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Page 8 GPS 15 TECHNICAL SPECIFICATIONS
Rev. A P/N 190-00266-00
3 SOFTWARE INTERFACE
The GPS 15 interface protocol design on COM 1 is based on the National Marine Electronics Association’s
NMEA 0183 ASCII interface specification. This standard is fully defined in “NMEA 0183, Version 3.0”
(copies may be obtained from NMEA, www.nmea.org).
The GPS 15 interface protocol, in addition to transmitting navigation information as defined by
NMEA˚0183, transmits additional information using the convention of GARMIN proprietary sentences.
The following sections describe the NMEA 0183 data format of each sentence transmitted and received by
the GPS 15.
3.1
RECEIVED NMEA 0183 SENTENCES
The subsequent paragraphs define the sentences that can be received on the GPS sensors’ COM 1 port. Null
fields in the configuration sentence indicate no change in the particular configuration parameter. All
sentences received by the GPS sensor must be terminated with <CR><LF>, the ASCII characters for
carriage return (0D hexadecimal) and line feed (0A hexadecimal). The checksum *hh is used for parity
checking data and is not required, but is recommended for use in environments containing high
electromagnetic noise. It is generally not required in normal PC environments. When used, the parity bytes
(hh) are the ASCII representation of the exclusive-or (XOR) sum of all the characters between the "$” and
“*” characters, non-inclusive. Sentences may be truncated by <CR><LF> after any data field and valid
fields up to that point will be acted on by the GPS sensor.
3.1.1 Sensor Initialization Information (PGRMI)
The $PGRMI sentence provides information used to initialize the GPS sensor’s set position and time used
for satellite acquisition. Receipt of this sentence by the GPS sensor causes the software to restart the
satellite acquisition process. If there are no errors in the sentence, it will be echoed upon receipt. If an
error is detected, the echoed PGRMI sentence will contain the current default values. Current PGRMI
defaults (with the exception of the Receiver Command, which is a command rather than a mode) can also be
obtained by sending $PGRMIE to the GPS sensor.
$PGRMI,<1>,<2>,<3>,<4>,<5>,<6>,<7>*hh<CR><LF>
<1> Latitude, ddmm.mmm format (leading zeros must be transmitted)
<2> Latitude hemisphere, N or S
<3> Longitude, dddmm.mmm format (leading zeros must be transmitted)
<4> Longitude hemisphere, E or W
<5> Current UTC date, ddmmyy format
<6> Current UTC time, hhmmss format
<7> Receiver Command, A = Auto Locate, R = Unit Reset