ZyCast
SG-289 User’s Manual v1.1
15
Appendix: Software Specifications
NMEA Protocol
The SG-289 interface protocol is based on the National Marine Electronics Association (NMEA)
interface specification, namely, the NMEA 0183 standard. The SG-289 is capable of supporting the
following NMEA message formats specifically developed and defined by SiRF.
NMEA Message Prefix
Format
Direction
$GPGGA
Time, position and fix type data.
Out
$GPGLL
Latitude, longitude, time of position fix and status.
Out
$GPGSA
GNSS DOP and active satellites
Out
$GPGSV
Satellites in view.
Out
$GPMSS
Radio beacon signal-to-noise ratio, signal strength,
frequency, etc.
Out
$GPRMC
Recommended minimum specific GNSS data.
Out
$GPVTG
Speed and course over ground.
Out
$GPZDA
Date and time.
Out
General NMEA Format
The general NMEA format consists of an ASCII string commencing with a ‘$’ 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 digits in each number will vary depending on the number and precision,
hence the record length will vary. Certain fields may be omitted if they are not used, in which case
the field position is reserved using commas to ensure correct interpretation of subsequent fields.
