Linx Technologies RXM-GPS-SG - Manual (Page 3)

PIN ASSIGNMENTS
NC 1
NC 2
1PPS 3
TXA 4
RXA 5
GND 21
GPIO10 6
LCKIND 7
GPIO1 8
RFPWRUP 9
ON_OFF 10
GND 20
RFIN 19
GND 18
VOUT 17
NC 16
GND 22
GPIO13 15
GPIO15 14
GPIO14 13
VCC 12
VBACKUP 11
Figure 2: SG Series Receiver Pinout (Top View)
Pin # Name I/O Description
1, 2, 16 NC – No Connect. No electrical connection.
3 1PPS O Pulse per second (1uS pulse)
4 TXA O Serial output for channel A (default NMEA)
5 RXA I Serial input for channel A (default NMEA)
6 GPIO10 I/O General Purpose I/O
7 LCKIND O Lock Indicator
8 GPIO1 I/O General Purpose I/O, 100k Ω pull down
9 RFPWRUP O Indicate power state
10 ON_OFF I
Edge triggered soft on/off request. Should only be
used to wake up the module when the RFPWRUP line
is low.
11 VBACKUP P
Backup battery supply voltage. This line must be
powered to enable the module.
12 VCC P Supply Voltage
13 GPIO14 I/O General Purpose I/O, 100k Ω pull up
14 GPIO15 I/O General Purpose I/O, 100k Ω pull up
15 GPIO13 I/O General Purpose I/O
17 VOUT P 2.85V Linear regulator power output
18,20-22 GND P Ground
19 RFIN I GPS RF signal input
PIN DESCRIPTIONS
A BRIEF OVERVIEW OF GPS
The Global Positioning System (GPS) is a U.S.-owned utility that freely and
continuously provides positioning, navigation, and timing (PNT) information.
Originally created by the U.S. Department of Defense for military applications,
the system was made available without charge to civilians in the early 1980s.
The global positioning system consists of a nominal constellation of 24 satellites
orbiting the earth at about 12,000 nautical miles in height. The pattern and
spacing of the satellites allow at least four to be visible above the horizon from
any point on the Earth. Each satellite transmits low power radio signals which
contain three different bits of information; a pseudorandom code identifying the
satellite, ephemeris data which contains the current date and time as well as the
satellite’s health, and the almanac data which tells where each satellite should
be at any time throughout the day.
A GPS receiver such as the Linx SG Series GPS module receives and times the
signals sent by multiple satellites and calculates the distance to each satellite. If
the position of each satellite is known, the receiver can use triangulation to
determine its position anywhere on the earth. The receiver uses four satellites to
solve for four unknowns; latitude, longitude, altitude, and time. If any of these
factors is already known to the system, an accurate position (Fix) can be
obtained with fewer satellites in view. Tracking more satellites improves
calculation accuracy. In essence, the GPS system provides a unique address for
every square meter on the planet.
A faster Time To First Fix (TTFF) is also possible if the satellite information is
already stored in the receiver. If the receiver knows some of this information,
then it can accurately predict its position before acquiring an updated position fix.
For example, aircraft or marine navigation equipment may have other means of
determining altitude, so the GPS receiver would only have to lock on to three
satellites and calculate three equations to provide the first position fix after
power-up.
TTFF is often broken down into three parts:
Cold: A cold start is when the receiver has no accurate knowledge of its position
or time. This happens when the receiver’s internal Real Time Clock (RTC) has
not been running or it has no valid ephemeris or almanac data. In a cold start,
the receiver takes 35 to 40 seconds to acquire its position. If new almanac data
is required, this may take up to 15 minutes (see page 9 for more details).
Warm or Normal: A typical warm start is when the receiver has valid almanac
and time data and has not significantly moved since its last valid position
calculation. This happens when the receiver has been shut down for more than
2 hours, but still has its last position, time, and almanac saved in memory, and
its RTC has been running. The receiver can predict the location of the current
visible satellites and its location; however, it needs to wait for an ephemeris
broadcast (every 30 seconds) before it can accurately calculate its position.
Hot or Standby: A hot start is when the receiver has valid ephemeris, time, and
almanac data. This happens when the receiver has been shut down for less than
2 hours and has the necessary data stored in memory with the RTC running. In
a hot start, the receiver takes 1 to 2 seconds to acquire its position. The time to
calculate a fix in this state is sometimes referred to as Time to Subsequent Fix
or TTSF.
Page 4 Page 5