–

–

–

–

4

5

NC

1

NC

2

1PPS

3

TX

4

RX

5

GND

21

NC

6

1PPS

7

/RESET

8

RFPWRUP

9

ON_OFF

10

GND

20

RFIN

19

GND

18

VOUT

17

NC

16

GND

22

NC

15

NC

14

NC

13

VCC

12

VBACKUP

11

Figure 5: R4 Series GPS Receiver Pinout (Top View)

Figure 6: R4 Series GPS Receiver Pin Descriptions

Pin Assignments

Pin Descriptions

Pin Descriptions

Pin Number

Name

I/O Description

1, 2, 6, 13,

14, 15, 16

NC

−

No electrical connection.

3, 7

1PPS

O

1 Pulse Per Second. 1.8V level.

4

TX

O

Serial output (default NMEA)

5

RX

I

Serial input (default NMEA)

8

/RESET

I

Reset input, active low. The module has an

internal power-on reset circuit so this pin can be

left floating

9

RFPWRUP

O

Power State Indicator. 1.8V level.

10

ON_OFF

I

Power Control Pin. If this pin is not used, leave it

floating.

11

VBACKUP

P

Backup battery supply voltage. This line must be

powered to enable the module.

12

VCC

P

Supply Voltage

18, 20, 21, 22

GND

P

Ground

17

VOUT

O

VCC voltage to supply an active antenna.

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.