GPS 15 Technical Specifications (P/N 190-00266-00)
Rev. B
Page 10
4
GPS 15 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 2.20
.
Copies may be obtained from NMEA,
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. These
proprietary sentences begin with the characters, “$PGRM”, instead of the characters “$G” that are typical
of the standard NMEA 0183 sentences. The characters “$P” indicate that the sentence is a proprietary
implementation and the characters and “GRM” indicate that it is Garmin’s proprietary sentence. The letter
(or letters) that follow the characters “$PGRM” uniquely identifies that particular Garmin proprietary
sentence.
The following sections describe the NMEA 0183 data format of each sentence transmitted and received by
the GPS 15.
4.1
RECEIVED NMEA 0183 SENTENCES
The following paragraphs define the sentences that can be received on the GPS sensors’ 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), respectively. 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 upper and lower nibbles of the exclusive-or (XOR) sum of all the
characters between the “$” and “*” characters, non-inclusive. The hex representation must be a capital
letter, such as 3D instead of 3d. Sentences may be truncated by <CR><LF> after any data field and valid
fields up to that point will be acted on by the sensor.
4.1.1
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
