GPS 18 TECHNICAL SPECIFICATIONS
Garmin International, Inc. 1200 E. 151st Street Olathe, KS 66062 USA 190-00307-00, Revision D June 2005
GPS 18 Technical Specifications (190-00307-00)

Rev. D

Copyright 20042005 Garmin Ltd. or its subsidiaries All Rights Reserved Except as expressly provided below, no part of this manual may be reproduced, copied, transmitted, disseminated, downloaded or stored in any storage medium, for any purpose without the express prior written consent of Garmin. Garmin hereby grants permission to download a single copy of this manual and of any revision to this manual onto a hard drive or other electronic storage medium to be viewed and to print one copy of this manual or of any revision hereto, provided that such electronic or printed copy of this manual or revision must contain the complete text of this copyright notice and provided further that any unauthorized commercial distribution of this manual or any revision hereto is strictly prohibited. Information in this document is subject to change without notice. Garmin reserves the right to change or improve its products and to make changes in the content without obligation to notify any person or organization of such changes or improvements. Garmin International, Inc. 1200 East 151st Street, Olathe, Kansas 66062, U.S.A. Tel. 913/397.8200 or 800/800.1020 Fax 913/397.8282 Garmin (Europe) Ltd. Unit 5, The Quadrangle, Abbey Park Industrial Estate, Romsey, SO51 9DL, U.K. Tel. 44/0870.8501241 Fax 44/0870.8501251 Garmin Corporation No. 68, Jangshu 2nd Road, Shijr, Taipei County, Taiwan Tel. 886/2.2642.9199 Fax 886/2.2642.9099 Web site address: www.garmin.com RECORD OF REVISIONS

Revision A B C D

Revision Date 4/5/04 6/7/04 5/24/05 6/6/05
Description Initial Release Revise to include PGRMO Add GPS 18 LVC-5m and GPS 18-5Hz Add 38400 baud to field 10 of PGRMC sentence

ECO # -31511

GPS 18 Technical Specifications (190-00307-00) Page i
TABLE OF CONTENTS 1 Introduction....1
1.1 Cautions.....1 1.2 Limited Warranty....2 1.3 Features.....3 1.4 GPS 18 Series....4
1.4.1 1.4.2 1.4.3 1.5.1 GPS 18 USB.... 4 GPS 18 PC..... 4 GPS 18 LVC, GPS 18 LVC-5m, and GPS 18-5Hz... 4 Physical Characteristics.... 5 1.5.1.1 Size.... 5 1.5.1.2 Weight.... 5 1.5.1.3 Color..... 5 1.5.1.4 Case Material.... 5 1.5.1.5 Cable Length.... 5 Electrical Characteristics.... 5 1.5.2.1 Input Voltage.... 5 1.5.2.2 Input Current.... 5 1.5.2.3 CMOS Serial Output Levels.... 5 1.5.2.4 GPS Receiver Sensitivity... 6 Environmental Characteristics.... 6 GPS Performance.... 6 1.5.4.1 Receiver..... 6 1.5.4.2 Acquisition Times.... 6 1.5.4.3 Update Rate.... 6 1.5.4.4 Accuracy..... 6 Interfaces.... 7 1.5.5.1 GPS 18 Electrical Characteristics... 7 1.5.5.2 Garmin Interface and Garmin USB Protocol... 7 1.5.5.3 GPS 18 PC, GPS 18 LVC, & GPS 18-5Hz Protocols... 7 1.5.5.4 Measurement Pulse Output (GPS 18 LVC & GPS 18-5Hz only).. 7
1.5 Technical Specifications....5

1.5.3 1.5.4

GPS 18 LVC & GPS 18-5Hz Wiring and Pinouts..8
2.1 GPS 18 LVC & GPS 18-5Hz Pinout....8 2.2 GPS 18 LVC & GPS 18-5Hz Wiring Diagrams...8
Mechanical Characteristics & Mounting...10 GPS 18 PC, GPS 18 LVC, & GPS 18-5Hz Software Interface..12
4.1 Received NMEA 0183 Sentences....12
4.1.1 4.1.2 4.1.3 4.1.4 4.1.5 4.2.1 4.2.2 4.2.3 4.2.4 4.2.5 4.2.6 4.2.7 4.2.8 Almanac Information (ALM)....12 Sensor Initialization Information (PGRMI)...13 Sensor Configuration Information (PGRMC)....13 Additional Sensor Configuration Information (PGRMC1)..14 Output Sentence Enable/Disable (PGRMO)...14 Sentence Transmission Rate....15 Transmitted Time.....16 Global Positioning System Almanac Data (ALM)...16 Global Positioning System Fix Data (GGA)...17 GPS DOP and Active Satellites (GSA)....17 GPS Satellites in View (GSV)....17 Recommended Minimum Specific GPS/TRANSIT Data (RMC)..18 Track Made Good and Ground Speed (VTG)....18
4.2 Transmitted NMEA 0183 Sentences....15
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4.2.9 4.2.10 4.2.11 4.2.12 4.2.13 4.2.14
Geographic Position (GLL)....18 Estimated Error Information (PGRME)...19 GPS Fix Data Sentence (PGRMF)....19 Sensor Status Information (PGRMT)....19 3D Velocity Information (PGRMV)....19 DGPS Beacon Information (PGRMB)...20
4.3 Baud Rate Selection....20 4.4 Measurement Pulse Output (GPS 18 LVC & 18-5Hz only)...20
4.4.1 4.4.2 One-Pulse-Per-Second (PPS) Output (GPS 18 LVC Only)..20 Five-Pulse-Per-Second Output (GPS 18-5Hz Only)...20
Appendix A: Earth Datum List...21 Appendix B: Binary Phase Output Format..24 Appendix C: Changing the Baud Rate in Garmin Mode..29 Appendix D: GPS 18 PC/ LVC/18-5Hz & Windows Serial Mouse Issue.30 Appendix E: Sensor Configuration Software...32

