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

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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
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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>
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Additional Sensor Configuration Information (PGRMC1)
The $PGRMC1 sentence provides additional information used to configure the GPS sensor 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 PGRMC1 sentence will contain the current default values. Current default values can also be obtained by sending $PGRMC1E to the GPS sensor. $PGRMC1,<1>,<2>,<3>,<4>,<5>,<6>,<7>,<8>,<9>,<10>,<11>,<12>,<13>*hh<CR><LF> NMEA 0183 output time 1 to 900 (sec). Not applicable to GPS 18-5Hz, which always outputs data at 5 Hz (200 ms) <2> Binary Phase Output Data, 1 = Off, 2 = On. <3> Automatic Position Averaging when Stopped, 1 = Off, 2 = On <4> No Effect (DGPS beacon frequency: 0.0, 283.5 to 325.0 kHz in 0.5 kHz steps) <5> No Effect (DGPS beacon bit rate: 0, 25, 50, 100, or 200 bps) <6> No Effect (DGPS beacon scanning, 1 = Off, 2 = On) <7> NMEA 0183 version 2.30 mode indicator, 1 = Off, 2 = On <8> DGPS WAAS mode, W = WAAS Enabled, N = WAAS Disabled <9> Power Save Mode, P = Power Save mode, N = Normal <10> Adaptive Transmission Enabled, 1 = Off, 2 = On <11> Auto Power Off, 1 = Off, 2 = On <12> Power On with External Charger, 1 = Off, 2 = On <13> Measurement Pulse Output Auto Off Mode, 1 = Off, 2 = On Configuration changes take effect immediately, with the exception of Binary Phase Output Data, which takes effect on the next power cycle or a reset event. Send the sentence $PGRMI,,,,,,,R to command a reset (refer to Section 4.1.2 Sensor Initialization Information (PGRMI)). If the GPS sensor is in the Binary data mode, it is necessary to send the following eight-byte data stream to temporarily change the data format to NMEA 0183. Then follow by sending a PGRMC1 sentence that turns off the Binary Phase Output Data format: 10 0A 00 CE (Hexadecimal) <1>

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Global Positioning System Fix Data (GGA)
<1> <2> <3> <4> <5> <6> <7> <8> <9> <10> <11> <12> UTC time of position fix, hhmmss format for GPS 18 PC or LVC; hhmmss.s format for GPS 185Hz Latitude, ddmm.mmmm format for GPS 18 PC/LVC; ddmm.mmmmm for GPS 18-5Hz (leading zeros will be transmitted) Latitude hemisphere, N or S Longitude, dddmm.mmmm format for GPS 18 PC/LVC; dddmm.mmmmm for GPS 18-5Hz (leading zeros will be transmitted) Longitude hemisphere, E or W GPS quality indication, 0 = fix not available, 1 = Non-differential GPS fix available, 2 = Differential GPS (WAAS) fix available, 6 = Estimated Number of satellites in use, 00 to 12 (leading zeros will be transmitted) Horizontal dilution of precision, 0.5 to 99.9 Antenna height above/below mean sea level, -9999.9 to 99999.9 meters Geoidal height, -999.9 to 9999.9 meters Null (Differential GPS Null (Differential Reference Station ID)
$GPGGA,<1>,<2>,<3>,<4>,<5>,<6>,<7>,<8>,<9>,M,<10>,M,<11>,<12>*hh<CR><LF>
GPS DOP and Active Satellites (GSA)
<1> <2> <3> <4> <5> <6> Mode, M = manual, A = automatic Fix type, 1 = not available, 2 = 2D, 3 = 3D PRN number, 01 to 32, of satellite used in solution, up to 12 transmitted (leading zeros will be transmitted) Position dilution of precision, 0.5 to 99.9 Horizontal dilution of precision, 0.5 to 99.9 Vertical dilution of precision, 0.5 to 99.9
$GPGSA,<1>,<2>,<3>,<3>,<3>,<3>,<3>,<3>,<3>,<3>,<3>,<3>,<3>,<3>,<4>,<5>,<6>*hh<CR><LF>
GPS Satellites in View (GSV)
<1> <2> <3> <4> <5> <6> <7>
$GPGSV,<1>,<2>,<3>,<4>,<5>,<6>,<7>,.<4>,<5>,<6>,<7>*hh<CR><LF> Total number of GSV sentences to be transmitted Number of current GSV sentence Total number of satellites in view, 00 to 12 (leading zeros will be transmitted) Satellite PRN number, 01 to 32 (leading zeros will be transmitted) Satellite elevation, 00 to 90 degrees (leading zeros will be transmitted) Satellite azimuth, 000 to 359 degrees, true (leading zeros will be transmitted) Signal to noise ratio (C/No) 00 to 99 dB, null when not tracking (leading zeros will be transmitted) NOTE: Items <4>,<5>,<6>, and <7> repeat for each satellite in view to a maximum of four (4) satellites per sentence. Additional satellites in view information must be sent in subsequent bursts of NMEA 0183 data. These fields will be null if unused.

