Garmin 25 Technical Specification

GPS 25 LP SERIES

GPS SENSOR BOARDS

GPS25-LVC, GPS25-LVS, GPS25-HVS

TECHNICAL SPECIFICATION

_______________________________________________________________________ GARMIN· 1200 E. 151st St· Olathe, Kansas 66062· (913)397-8200· (913)397-8282 FAX

form or by any means, electronic or mechanical, including photocopying and recording, for any purpose without the express written permission of GARMIN.

Information in this document is subject to change without notice. GARMIN reserves the right to change or improve their products and to make changes in the content without obligation to notify any person or organization of such changes or improvements.

190-00125-00 Rev. G

Table of Contents

Table of Contents.............................................................................................................i

Section 1 .........................................................................................................................1

Introduction...................................................................................................................1

1.1 Overview...........................................................................................................1

1.2 Naming Conventions ........................................................................................1

1.3 Features ...........................................................................................................2

1.4 Technical Specifications...................................................................................3

1.4.1 Physical Characteristics .............................................................................3

1.4.2 Environmental Characteristics....................................................................3

1.4.3 Electrical Characteristics............................................................................3

1.4.4 Performance...............................................................................................4

1.4.5 Interfaces....................................................................................................4

1.5 Application........................................................................................................5

1.5.1 Application Considerations.........................................................................5

Section 2 .........................................................................................................................7

Operational Characteristics..........................................................................................7

2.1 Self Test ...........................................................................................................7

2.2 Initialization.......................................................................................................7

2.3 Navigation.........................................................................................................8

2.4 Satellite Data Collection...................................................................................8

Section 3 .......................................................................................................................10

Hardware Interface.....................................................................................................10

3.1 Mechanical Dimensions..................................................................................10

3.2 Connector Specifications................................................................................10

3.3 Connector Pin-Out..........................................................................................11

3.4 Antenna Connection.......................................................................................14

Section 4 .......................................................................................................................16

Software Interface ......................................................................................................16

4.1 NMEA Received sentences............................................................................16

4.1.1 Almanac Information (ALM)......................................................................16

4.1.2 Sensor Initialization Information (PGRMI)................................................17

4.1.3 Sensor Configuration Information (PGRMC)............................................17

4.1.4 Additional Sensor Configuration Information (PGRMC1).........................18

4.1.5 Output Sentence Enable/Disable (PGRMO).............................................19

4.1.6 Tune DGPS Beacon Receiver (PSLIB) ....................................................20

4.2 NMEA Transmitted Sentences........................................................................20

4.2.1 Sentence Transmission Rate....................................................................20

4.2.2 Transmitted Time......................................................................................21

4.2.3 Global Positioning System Almanac Data (ALM) .....................................22

4.2.4 Global Positioning System Fix Data (GGA)..............................................22

4.2.5 GPS DOP and Active Satellites (GSA).....................................................23

4.2.6 GPS Satellites in View (GSV)...................................................................23

4.2.7 Recommended Minimum Specific GPS/TRANSIT Data (RMC)................24

4.2.8 Track Made Good and Ground Speed with GPS Talker ID (VTG)...........24

4.2.9 Geographic Position with LORAN Talker ID (LCGLL)..............................24

4.2.10 Track Made Good and Ground Speed with LORAN Talker ID (LCVTG)..25

4.2.11 Estimated Error Information (PGRME) .....................................................25

4.2.12 GPS Fix Data Sentence (PGRMF) ...........................................................25

4.2.13 Sensor Status Information (PGRMT)........................................................26

4.2.14 3D velocity Information (PGRMV).............................................................26

4.2.15 DGPS Beacon Information (PGRMB).......................................................27

4.3 Baud Rate Selection.......................................................................................27

4.4 One-Pulse-Per-Second Output.......................................................................27

4.5 RTCM Received Data.....................................................................................28

Appendix A....................................................................................................................29

Earth Datums..............................................................................................................29

Appendix B....................................................................................................................32

GPS 25LP Connectors...............................................................................................32

Appendix C....................................................................................................................33

GPS 25LP Evaluation Kits..........................................................................................33

Appendix D....................................................................................................................35

Phase Output Data Binary Format .............................................................................35

GARMIN Phase Monitor Program - gps25pm.exe......................................................38

Section 1

Introduction

1.1 Overview

The GARMIN GPS 25LP Series are GPS sensor boards designed for a broad spectrum of OEM (Original Equipment Manufacturer) system applications. The GPS 25LPs will simultaneously track up to twelve satellites providing fast time-to-first-fix, one second navigation updates and low power consumption. Their far-reaching capability meets the sensitivity requirements of land navigation as well as the dynamics requirements of high performance aircraft.

