190-00879-08
GPS 18x Technical Specifications
Rev. B
Page 15
4.2
TRANSMITTED NMEA 0183 SENTENCES
The subsequent paragraphs define the sentences that can be transmitted by the GPS 18x PC and LVC.
4.2.1
Sentence Transmission Rate
Sentences are transmitted with respect to the user selected baud rate.
The GPS sensor will transmit each sentence (except where noted in particular transmitted sentence descriptions) at a
periodic rate based on the user selected baud rate and user selected output sentences. The GPS sensor will transmit
the selected sentences contiguously. The length of the transmission can be determined by the following equation and
Tables 2 and 3:
total
characters
to
be
transmitted
length of transmission = ---------------------------------------------
characters
transmitted
per
second
Sentence Output
by
Default? Maximum
Characters
GPRMC
74
GPGGA
82
GPGSA
66
GPGSV
(PC and LVC only)
70
PGRME
35
GPGLL
44
GPVTG
(18x-5Hz)
42
PGRMV
32
PGRMF
82
PGRMB
40
PGRMM
PGRMT
Once per minute
50
Table 2: NMEA 0183 Output Sentence Order and Size
Baud Characters
per
Second
4800 480
9600 960
19200 1920
38400 3840
Table 3: Characters per Second for Available Baud Rates
The maximum number of fields allowed in a single sentence is 82 characters including delimiters. Values in the
table include the sentence start delimiter character “$” and the termination delimiter <CR><LF>. For the GPS 18x
PC and LVC, the factory set defaults result in a once per second transmission at the NMEA 0183 specification
transmission rate of 4800 baud. For the GPS 18x-5Hz, the factory set defaults will result in a five times per second
transmission at 19200 baud.
For the GPS 18x LVC: Regardless of the selected baud rate, the information transmitted by the GPS sensor is
referenced to the one-pulse-per-second output pulse immediately preceding the GPRMC sentence, or whichever
sentence is output first in the burst (see Table 2 above).
For the GPS 18x-5Hz: Regardless of the selected baud rate, the information transmitted by the GPS sensor is
referenced to the preceding five-times-per-second output pulse.
The GPS 18x USB can use Spanner (an application that can provide NMEA output via a virtual COM port) to
receive the same default NMEA sentences as the GPS 18x PC and LVC at a rate of once per second. Spanner is
available for free on the Garmin web site. To download the software, start at
18x USB, and then select
Updates & Downloads
.