Downloading the Sensor Configuration Software....32 Selecting a Model.....32 Connecting to the Sensor....32 File Menu.....33 Comm Menu.....33 Config Menu.....33 View Menu.....34 Help Menu.....34
LIST OF TABLES AND FIGURES
Table 1: GPS 18 LVC & GPS 18-5Hz Wire Pinout.... 8 Figure 1: Computer Serial Port Interconnection... 8 Figure 2. PDA Serial Port Interconnection.... 9 Figure 3. Basic NMEA Device Interconnection... 9 Figure 4a. GPS 18 Bottom Case Dimensions, Under Mold... 10 Figure 4b. GPS 18 Bottom Case, Outside of Casing... 10 Figure 5. GPS 18 Suction Cup Mount Center Hole Dimensions... 11 Figure 6. GPS 18 Flush Mount Dimensions.... 11 Figure 7. GPS 18 Flush Mount Center Hole Dimensions.... 11 Table 2: NMEA 0183 Output Sentence Order and Size... 15 Table 3: Characters per Second for Available Baud Rates... 15
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INTRODUCTION CAUTIONS CAUTION
The GPS system is operated by the government of the United States, which is solely responsible for its accuracy and maintenance. Although the GPS 18 is a precision electronic NAVigation AID (NAVAID), any NAVAID can be misused or misinterpreted, and therefore become unsafe. Use these products at your own risk. To reduce the risk, carefully review and understand all aspects of these Technical Specifications before using the GPS 18. When in actual use, carefully compare indications from the GPS to all available navigation sources including the information from other NAVAIDs, visual sightings, charts, etc. For safety, always resolve any discrepancies before continuing navigation.

FCC Compliance

The GPS 18 complies with Part 15 of the FCC interference limits for Class B digital devices FOR HOME OR OFFICE USE. These limits are designed to provide reasonable protection against harmful interference in a residential installation, and are more stringent than outdoor requirements. Operation of this device is subject to the following conditions: (1) This device may not cause harmful interference, and (2) this device must accept any interference received, including interference that may cause undesired operation. This equipment generates, uses and can radiate radio frequency energy and, if not installed and used in accordance with the instructions, may cause harmful interference to radio communications. However, there is no guarantee that interference will not occur in a particular installation. If this equipment does cause harmful interference to radio or television reception, which can be determined by turning the equipment off and on, the user is encouraged to try to correct the interference by one or more of the following measures: Reorient or relocate the receiving antenna. Increase the separation between the equipment and receiver. Connect the equipment into an outlet on a circuit different from that to which the receiver is connected. Consult the dealer or an experienced radio/TV technician for help.

Physical Characteristics

1.5.1.1 Size 61 mm in diameter and 19.5 mm in height 1.5.1.2 Weight GPS 18 unit only (no cable): 1.9 oz (53.9 g) GPS 18 USB: 3.5 oz (100.4 g) GPS 18 PC: 6.5 oz (184.6 g) GPS 18 LVC (3 meter cable): 3.9 oz (110.6 g) GPS 18 LVC-5m (5 meter cable): 5.7 oz (161.6 g) GPS 18-5Hz (5 meter cable): 5.7 oz (161.6 g)
1.5.1.3 Color Black 1.5.1.4 Case Material Polycarbonate thermoplastic that is waterproof to IEC 60529 IPX7 level (immersion in 1 meter of water for 30 minutes) 1.5.1.5 Cable Length GPS 18 USB: 2 meter GPS 18 PC: 2 meter GPS 18 LVC: 3 meter (Garmin Part Number 010-00321-05) GPS 18 LVC-5m: 5 meter (Garmin Part Number 010-00321-06) GPS 18-5Hz: 5 meter
Electrical Characteristics
1.5.2.1 Input Voltage GPS 18 USB: 4.45.5 V GPS 18 PC: 830 V (Automotive supply from cigarette lighter jack)
GPS 18 LVC: 4.05.5 V GPS 18-5Hz: 4.05.5 V
1.5.2.2 Input Current GPS 18 USB: 55 mA @ 5.0 V GPS 18 PC: 50 mA @ 13.8 V
GPS 18 LVC: 60 mA @ 5.0 V GPS 18-5Hz: 65 mA @ 5.0 V
1.5.2.3 CMOS Serial Output Levels GPS 18 PC: 0 V to 5 V (Asynchronous Serial, TIA-232-F (RS-232) Compatible Polarity) GPS 18 LVC and GPS 18-5Hz: 0 V to Vin, between 4 and 5.5 V (Asynchronous Serial, TIA-232-F (RS-232) Compatible Polarity)
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1.5.2.4 GPS Receiver Sensitivity -165 dBW minimum
Environmental Characteristics