The GPS 25LP design utilizes the latest surface mount technology as well as high-level circuit integration to achieve superior performance while minimizing space and power requirements. All critical components of the system including the RF/IF receiver hardware and the digital baseband are designed and manufactured by GARMIN to ensure the quality and capability of the GPS 25LP sensor board. This hardware capability combined with software intelligence makes the board set easy to integrate and use.

The GPS 25LP is designed to withstand rugged operating conditions, however it should be mounted in an enclosure as part of a larger system designed by an OEM or system integrator. A minimum system must provide the sensor board with conditioned input power and L1 GPS RF signal. The system may communicate with the board set via a choice of two CMOS/TTL or two RS-232 compatible bi-directional communications channels. A highly accurate one-pulse-per-second (PPS) output can be utilized in applications requiring precise timing measurements. An on-board memory rechargeable backup battery allows the sensor board to retain critical data such as satellite orbital parameters, last position, date and time. Non-volatile memory is also used to retain board configuration settings even if backup battery power fails. End user interfaces such as keyboards and displays are added by the application designer.

1.2 Naming Conventions

The GPS 25LP sensors are delineated with a three letter extension to designate the operating voltage range and the serial data voltage specification.

High Voltage - GPS25-HVx designation indicates that the unit will accept a high input voltage. The internal switching regulator will operate from a 6VDC to 40VDC unregulated supply.

Low Voltage - GPS25-LVx designation indicates that the unit is designed to operate from a low voltage 3.6VDC to 6.0VDC supply. Operation at about 4VDC is the most power efficient mode of operation for the GPS25LP sensor. The unit is protected if a high voltage is inadvertently applied to the input.

RS-232 Serial Data - GPS25-xVS designation means that the two bi-directional serial data ports are true RS-232 ports conforming to the RS-232E standard.

CMOS Serial Data - GPS25-xVC designation means that the two bi-directional serial data ports use CMOS output buffers. The inputs buffers will accept either CMOS(TTL) voltage levels or RS-232 voltage levels. This configuration is adequate for communicating directly with serial devices over short cable lengths (less than 20 meters).

1.3 Features

The GPS 25LP sensor boards provide a host of features that make it easy to integrate and use.

1) Full navigation accuracy provided by Standard Positioning Service (SPS)

2) Compact design ideal for applications with minimal space

3) High performance receiver tracks up to 12 satellites while providing fast first fix and low power consumption

4) Differential capability utilizes real-time RTCM corrections producing less than 5 meter position accuracy

5) On-board clock and memory are sustained by a rechargeable memory backup battery which recharges during normal operation or by optional external standby power

6) User initialization is not required.

7) Two communication channels and user selectable baud rates allow maximum interface capability and flexibility. The standard channels are CMOS/TTL levels for the -xVC version or RS-232 for the xVS versions.

8) Highly accurate one-pulse-per-second output for precise timing measurements. The default pulse width is 100 msec, however it is configurable in 20 msec increments from 20 msec to 980 msec.

9) Binary Format Phase Data Output on TXD2

10) Flexible input voltage levels of 3.6Vdc to 6.0Vdc with overvoltage protection in the

-LVx, and 6.0Vdc to 40Vdc in the -HVx versions.

11) Fully shielded construction for maximum EMI and RFI protection

12) FLASH based program memory. New software revisions upgradeable through serial interface

1.4 Technical Specifications

Specifications are subject to change without notice.

1.4.1 Physical Characteristics

1) Single board integrated with complete component shielding

2) Weight: 1.3 ounce [38g]

3) Size: 1.83" (w) x 2.75" (l) x 0.45" (h)

1.4.2 Environmental Characteristics

1) Operating temperature: -30°C to +85°C (board temperature)

2) Storage temperature: -40°C to +90°C

1.4.3 Electrical Characteristics

1) Input voltage: +3.6VDC to 6.0VDC regulated, 150 mVp-p ripple -LVx versions.