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Recommended Minimum Specific GPS/TRANSIT Data (RMC)
<1> <2> <3> <4> <5> <6> <7> <8> <9> <10> <11> <12> UTC time of position fix, hhmmss format for GPS 18 PC/LVC; hhmmss.s format for GPS 18-5Hz Status, A = Valid position, V = NAV receiver warning Latitude, ddmm.mmm format for GPS 18 PC/LVC; ddmm.mmmmm format for GPS 18-5Hz (leading zeros must be transmitted) Latitude hemisphere, N or S Longitude, ddmm.mmm format for GPS 18 PC/LVC; ddmm.mmmmm format for GPS 18-5Hz (leading zeros must be transmitted) Longitude hemisphere, E or W Speed over ground, GPS 18 PC and LVC: 000.0 to 999.9 knots, GPS 18-5Hz: 000.00 to 999.99 knots (leading zeros will be transmitted) Course over ground, 000.0 to 359.9 degrees, true (leading zeros will be transmitted) UTC date of position fix, ddmmyy format Magnetic variation, 000.0 to 180.0 degrees (leading zeros will be transmitted) Magnetic variation direction, E or W (westerly variation adds to true course) Mode indicator (only output if NMEA 0183 version 2.30 active), A = Autonomous, D = Differential, E = Estimated, N = Data not valid
$GPRMC,<1>,<2>,<3>,<4>,<5>,<6>,<7>,<8>,<9>,<10>,<11>,<12>*hh<CR><LF>
Track Made Good and Ground Speed (VTG)
<1> <2> <3> <4> <5> True course over ground, GPS 18 PC and LVC: 000 to 359 degrees, GPS 18-5Hz: 000.0 to 359.0 degrees(leading zeros will be transmitted) Magnetic course over ground, 000 to 359 degrees, GPS 18-5Hz: 000.0 to 359.0 degrees(leading zeros will be transmitted) Speed over ground, GPS 18 PC and LVC: 000.0 to 999.9 knots, GPS 18-5Hz: 000.00 to 999.99 knots (leading zeros will be transmitted) Speed over ground, GPS 18 PC and LVC: 0000.0 to 1851.8 kilometers per hour, GPS 18-5Hz: 0000.00 to 1851.89 (leading zeros will be transmitted) Mode indicator (only output if NMEA 0183 version 2.30 active), A = Autonomous, D = Differential, E = Estimated, N = Data not valid
$GPVTG,<1>,T,<2>,M,<3>,N,<4>,K,<5>*hh<CR><LF>
Geographic Position (GLL)
<1> <2> <3> <4> <5> <6> <7> Latitude, ddmm.mmm format for GPS 18 PC/LVC; ddmm.mmmmm format for GPS 18-5Hz (leading zeros must be transmitted) Latitude hemisphere, N or S Longitude, ddmm.mmm format for GPS 18 PC/LVC; ddmm.mmmmm format for GPS 18-5Hz (leading zeros must be transmitted) Longitude hemisphere, E or W UTC time of position fix, hhmmss format for GPS 18 PC/LVC; hhmmss.s format for GPS 185Hz Status, A = Valid position, V = NAV receiver warning Mode indicator (only output if NMEA 0183 version 2.30 active), A = Autonomous, D = Differential (WAAS), E = Estimated, N = Data not valid
$GPGLL,<1>,<2>,<3>,<4>,<5>,<6>,<7>*hh<CR><LF>

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4.2.10 Estimated Error Information (PGRME)
$PGRME,<1>,M,<2>,M,<3>,M*hh<CR><LF> <1> <2> <3> Estimated horizontal position error (HPE), 0.0 to 999.9 meters Estimated vertical position error (VPE), 0.0 to 999.9 meters Estimated position error (EPE), 0.0 to 999.9 meters
4.2.11 GPS Fix Data Sentence (PGRMF)
$PGRMF,<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> GPS week number (0 to 1023) GPS seconds (0 to 604799) UTC date of position fix, ddmmyy format UTC time of position fix, hhmmss format for GPS 18 PC/LVC; hhmmss.s format for GPS 185Hz GPS leap second count Latitude, ddmm.mmm format for GPS 18 PC/LVC; ddmm.mmmmm format for GPS 18-5Hz (leading zeros must be transmitted) Latitude hemisphere, N or S Longitude, ddmm.mmm format for GPS 18 PC/LVC; ddmm.mmmmm format for GPS 18-5Hz (leading zeros must be transmitted) Longitude hemisphere, E or W Mode, M = manual, A = automatic Fix type, 0 = no fix, 1 = 2D fix, 2 = 3D fix Speed over ground, 0 to 1851 kilometers/hour Course over ground, 0 to 359 degrees, true Position dilution of precision, 0 to 9 (rounded to nearest integer value) Time dilution of precision, 0 to 9 (rounded to nearest integer value)
4.2.12 Sensor Status Information (PGRMT)
The Garmin Proprietary sentence $PGRMT gives information concerning the status of the GPS sensor. This sentence is transmitted once per minute regardless of the selected baud rate. $PGRMT,<1>,<2>,<3>,<4>,<5>,<6>,<7>,<8>,<9>*hh<CR><LF> <1> <2> <3> <4> <5> <6> <7> <8> <9> Product, model and software version (variable length field, for example, GPS 18 VER 2.05) ROM checksum test, P = pass, F = fail Receiver failure discrete, P = pass, F = fail Stored data lost, R = retained, L = lost Real time clock lost, R = retained, L = lost Oscillator drift discrete, P = pass, F = excessive drift detected Data collection discrete, C = collecting, null if not collecting GPS sensor temperature in degrees C GPS sensor configuration data, R = retained, L = lost