-40C to +90C

Operating Temperature: -30C to +80C Storage Temperature:

GPS Performance

1.5.4.1 Receiver WAAS enabled; 12 parallel channel GPS receiver continuously tracks and uses up to 12 satellites (up to 11 with Measurement Pulse Output active) to compute and update your position. 1.5.4.2 Acquisition Times Reacquisition: Less than 2 seconds Warm: Cold: Approx. 15 seconds (all data known) Approx. 45 seconds (initial position, time, and almanac known; ephemeris unknown)
AutoLocateTM: 5 minutes (almanac known; initial position and time unknown) SkySearch: 5 minutes (no data known)
1.5.4.3 Update Rate GPS 18 USB, PC, and LVC: 1 record per second GPS 18-5Hz: 5 records per second
1.5.4.4 Accuracy GPS Standard Positioning Service (SPS) Position: < 15 meters, 95% typical Velocity: 0.1 knot RMS steady state WAAS Position: < 3 meters, 95% typical Velocity: 0.1 knot RMS steady state Measurement Pulse Output Time: 1 microsecond at rising edge of the pulse Dynamics: 999 knots velocity (only limited at altitude greater than 60,000 feet), 6g dynamics

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GPS 18 LVC & GPS 18-5Hz WIRING AND PINOUTS
The GPS 18 LVC/18-5Hz interfaces to a serial port. The unit accepts TIA-232-F (RS-232) level inputs and transmits voltage levels from ground to the input voltage, TIA-232-F (RS-232) polarity. The GPS 18 LVC/18-5Hz wires are terminated with a six-wire connector that is used by Garmin for testing purposes. You can remove this connector without voiding your warranty (see Section 1.2 Limited Warranty).
GPS 18 LVC & GPS 18-5Hz PINOUT
GPS 18 Pin # Color Signal Name Wire Gauge Yellow Measurement Pulse Output 28 Red Vin 26 Black Ground 28 White Transmit Data 28 Black Ground 26 Green Receive Data 28 Table 1: GPS 18 LVC & GPS 18-5Hz Wire Pinout
GPS 18 LVC & GPS 18-5Hz WIRING DIAGRAMS
Figure 1: Computer Serial Port Interconnection
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Figure 2. PDA Serial Port Interconnection
Figure 3. Basic NMEA Device Interconnection
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MECHANICAL CHARACTERISTICS & MOUNTING
The central threaded recess accepts a metric M3 threaded bolt. The recess is approximately 4 mm deep (4.32 +/- 0.08 mm). The following drawings show example geometries for mounting hardware in case you wish to design your own custom mount. Figure 5 shows mounting geometry for a mount formed from steel sheet metal that is 1.15 mm thick. Figure 7 shows similar mounting geometry for mount formed from aluminum sheet metal that is 1.25 mm thick. Use caution when tightening the mounting bolt. Tightening the mounting bolt can cause the mount to pull tight directly against the metal insert, not against the plastic housing, which would tend to pull the insert out of the plastic. Figure 6 shows the dimensions of our GPS 18 Flush Mount, part number 010-10453-00.
Figure 4a. GPS 18 Bottom Case Dimensions, Under Mold
Figure 4b. GPS 18 Bottom Case, Outside of Casing
GPS 18 Technical Specifications (190-00307-00) Page 10
Figure 5. GPS 18 Suction Cup Mount Center Hole Dimensions
Figure 6. GPS 18 Flush Mount Dimensions
Figure 7. GPS 18 Flush Mount Center Hole Dimensions GPS 18 Technical Specifications (190-00307-00) Page 11 Rev. D
GPS 18 PC, GPS 18 LVC, & GPS 18-5Hz SOFTWARE INTERFACE
The interface protocol design of the GPS 18 PC, LVC, and GPS 18-5Hz products is based on the National Marine Electronics Associations NMEA 0183 ASCII interface specification. This standard is fully defined in NMEA 0183, Version 2.30. Copies may be obtained from NMEA, www.nmea.org. In addition to the standard NMEA 0183 sentences, the GPS 18 PC, LVC, and GPS 18-5Hz may also be configured to transmit information over their serial interface using NMEA 0183 compliant Garmin proprietary sentences. These proprietary sentences begin with the characters, $PGRM, instead of the characters $G that are typical of the standard NMEA 0183 sentences. The characters $P indicate that the sentence is a proprietary implementation and the characters and GRM indicate that it is Garmins proprietary sentence. The letter (or letters) that follow the characters $PGRM uniquely identifies that particular Garmin proprietary sentence. It is also possible to configure the GPS 18 PC, LVC, and GPS 18-5Hz to transmit binary phase data information over their serial interface. See Appendix B: Binary Phase Output Format for details. The GPS 18 USB does not transmit NMEA sentences: It transmits using the Garmin USB interface. The Garmin USB interface is discussed in the Garmin Device Interface Specification located on the Garmin Web site at: http://www.garmin.com/support/commProtocol.html. You can configure the GPS 18 USB to transmit binary phase data information over the USB interface. Refer to Appendix B: Binary Phase Output Format. The following sections describe the NMEA 0183 data format of each sentence transmitted and received by the GPS 18 PC, LVC, and GPS 18-5Hz products.