+6.0VDC to 40VDC unregulated -HVx version.

2) Input current: 120 mA typical 140 mA max -LVx versions, 20 mA while in power

down. 870mW typical 1000mW max -HVx version, 300uA while in power down.

3) Backup power: 3V Rechargeable Lithium cell battery, up to 6 month charge

4) Auxiliary battery recharge voltage: 4Vdc to 35Vdc at 4mA typical.

5) Receiver sensitivity: -165dBW minimum

1.4.4 Performance

1) Tracks up to 12 satellites (up to 11 with PPS active)

2) Update rate: 1 second

3) Acquisition time

- 15 seconds warm (all data known)

- 45 seconds cold (initial position, time and almanac known, ephemeris unknown)

- 1.5 minutes AutoLocateTM (almanac known, initial position and time unknown)

- 5 minutes search the sky (no data known)

4) Position accuracy:

Differential GPS (DGPS): Less than 5 meters RMS Non-differential GPS: 15 meters RMS (100 meters with Selective Availability on)

5) Velocity accuracy: 0.2 m/s RMS steady state (subject to Selective Availability)

6) Dynamics: 999 knots velocity, 6g dynamics

7) One-pulse-per-second accuracy: ±1 microsecond at rising edge of PPS pulse (subject to Selective Availability)

1.4.5 Interfaces

1) Dual channel CMOS/TTL level (-xVC versions) or RS-232 compatible level (-xVS versions), with user selectable baud rate (300, 600,1200, 2400, 4800, 9600,

19200)

2) NMEA 0183 Version 2.0 ASCII output (GPALM, GPGGA, GPGSA, GPGSV, GPRMC, GPVTG, PGRME, PGRMT, PGRMV, PGRMF, LCGLL, LCVTG)

Inputs

- Initial position, date and time (not required)

- Earth datum and differential mode configuration command, PPS Enable, almanac Outputs

- Position, velocity and time

- Receiver and satellite status

- Differential Reference Station ID and RTCM Data age

- Geometry and error estimates

3) Real-time Differential Correction input (RTCM SC-104 message types 1,2,3 and 9)

4) One-pulse-per-second timing output

5) Optional binary TTL output data format

6) Binary Format Phase Data

1.5 Application

GPS 25LP Series Block Diagram

TYPICAL APPLICATION ARCHITECTURE

1.5.1 Application Considerations

1) The GPS 25LP sensor boards contain a sensitive receiver. Additional electromagnetic shielding may be required to prevent undesirable interference from other nearby circuits.

2) The GPS 25LP sensor boards use approximately 0.5 W to .85 W, depending on supply voltage, and require minimal cooling. Forced air cooling is not

recommended since it may cause rapid temperature changes which may temporarily affect the frequency stability of the internal oscillator.

3) Interruptions in the RF signal can increase acquisition time. Antenna location with clear line-of-sight to all directions in the sky will yield the best performance.

4) The GPGSV sentence contains signal strength information for the visible satellites. Typical values will be between 30 db and 50 db. A majority of values near the lower limit may indicate a marginal RF signal.

Section 2

Operational Characteristics

This section describes the basic operational characteristics of the GPS 25LP sensor boards. Additional information regarding input and output specifications are contained in Section 4.

2.1 Self Test

After input power has been applied to the GPS 25LP sensor boards and periodically thereafter, the units will perform critical self test functions and report the results over the output channel(s). The following tests will be performed:

1) RAM check

2) FLASH test

3) Receiver test

4) Real-time clock test

5) Oscillator check

In addition to the results of the above tests, the board set will report software version information.

2.2 Initialization

After the initial self test is complete, the GPS 25LP will begin the process of satellite acquisition and tracking. The acquisition process is fully automatic and, under normal circumstances, will take approximately 45 seconds to achieve a position fix (15 seconds if ephemeris data is known). After a position fix has been calculated, valid position, velocity and time information will be transmitted over the output channel(s).

Like all GPS receivers, the GPS 25LP utilizes initial data such as last stored position, date and time as well as satellite orbital data to achieve maximum acquisition performance. If significant inaccuracy exists in the initial data, or if the orbital data is obsolete, it may take 1.5 minutes to achieve a navigation solution. The GPS 25LP AutoLocateTM feature is capable of automatically determining a navigation solution without intervention from the host system. However, acquisition performance can be improved if the host system initializes the board set following the occurrence of one or more of the following events:

1) Transportation over distances further than 1500 kilometers

2) Failure of the on-board memory battery

3) Stored date/time off by more than 30 minutes

See Section 4 for more information on initializing the GPS 25LP.

