LF> sequence.NMEA standard messages commence with ‘GP’then a
3-letter message identifier.The message header is followed by a comma delimited list of fields
optionally terminated with a checksum consisting of an asterix ‘*’and a 2 digit hex value
representing the checksum.There is no comma preceding the checksum field.When present,
the checksum is calculated as a bitwise exclusive of the characters between the ‘$’ and ‘*’.As an
ASCII representation, the number of digitsin each number will vary depending on the number and
precision, hence the record length will vary.Certain fieldsmay be omitted if they are not used, in
which case the field position is reserved using commas to ensure correct interpretation of
subsequent fields.
This message transfersinformation about satellitesin view.The $GPGSV message structure is
shown below.Each record contains the information for up to 4 channels, allowing up to 12
satellites in view.In the final record of the sequence the unused channel fields are left blank with
commas to indicate that a field has been omitted.Following isan example.
Message ID$GPGSVGSA protocol header.
Number of messages
Message number1Sequence number, range 1 to 3.
Satellites in view07Number of satellites currently in view.
(1)
2Number of messages, maximum 3.
Satellite ID07Channel 1, ID range 1 to 32.
Elevation79degreeElevation of satellite, maximum 90.
Azimuth048degreeAzimuth of satellite, range 0 to 359.
SNR (C/N0)42dBHzRange 0 to 99, null when not tracking.
Satellite ID02Channel 2, ID range 1 to 32.
Elevation51degreeElevation of satellite, maximum 90.
Azimuth062degreeAzimuth of satellite, range 0 to 359.
SNR (C/N0)43dBHzRange 0 to 99, null when not tracking.
Satellite ID26Channel 3, ID range 1 to 32.
Elevation36degreeElevation of satellite, maximum 90.
Azimuth256degreeAzimuth of satellite, range 0 to 359.
SNR (C/N0)42dBHzRange 0 to 99, null when not tracking.
Satellite ID27Channel 4, ID range 1 to 32.
Elevation27degreeElevation of satellite, maximum 90.
Azimuth138degreeAzimuth of satellite, range 0 to 359.
SNR (C/N0)42dBHzRange 0 to 99, null when not tracking.
Checksum*71
<CR> <LF>Message terminator.
(1) Depending on the number of satellites tracked multiple messages of GSV data may be required.
This message transfersinformation about radio beacon signal-to-noise ratio, signal strength,
frequency, etc.Following isan example.
$GPMSS,55,27,318.0,100,1,*57
The $GPMSS message format isshown below.
FieldExampleUnitNotes
Message ID$GPMSSMSS protocol header.
Signal Strength55dBSS of tracked frequency.
Signal-to-Noise Ratio27dBSNR of tracked frequency.
Beacon Frequency318.0kHzCurrently tracked frequency.
Beacon Bit Rate100Bits per second.
Channel Number
(1)
1
The channel of the beacon being used if a
Checksum*57
<CR> <LF>Message terminator.
(1)
Fields marked in italic red apply only to NMEA version 2.3 (and later) in this NMEA message description.
Message ID$GPRMCRMC protocol header.
UTC Time161229.487hhmmss.sss
Latitude3723.2475ddmm.mmmm
N/S IndicatorNN=north or S=south.
Longitude12158.3416ddmm.mmmm
E/W indicatorWE=east or W=west.
Speed over ground0.13knotSpeed over ground
Course over ground309.62degreeCourse over ground
Date120598ddmmyy, current date.
Magnetic variation
(2)
Mode
Checksum*10
<CR> <LF>Message terminator.
(1) SiRF does not support magnetic declination. All “course over ground” data are geodetic WGS84 directions.
(2)
Fields marked in italic red apply only to NMEA version 2.3 (and later) in this NMEA message description.
This message transfersUTC Time and Date.Following isan example.
$GPZDA,181813,14,10,2003,00,00*4F
The $GPZDA message format isshown below.
FieldExampleUnitNotes
Message ID$GPZDAZDA protocol header.
SG-959 GPS 接收器用户手册中文版 V1.1
UTC Time181813
UTC Day1401 to 31, day of month.
UTC Month1001 to 12.
UTC Year20031980 to 2079.
Local zone hours00Offset from UTC (set to 00).
Local zone minutes00Offset from UTC (set to 00).
Checksum*4F
<CR> <LF>Message terminator.
Either using valid IONO/UTC or estimated
from default leap seconds.