RECEIVED NMEA 0183 SENTENCES
The following paragraphs define the sentences that can be received on the GPS sensors port. Null fields in the configuration sentence indicate no change in the particular configuration parameter. All sentences received by the GPS sensor must be terminated with <CR><LF>, the ASCII characters for carriage return (0D hexadecimal) and line feed (0A hexadecimal). The checksum *hh is used for parity checking data and is not required, but is recommended for use in environments containing high electromagnetic noise. It is generally not required in normal PC environments. When used, the parity bytes (hh) are the ASCII representation of the exclusive-or (XOR) sum of all the characters between the $ and * characters, noninclusive. The hex representation must be a capital letter, such as 3D instead of 3d. Sentences may be truncated by <CR><LF> after any data field and valid fields up to that point will be acted on by the sensor.
Almanac Information (ALM)
The $GPALM sentence can be used to initialize the GPS sensors stored almanac information in the unlikely event of non-volatile memory loss or after storing longer than six months without tracking GPS satellites. $GPALM,<1>,<2>,<3>,<4>,<5>,<6>,<7>,<8>,<9>,<10>,<11>,<12>,<13>,<14>,<15>*hh<CR><LF> <1> <2> <3> <4> <5> <6> <7> <8> <9> <10> <11> <12> <13> <14> <15> Total number of ALM sentences to be transmitted by the GPS sensor during almanac download. This field can be null or any number when sending almanac to the GPS sensor. Number of current ALM sentence. This field can be null or any number when sending almanac to the GPS sensor. Satellite PRN number, 01 to 32 GPS week number SV health, bits 1724 of each almanac page Eccentricity Almanac reference time Inclination angle Rate of right ascension Root of semi major axis Omega, argument of perigee Longitude of ascension node Mean anomaly af0 clock parameter af1 clock parameter Rev. D Page 12
Sensor Initialization Information (PGRMI)
The $PGRMI sentence provides information used to initialize the GPS sensors set position and time used for satellite acquisition. Receipt of this sentence by the GPS sensor causes the software to restart the satellite acquisition process. If there are no errors in the sentence, it will be echoed upon receipt. If an error is detected, the echoed PGRMI sentence will contain the current default values. Current PGRMI defaults (with the exception of the Receiver Command, which is a command rather than a mode) can also be obtained by sending $PGRMIE to the GPS sensor. $PGRMI,<1>,<2>,<3>,<4>,<5>,<6>,<7>*hh<CR><LF> <1> <2> <3> <4> <5> <6> <7> Latitude, ddmm.mmm format for GPS 18 PC/LVC; ddmm.mmmmm format for GPS 185Hz (leading zeros must be transmitted) Latitude hemisphere, N or S Longitude, ddmm.mmm format for GPS 18 PC/LVC; ddmm.mmmmm format for GPS 185Hz (leading zeros must be transmitted) Longitude hemisphere, E or W Current UTC date, ddmmyy format Current UTC time, hhmmss format for GPS 18 PC/LVC; hhmmss.s format for GPS 18-5Hz Receiver Command, A = Auto Locate, R = Unit Reset