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

cycles; pr; phase; slp_dtct; snr_dbhz; svid; valid;
rcvr_tow; rcvr_wn; sv[ 12 ];
Receiver time of week (seconds) Receiver week number Number of accumulated cycles Pseudorange (meters) To convert to (0 to 359.999) multiply by 360.0 and divide by 2048.= no cycle slip detected; non-zero = cycle slip detected Signal strength - db Hz Satellite number (0 to 31; 119 to 138 for WAAS). Note: add 1 to offset to current svid 0 = information not valid; non-zero = information valid
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DLE and ETX bytes: Sample C code to receive the two records should filter DLE and ETX bytes as described below: typedef enum { DAT, DLE, ETX } rx_state_type; /* Declare and initialize static variables */ static char in_que[ 256 ]; static int in_que_ptr = 0; static rx_state_type rx_state = DAT;. void add_to_que( char data ) { #define DLE_BYTE 0x10 #define ETX_BYTE 0x03 if ( rx_state == DAT ) { if ( data == DLE_BYTE ) { rx_state = DLE; } else { in_que[ in_que_ptr++ ] = data; } } else if ( rx_state == DLE ) { if ( data == ETX_BYTE ) { rx_state = ETX; } else { rx_state = DAT; in_que[ in_que_ptr++ ] = data; } } else if ( rx_state == ETX ) { if ( data == DLE_BYTE ) { rx_state = DLE; } } if ( in_que_ptr > 255 ) { in_que_ptr = 0; } }
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APPENDIX C: CHANGING THE BAUD RATE IN GARMIN MODE
In certain cases, you may need to change the default baud rate of your Garmin GPS receiver while in Garmin mode. Follow these steps to temporarily change the baud rate. Refer to the Garmin Device Interface Specification for details on how to form and parse Garmin packets. At the time of this printing, these specs are available from the technical suppport section of our Web site: http://www.garmin.com/support/commProtocol.html. 1. Turn off all requests by transmitting packet: id = IOP_RQST_DATA (0x1C) data = 0 (16-bit unsigned integer ) 2. 3. The GPS unit will respond by sending a packet with id = IOP_ACK_BYTE (0x06) After you receive the above packet, transmit packet: id = IOP_BAUD_RQST_DATA (0x30) data = baud rate to change to (32-bit unsigned integer; for example, 38400) 4. The GPS unit will respond by sending a packet: id = IOP_BAUD_ACPT_DATA (0x31) data = highest acceptable baud rate closest to what was requested (32-bit unsigned integer; for example, 38361 decimal) 5. Determine the actual baud rate value from the data sent in step 4. This value will be within +/- 5% of the actual baud rate. (For example, the GPS unit might send a baud rate of 38361, which correlates to a baud rate of 38400). If the baud rate in step 5 is acceptable, transmit packet: id = IOP_ACK_BYTE (0x06) data = IOP_BAUD_ACPT_DATA (0x31) 7. 8. 9. Sleep for a small amount of time, about 100 milliseconds, to make sure the packet in (6) was successfully transmitted to the GPS unit. Close the current connection to the GPS unit and immediately open a new connection with the new baud rate obtained in step 5. Immediately after establishing a connection, transmit packet: id = IOP_CMND_DATA (0x0A) data = IOP_ACK_PING (0x3A) 10. The GPS will respond by sending a packet: id = IOP_ACK_BYTE (0x06) data = IOP_CMND_DATA (0x0A) 11. After you receive the above packet, transmit the same packet in step 9 again. id = IOP_CMND_DATA (0x0A) data = IOP_ACK_PING (0x3A) 12. The GPS will respond again with the same packet in step 10. id = IOP_ACK_BYTE (0x06) data = IOP_CMND_DATA (0x0A) 13. The baud rate has been successfully changed upon receiving the above packet. If the GPS unit does not receive these two IOP_CMND_DATA packets within two seconds, it will reset its baud rate to 9600.

GPS 18 Technical Specifications (190-00307-00) Page 29
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.
GPS 18 Technical Specifications (190-00307-00) Page 31
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.

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