Linx Technologies RXM-GPS-F4 - Manual (Page 5)

– – – – 4 5
GPIOD 1
GPIOE 2
1PPS 3
TX 4
RX 5
GND 21
GPIOC 6
P1 7
/RESET 8
RFPWRUP 9
ON_OFF 10
GND 20
RFIN 19
GND 18
NC 17
NC 16
GND 22
GPIOB 15
GPIOA 14
G1 13
VCC 12
P2 11
Pin Assignments
Pin Descriptions
Pin Descriptions
Pin Number Name I/O Description
1 GPIOD I/O General Purpose I/O. 3.6V tolerant.
2 GPIOE I/O General Purpose I/O. 3.6V tolerant.
3 1PPS O 1 Pulse Per Second. 1.8V level.
4 TX O Serial output (default NMEA)
5 RX I Serial input (default NMEA). 3.6V tolerant.
6 GPIOC I/O General Purpose I/O. 3.6V tolerant.
7, 11 P1, P2 I Pull to 1.8V VCC through 2.2k resistors.
8 /RESET I
Reset Input. Active low with an internal pull-up.
Internal reset is preferred; external reset will clear
all RAM. 3.6V tolerant.
9 RFPWRUP O Power State Indicator
10 ON_OFF I
Power Control Pin. Internal 10k pull-down
resistor. 3.6V tolerant.
12 VCC P Supply Voltage
13 G1 I Pull to GND through a 100k resistor.
14 GPIOA I/O General Purpose I/O. 3.6V tolerant.
15 GPIOB I/O General Purpose I/O. 3.6V tolerant.
16, 17 NC − No electrical connection.
18, 20, 21, 22 GND P Ground
19 RFIN I GPS RF signal input
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 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.
Client Generated Extended Ephemeris (CGEE)
CGEE is a type of assisted GPS (AGPS) where the receiver uses the
ephemeris data broadcast by the satellites to calculate models of each
visible satellite’s future location. This allows the receiver to store up to 3
days worth of ephemeris data and results in faster TTFF.
Figure 5: F4 Series GPS Receiver Pin Assignments (Top View)
Figure 6: F4 Series GPS Receiver Pin Descriptions