Sensor Configuration Information (PGRMC)
The $PGRMC sentence provides information used to configure the GPS sensors operation. Configuration parameters are stored in non-volatile memory and retained between power cycles. The GPS sensor will echo this sentence upon its receipt if no errors are detected. If an error is detected, the echoed PGRMC sentence will contain the current default values. Current default values can also be obtained by sending $PGRMCE to the GPS sensor. $PGRMC,<1>,<2>,<3>,<4>,<5>,<6>,<7>,<8>,<9>,<10>,<11>,<12>,<13>,<14>*hh<CR><LF> Fix mode, A = automatic, 2 = 2D exclusively (host system must supply altitude), 3 = 3D exclusively <2> Altitude above/below mean sea level, -1500.0 to 18000.0 meters <3> Earth datum index. If the user datum index (96) is specified, fields <4> through <8> must contain valid values. Otherwise, fields <4> through <8> must be null. Refer to Appendix A: Earth Datum List for a list of earth datum and the corresponding earth datum index. <4> User earth datum semi-major axis, 6360000.000 to 6380000.000 meters (.001 meters resolution) <5> User earth datum inverse flattening factor, 285.0 to 310.0 (10-9 resolution) <6> User earth datum delta x earth centered coordinate, -5000.0 to 5000.0 meters (1 meter resolution) <7> User earth datum delta y earth centered coordinate, -5000.0 to 5000.0 meters (1 meter resolution) <8> User earth datum delta z earth centered coordinate, -5000.0 to 5000.0 meters (1 meter resolution) <9> Differential mode, A = automatic (output DGPS data when available, non-DGPS otherwise), D = differential exclusively (output only differential fixes) <10> NMEA 0183 Baud rate, 1 = 1200, 2 = 2400, 3 = 4800, 4 = 9600, 5 = 19200, 6 = 300, 7 = 600, 8 = 38400 (for GPS 18-5Hz only) <11> Velocity filter, 0 = No filter, 1 = Automatic filter, 2255 = Filter time constant (for example, 10 = 10 second filter) <12> Measurement Pulse Output, 1 = Disabled, 2 = Enabled <13> Measurement Pulse Output pulse length, (n+1)*20 ms For 18 LVC/PC n = 0 through 48 (max. 980 ms) For GPS 18-5Hz n = 0 through 8 (max. 180 ms) Example: n = 4 corresponds to a 100 ms wide pulse <14> Dead reckoning valid time 1 to 30 sec. for the GPS 18 PC/LVC or 0.2 to 30.0 sec. for the GPS 18-5Hz All configuration changes take effect after receipt of a valid value except baud rate and Measurement Pulse Output mode. Baud rate and Measurement Pulse Output mode changes take effect on the next power cycle or an external reset event. <1>

Sentence Output by Default? Maximum Characters GPRMC 74 GPGGA 82 GPGSA 66 GPGSV (PC and LVC only) 70 PGRME (PC and LVC only) 35 GPGLL 44 GPVTG (18-5Hz only) 42 PGRMV 32 PGRMF 82 PGRMB (PC and LVC only) 40 PGRMT Once per minute 50 Table 2: NMEA 0183 Output Sentence Order and Size Baud Characters per Second 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 18 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 18-5Hz, the factory set defaults will result in a five times per second transmission at 19200 baud. For the GPS 18 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 18-5Hz: Regardless of the selected baud rate, the information transmitted by the GPS sensor is referenced to the preceding five times per second output pulse.
GPS 18 Technical Specifications (190-00307-00) Page 15

Transmitted Time

The GPS sensor outputs UTC (Coordinated Universal Time) date and time of day in the transmitted sentences. Before the initial position fix, the on-board clock provides the date and time of day. After the initial position fix, the date and time of day are calculated using GPS satellite information and are synchronized with the measurement pulse output. The GPS 18-5Hz outputs a UTC with a tenths-of-a-second precision: 123456.8, for example. The GPS sensor uses information obtained from the GPS satellites to add or delete UTC leap seconds and correct the transmitted date and time of day. The transmitted date and time of day for leap second correction follow the guidelines in National Institute of Standards and Technology Special Publication 432 (Revised 1990) (for sale by the Superintendent of Documents, U.S. Government Printing Office, Washington, D.C., 20402, U.S.A.). When a positive leap second is required, one second is inserted at the beginning of the first hour (0h 0m 0s) of the day that the positive leap is occurring. The minute containing the leap second is 61 seconds long. The GPS sensor would have transmitted this information for the leap second added December 31, 1998 as follows: $GPRMC,235959,A,3851.3651,N,09447.9382,W,000.0,221.9,071103,003.3,E*69 $GPRMC,000000,A,3851.3651,N,09447.9382,W,000.0,221.9,081103,003.3,E*67 $GPRMC,000000,A,3851.3651,N,09447.9382,W,000.0,221.9,081103,003.3,E*67 $GPRMC,000001,A,3851.3651,N,09447.9382,W,000.0,221.9,081103,003.3,E*66 If a negative leap second should be required, one second will be deleted at the end of some UTC month. The minute containing the leap second will be only 59 seconds long. In this case, the GPS sensor will not transmit the time of day 0h 0m 0s (the zero second) for the day from which the leap second is removed. $GPRMC,235959,A,3851.3650,N,09447.9373,W,000.0,000.0,111103,003.3,E*69 $GPRMC,000001,A,3851.3650,N,09447.9373,W,000.0,000.0,121103,003.3,E*6A $GPRMC,000002,A,3851.3650,N,09447.9373,W,000.0,000.0,121103,003.3,E*69