2.3 Navigation

After the acquisition process is complete, the GPS 25LP will begin sending valid navigation information over its output channels. These data include:

1) Latitude/longitude/altitude

2) Velocity

3) Date/time

4) Error estimates

5) Satellite and receiver status

The GPS 25LP sensor boards will select the optimal navigation mode (2D or 3D) based on available satellites and geometry considerations. When navigating in the 2D mode the board set utilizes the last computed altitude or the last altitude supplied by the host system, whichever is newer. The host system must ensure that the altitude used for 2D navigation is accurate since the resulting position error may be as large as the altitude error. See Section 4 for information altitude initialization.

The GPS 25LP will default to automatic differential mode -- “looking” for real-time differential corrections in RTCM SC-104 standard format using message types 1,2,3 or 9 and attempting to apply them to the satellite data in order to produce a differential (DGPS) solution. The host system, at its option, may also command the board set to choose differential only mode. When navigating in the differential only mode, the board set will output a position only when a differential solution is available.

2.4 Satellite Data Collection

The GPS 25LP sensor boards will automatically update satellite orbital data as they operate. The intelligence of the board set combined with its hardware capability allows these data to be collected and stored without intervention from the host system. A few key points should be considered regarding this process:

1) If the sensor board is not operated for a period of six (6) months or more, the unit will “search the sky” in order to collect satellite orbital information. This process is fully automatic and, under normal circumstances, will take 3-4 minutes to achieve

a navigation solution. However, the host system should allow the board set to remain on for at least 12.5 minutes after the first satellite is acquired (see Section 4 for more information on status indications).

2) If the memory backup battery fails, the sensor board will search the sky as described above. The system designer should be aware of the availability of standby power input to the board set to prevent this situation.

3) If the initial data is significantly inaccurate, the board set will perform an operation known as AutoLocateTM. This procedure is fully automatic and, under normal circumstances, will require 1.5 minutes to calculate a navigation solution. AutoLocateTM, unlike search the sky, does not require that the sensor board continue to operate after a fix has been obtained.

Section 3

Hardware Interface

3.1 Mechanical Dimensions

The GPS 25LP sensor board mounts via four #4 or M-3 size screws (see drawing).

3.2 Connector Specifications

The GPS 25LP sensor boards features a single row, right angle, 12-pin male connector. The mating connector is available from JST Corporation (see appendix B).

3.3 Connector Pin-Out

PIN-OUT DIAGRAM

The following is a functional description of each pin of the interface connector. The pins are numbered from left to right as viewed from the connector end of the board with the connector on top.

Pin 1: TXD2 - Second Serial Asynchronous Output. Electrically identical to

TXD1. This output provides phase data (Ver 2.03) see Appendix D

Pin 2: RXD2 - Second Serial Asynchronous Input. Electrically identical to

RXD1. This input may be used to receive serial differential GPS data formatted per “RTCM Recommended Standards For Differential Navstar GPS Service, Version 2.1” (see Section 4 for more details).

Pin 3: PPS - One-Pulse-Per-Second Output. Typical voltage rise and fall times

are 300 nSec. Impedance is 250 ohms. Open circuit output voltage is 0V and Vin. The default format is a 100 millisecond high pulse at a 1Hz rate, the pulse width is programmable from a configuration command in 20msec increments. Rising edge is synchronized to the start of each GPS second. This output will provide a nominal 700 mVp-p signal into a 50 Ohm load. The pulse time measured at the 50% voltage point will be about 50 nSec earlier with a 50 Ohm load than with no load.

Pin 4: TXD1 - First Serial Asynchronous Output. CMOS/TTL output levels vary

between 0V and Vin in the -LVC version. In the -LVS and -HVS versions a RS-232 compatible output driver is available. This output normally provides serial data which is formatted per “NMEA 0183, Version

2.0”. Switchable to 300, 600, 1200, 2400, 4800, 9600 or 19200 BAUD. The default BAUD is 4800. This output data functions in parallel with pin

12.

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