Five-Pulse-Per-Second Output (GPS 18-5Hz Only)
The highly accurate five-pulse-per-second output is provided for applications requiring precise timing measurements. After the initial position fix has been calculated, the GPS 18-5Hz generates the pulse signal, which continues until power down. The rising edge of the signal is aligned to the start of each GPS second within 1 s for all conditions in which the receiver has reported a valid and accurate position for at least the previous 4 seconds. The NMEA 0183 sentences that follow each rising edge of the Measurement Pulse Output signal tell when and where you were at that previous rising edge of the Measurement Pulse Output signal, beginning with the GPRMC sentence as the lead sentence in any particular NMEA 0183 record. Regardless of the selected baud rate, the information transmitted by the GPS 18-5Hz is referenced to the preceding five times per-second output pulse. The accuracy of the five-pulse-per-second output is maintained only while the GPS 18-5Hz can compute a valid position fix. To obtain the most accurate results, the five-pulse-per-second output should be calibrated against a local time reference to compensate for cable and internal receiver delays and the local time bias.
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The default pulse width is 100 ms, however; it may be programmed in 20 ms increments between 20 ms and 180 ms as described in $PGRMC Section 4.1.2 Sensor Initialization Information (PGRMI), field <13>.
APPENDIX A: EARTH DATUM LIST
The following is a list of the Garmin GPS 18 Earth datum indices and the corresponding earth datum name (including the area of application): ADINDANEthiopia, Mali, Senegal, Sudan AFGOOYESomalia AIN EL ABD 1970Bahrain Island, Saudi Arabia ANNA 1 ASTRO 1965Cocos Island ARC 1950Botswana, Lesotho, Malawi, Swaziland, Zaire, Zambia, Zimbabwe ARC 1960Kenya, Tanzania ASCENSION ISLAND 1958Ascension Island ASTRO BEACON EIwo Jima Island AUSTRALIAN GEODETIC 1966Australia, Tasmania Island AUSTRALIAN GEODETIC 1984Australia, Tasmania Island ASTRO DOS 71/4St. Helena Island ASTRONOMIC STATION 1952Marcus Island ASTRO B4 SOROL ATOLLTern Island BELLEVUE (IGN)Efate and Erromango Islands BERMUDA 1957Bermuda Islands BOGOTA OBSERVATORYColombia CAMPO INCHAUSPEArgentina CANTON ASTRO 1966Phoenix Islands CAPE CANAVERALFlorida, Bahama Islands CAPESouth Africa CARTHAGETunisia CHATHAM 1971Chatham Island (New Zealand) CHUA ASTROParaguay CORREGO ALEGREBrazil DJAKARTA (BATAVIA)Sumatra Island (Indonesia) DOS 1968Gizo Island (New Georgia Islands) EASTER ISLAND 1967Easter Island EUROPEAN 1950Austria, Belgium, Denmark, Finland, France, Germany, Gibraltar, Greece, Italy, Luxembourg, Netherlands, Norway, Portugal, Spain, Sweden, Switzerland EUROPEAN 1979Austria, Finland, Netherlands, Norway, Spain, Sweden, Switzerland FINLAND HAYFORD 1910Finland GANDAJIKA BASERepublic of Maldives GEODETIC DATUM 1949New Zealand ORDNANCE SURVEY OF GREAT BRITAIN 1936England, Isle of Man, Scotland, Shetland Islands, Wales GUAM 1963Guam Island Rev. D Page 21

USB packets contain only the record ID, size, and data payload. Refer to the Garmin Device Interface Specification for details on how to form and parse Garmin USB packets. USB Packet: - 0x## - 0x## - data bytes (Record ID single byte) (Number of data bytes single byte) (See descriptions below)
The data bytes of each packet contain the record specified by the record ID. A description of each record follows.
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Satellite Data Record The satellite data has a record ID of 0x72 with 84 (0x54) data bytes. The data bytes contain the data for the 12 channels as described below. For each satellite, the following data is available: typedef struct { uint8 uint16 uint8 uint16 uint8 svid; snr; elev; azmth; status; //space vehicle identification (132 and 3364 for WAAS) //signal-to-noise ratio //satellite elevation in degrees //satellite azimuth in degrees //status bit-field
} cpo_sat_data; The status bit field represents a set of booleans described below: Bit Meaning when bit is one (1) 0 The unit has ephemeris data for the specified satellite. 1 The unit has a differential correction for the specified satellite. 2 The unit is using this satellite in the solution. This pattern is repeated for all 12 channels for a total of 12 X 7 bytes = 84 (0x54) bytes : typedef struct { cpo_sat_data cpo_sat_data cpo_sat_data cpo_sat_data cpo_sat_data cpo_sat_data cpo_sat_data cpo_sat_data cpo_sat_data cpo_sat_data cpo_sat_data cpo_sat_data } cpo_all_sat_data The RS-232 Packet for the Satellite Record looks like: - 0x10 - 0x72 - 0x54 - cpo_all_sat_data - 0x## - 0x10 - 0x03 (2s complement of the arithmetic sum of the bytes between the delimiters) (DLE) (ETX is last byte) (DLE is first byte) (Record ID single byte) (Number of data bytes single byte)
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The USB Packet for the Satellite Record looks like: - 0x72 (Record ID single byte) - 0x54 - cpo_all_sat_data Position Record The Position Record has a record identifier of typedef struct { float alt; float epe; float eph; float epv; int fix; double gps_tow; double lat; double lon; float lon_vel; float lat_vel; float alt_vel; float msl_hght; int leap_sec; long grmn_days; } cpo_pvt_data; alt epe eph epv fix Ellipsoid altitude (meters) Est pos error (meters) Pos err, horizontal (meters) Pos err, vertical (meters) 0 = no fix; 1 = no fix; 2 = 2D; 3 = 3D; 4 = 2D differential; 5 = 3D differential; 6 and greater = not defined gps_tow GPS time of week (sec) lat Latitude (radians) lon Longitude (radians) lon_vel Longitude velocity (meters/second) lat_vel Latitude velocity (meters/second) alt_vel Altitude velocity (meters/second) msl_hght Mean sea level height (meters) leap_sec UTC leap seconds grmn_days Garmin days (days since December 31, 1989) (Number of data bytes single byte)

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APPENDIX D: GPS 18 PC/ LVC/18-5Hz & WINDOWS SERIAL MOUSE ISSUE
Problem: It is possible for Windows to incorrectly interpret the NMEA 0183 output of the GPS 18 PC as the output of a Microsoft Serial BallPoint Mouse. When that happens, Windows loads drivers for the Serial BallPoint Mouse. This causes the cursor to move erratically about the display, clicking, right clicking, double clicking, dragging and dropping displayed items as it goes. On Windows 2000 and Windows XP, you may not experience the problem if you wait until after the computer is booted before connecting the GPS 18 PC to the serial communications port. This problem is not specific to the GPS 18 PC. Any NMEA 0183 device connected to a Windows computers serial port is likely to cause this problem. Below are several possible solutions to this problem. Note: If your GPS 18 PC came with Garmin nRoute Navigation Software, you will not have this problem; the unit is programmed to produce data according to the binary format that is described in Appendix B: Binary Phase Output Format. If you wish to use a different navigation software application with your GPS 18 PC, you will need to deselect the Phase Output Data option that is discussed in Solution 3 below. Solution 1: The easiest solution is to disable the Serial BallPoint mouse in the Device Manager. Of course, this solution assumes that you do not need to use a Serial BallPoint mouse with your computer. When the wild mouse problem occurs follow the steps below. 1. 2. 3. 4. Unplug the DB9 connector. Right-click the My Computer icon on your desktop and select Properties to open Device Manager. Go to the hardware tab of the resulting pop-up window and click on the Device Manager button. Right-click on Serial BallPoint Mouse and choose the option to Disable (NOT uninstall) this device.
Solution 2: Do not plug the DB9 connector into the computer until the computer is turned on and the operating system is completely booted up and running. Every time you use the GPS 18 PC/LVC, you will need to start the computer and operating system before making the connection between the GPS 18 PC and the computer. This solution usually works on Windows 2000 and Windows XP computers. Solution 3: Change the default output of the GPS 18 PC/LVC so that it does not automatically send NMEA 0183 data to the computer (change the default configuration to enable Phase Output Data). Use the Garmin Sensor Configuration Software, named SNSRCFG.EXE, provided on the Web site to enable Phase Output Data. SNSRCFG.EXE is included with the latest GPS 18 firmware, available at http://www.garmin.com/support/agree.jsp?product=010-00321-05. Please note that by enabling Phase Output Data, the device will no longer appear as a NMEA 0183 device to your computer. As a result, mapping applications that expect to hear NMEA 0183 data will not recognize your GPS 18 P/LVC until you re-enable the NMEA 0183 output, disabling the Phase Output Data in the process. Refer to Appendix E: Sensor Configuration Software for complete information about downloading the Sensor Configuration Software application. After the Sensor Configuration Software is installed and running on your computer, follow the steps below to change the default data output of the GPS 18 PC, LVC, or 18-5Hz. 1. Select the GPS 18 PC / LVC or the GPS 18-5Hz from the list of sensors and click OK. The Sensor Configuration Software opens with the default configuration file for the GPS 18, as shown on the next page. Select Config > Switch to NMEA Mode (or press the F10 key). Select Comm > Setup to open the Comm Setup Window.

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Select the Serial Port to which the GPS 18 is connected. Select Auto to have the program automatically determine the Baud Rate, or select Manual to manually select the Baud Rate of the GPS 18. Click OK when done.
Click the Connect icon , or select Comm > Connect to connect to the GPS 18. To view the current programming of the GPS 18, select Config > Get Configuration from GPS (or press the F8 key). The current programming of the GPS 18 is displayed in the window, as shown on the previous page. Open the Sensor Configuration Window by pressing the F6 key or selecting Config > Sensor Configuration. Place a check mark in the box next to Binary Output Data to change the GPS 18 to Garmin Mode. The unit will keep this change in the programming until you change it again in the software. Note: Selecting Config > Switch to Garmin Mode (or pressing the F11 key) only changes the unit to work in Garmin Mode until power is cycled through the unit again. For a more permanent change, refer to step 8 above.

Click OK.

10. When you are ready to upload the changes into the GPS 18, select Config > Send Configuration to GPS (or press the F9 key). The new configuration is then loaded into the GPS 18. 11. You may disconnect and close the software when finished. The software configuration can also be saved for future reference. Refer to Appendix E: Sensor Configuration Software for complete information about downloading the Sensor Configuration Software application.
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APPENDIX E: SENSOR CONFIGURATION SOFTWARE
SNSRCFG configures the GPS sensors based on user-selected parameters. Some application features include the ability to download GPS sensor configuration, maintain different configurations in files, and perform GPS sensor configurations quickly with the use of one function key. This section provides a brief overview of the Sensor Configuration Software. Refer to this section when using the software to configure your Garmin sensor.
Downloading the Sensor Configuration Software
The Garmin Sensor Configuration Software (SNSRCFG.exe) is available from the Garmin Web site. To download the software, start at http://www.garmin.com/oem, select the GPS 18, and then select Software Updates. The Garmin Sensor Configuration Software (SNSRCFG.exe) is included in the software update download.

Selecting a Model

After opening the program (snsrcfg.exe), the following screen appears. Select the radio button next to the type of Garmin sensor you are configuring.

Connecting to the Sensor

After selecting the type of sensor, the following window opens. This is the Main Interface Screen for the program. To configure your sensor, you must first connect to the sensor. 1. 2. 3. Select Config > Switch to NMEA Mode (or press the F10 key). Select Comm > Setup to open the Comm Setup Window. Select the Serial Port to which the sensor is connected. Select Auto to have the program automatically determine the Baud Rate, or select Manual to manually select the Baud Rate of the GPS 18. Click OK when done. Click the Connect icon , or select Comm > Connect. To view the current programming of the sensor, select Config > Get Configuration from GPS (or press the F8 key). The current programming of the sensor is displayed in the window shown to the right.

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File Menu

The File Menu allows you to open, save, and print sensor configurations. The items in the File Menu work like most Windows-based programs.

Comm Menu

The Comm (Communication) Menu allows you to set the port number, baud rate, and then connect and disconnect from the sensor. Setup: Opens the Comm Setup Window, shown to the left. Select the Serial Port to which the sensor is connected from the dropdown list. Then select Auto (the program determines the baud rate on its own) or Manual (you then enter the baud rate) for the Baud Rate entry. Connect: Select Connect to connect to the sensor to change or view the configuration. Disconnect: Select Disconnect to disconnect from the sensor.

Config Menu

The Config (Configuration) Menu allows you configure the sensor as it is connected. Sensor Configuration (F6): Opens the Sensor Configuration Window, shown to the right. Many of the fields in this window should be left alone. Please refer to the beginning of this manual for clarification about some of these fields. For the most part, this window is used to enter a new Latitude, Longitude, and Altitude for the sensor. This is especially helpful when you are programming the sensor for use in a particular geographic location. Resetting the Unit (Reset Unit) performs a reset on the unit, much like cycling the power. Resetting the non-volatile memory (Reset NonVol) will clear all of the data from the nonvolatile memory. NMEA Sentence Selections (F7): Displays the NMEA Sentence Selections Window. If the sentence is enabled, a check mark appears in the box to the left of the sentence name. Click the box to enable or disable to the sentence.
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Get Configuration From GPS (F8): Retrieves the current programming from the sensor. The programming is then displayed in the Main Interface Window. Send Configuration To GPS (F9): Sends the changes you have made to the programming to the sensor. Switch to NMEA Mode (F10): Switches the unit to NMEA Mode. The sensor must be in NMEA Mode when connected to this software. Switch to Garmin Mode (F11): Switches the unit to Garmin Mode. Update Software (F12): After you have downloaded a new software version for the sensor, you can update the sensor with the new software. Select Update Software and then select the file using the Open dialog box. You must locate both the *.rgn file and the updater.exe file.

View Menu

The View Menu allows you to view the NMEA sentences transmitted by the sensor. You can also customize how the program looks by showing and hiding the Toolbar and Status Bar.

Help Menu

The Help Menu displays the software version and copyright information.
For the latest free software updates (excluding map data) throughout the life of your Garmin products, visit the Garmin Web site at www.garmin.com.
Copyright 20042005 Garmin Ltd. or its subsidiaries Garmin International, Inc. 1200 East 151st Street, Olathe, Kansas 66062, U.S.A. Garmin (Europe) Ltd. Unit 5, The Quadrangle, Abbey Park Industrial Estate, Romsey, SO51 9DL, U.K. Garmin Corporation No. 68, Jangshu 2nd Road, Shijr, Taipei County, Taiwan www.garmin.com Part Number 190-00307-00 Rev. D