GPS 35 LP TracPak TM GPS SMART ANTENNA TECHNICAL SPECIFICATION Models: GPS35-LVC GPS35-LVS GPS35-HVS
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GARMIN 1200 E. 151st Street Olathe, Kansas 66062 (913) 397-8200 (913) 397-8282 FAX
2000 GARMIN Corporation, 1200 E. 151st Street, Olathe, KS 66062 All rights reserved. No part of this manual may be reproduced or transmitted in any 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. March, 2000 190-00148-00 Rev. E
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 35LP is a precision electronic NAVigation AID (NAVAID), any NAVAID can be misused or misinterpreted, and therefore become unsafe. Use the GPS 35LP at your own risk. To reduce the risk, carefully review and understand all aspects of this Technical Manual before using the GPS 35LP. When in actual use, carefully compare indications from the GPS 35LP to all available navigation sources including the information from other NAVAIDs, visual sightings, charts, etc. For safety, always resolve any discrepancies before continuing navigation. NOTE This device has been tested and found to comply with the limits for a Class B digital device, pursuant to Part 15 of the FCC Rules. Operation is subject to the following two 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 device 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 device does cause harmful interference to radio or television reception, which can be determined by turning the device off and on, you are 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 this device and the receiver. Connect this device to an outlet on a different circuit than that to which the receiver is connected. Consult the dealer or an experienced radio/TV technician for help. This device contains no user-serviceable parts. Repairs should only be performed by an authorized GARMIN service center. Unauthorized repairs or modifications to this device could void your warranty and your authority to operate this device under Part 15 regulations.

TABLE OF CONTENTS

Introduction 1.1 Overview 1.2 Features 1.3 Naming Conventions 1.4 Technical Specifications 1.5 Application Operational Characteristics 2.1 Self Test 2.2 Initialization 2.3 Navigation 2.4 Satellite Data Collection Hardware Interface 3.1 Mechanical Dimensions 3.2 Mounting Configurations and Options 3.3 Connection Wiring Description Software Interface 4.1 NMEA Received Sentences 4.2 NMEA Transmitted Sentences 4.3 Baud Rate Selection 4.4 One-Pulse-Per-Second Output 4.5 RTCM Received Data Earth Datums GPS 35LP Evaluation Kits Phase Data Output

A. B. C.

SECTION 1
INTRODUCTION 1.1 OVERVIEW The GARMIN GPS 35LP is a complete GPS receiver, including an embedded antenna, designed for a broad spectrum of OEM (Original Equipment Manufacturer) system applications. Based on the proven technology found in other GARMIN 12 channel GPS receivers, the GPS 35LP will track up to 12 satellites at a time while providing fast time-to-first-fix, one second navigation updates and low power consumption. Its far reaching capability meets the sensitivity requirements of land navigation as well as the dynamics requirements of high performance aircraft. The GPS 35LP design utilizes the latest technology and 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 35LP. This hardware capability combined with software intelligence makes the GPS 35LP easy to integrate and use. The GPS 35LP is designed to withstand rugged operating conditions and is completely water resistant. The GPS 35LP is a complete GPS receiver that requires minimal additional components be supplied by an OEM or system integrator. A minimum system must provide the GPS 35LP with a source of power and a clear view of the GPS satellites. The system may communicate with the GPS 35LP via a choice of two RS-232 compatible full duplex communication channels (-xVS series), or two full duplex CMOS channels (-xVC series). Internal memory backup allows the GPS 35LP to retain critical data such as satellite orbital parameters, last position, date and time. End user interfaces such as keyboards and displays are added by the application designer. 1.2 FEATURES

The GPS 35LP provides 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 3-10 meter position accuracy 5) Internal clock and memory are sustained by a rechargeable memory backup battery. The battery recharges during normal operation. 6) User initialization is not required 7) Navigation mode (2D or 3D) may be configured by the user 8) Two communication channels and user selectable baud rates allow maximum interface capability and flexibility 9) Highly accurate one-pulse-per-second output for precise timing measurements. Pulse width is configurable in 20 msec increments from 20 msec to 980 msec.
10) Binary Format Phase Data Output on TXD2 11) Flexible input voltage levels of 3.6Vdc to 6.0Vdc with overvoltage protection in the -LVx versions, and 6.0Vdc to 40Vdc in the -HVx versions. 12) FLASH based program memory. New software revisions upgradeable through serial interface.

1.3 Naming Conventions

The GPS 35LP Series TrackPack receivers are delineated with a three letter extension to designate the operating voltage range and the serial data voltage specification. High Voltage - GPS35-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 - GPS35-LVx designation indicates that the unit is designed to operated from a low voltage 3.6VDC to 6.0VDC supply. Operation at about 4VDC is the most power efficient mode of operation for the GPS35LP receiver. The unit is protected if a high voltage is inadvertently applied to the input. RS-232 Serial Data - GPS35-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 - GPS35-xVC designation means that the two bi-directional serial data ports use CMOS output buffers. The input buffers will accept either CMOS(TTL) voltage levels or RS232 voltage levels. This configuration is adequate for communicating directly with serial devices over short cable lengths (less than 20 meters). 1.4 TECHNICAL SPECIFICATIONS Specifications are subject to change without notice.
1.4.1 Physical Characteristics
1) Single construction integrated antenna/receiver. 2) Weight: 4.4 oz, (124.5 g), not including cable 3) Size: 2.230" (w) x 3.796" (l) x 1.047" (h), (56.64 mm x 96.42 mm x 26.60 mm)
1.4.2 Environmental Characteristics

1) Operating temperature: -30C to +85C (internal temperature) 2) Storage temperature: -40C to +90C 1.4.3 Electrical Characteristics 1) Input voltage: +3.6VDC to 6.0VDC regulated, 150mV 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) Power Down Input: 2.7V threshold

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) - 5.0 minutes AutoLocate TM (almanac known, initial position and time unknown) - 5 minutes search the sky (no data known) 4) Position accuracy: Differential GPS (DGPS): 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) Binary Format Phase Data 1.5 APPLICATION

Fig. 1, TYPICAL APPLICATION ARCHITECTURE

SECTION 2

OPERATIONAL CHARACTERISTICS This section describes the basic operational characteristics of the GPS 35LP. 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 35LP and periodically thereafter, the unit 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 memory test 3) Receiver test 4) Real-time clock test 5) Oscillator check In addition to the results of the above tests, the GPS 35LP will report software version information. 2.2 INITIALIZATION After the initial self test is complete, the GPS 35LP 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 35LP 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 5.0 minutes to achieve a navigation solution. The GPS 35LP 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 GPS 35LP following the occurrence of one or more of the following events: 1) Transportation over distances further than 1500 kilometers 2) Failure of the internal memory battery without system standby power 3) Stored date/time off by more than 30 minutes See Section 4 for more information on initializing the GPS 35LP.
2.3 NAVIGATION After the acquisition process is complete, the GPS 35LP 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 Normally the GPS 35LP will select the optimal navigation mode (2D or 3D) based on available satellites and geometry considerations. The host system, at its option, may command the GPS 35LP to choose a specific mode of navigation, such as 2D. The following modes are available: 1) 2D exclusively with altitude supplied by the host system (altitude hold mode) 2) 3D exclusively with altitude computed by the GPS 35LP 3) Automatic mode in which the board set determines the desired mode based on satellite availability and geometry considerations When navigating in the 2D mode (either exclusive or automatic), the GPS 35LP 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 more information on altitude control. The GPS 35LP will default to automatic differential mode looking for real-time differential corrections in RTCM SC-104 standard format, with message types 1,2,3, or 9, then attempt 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 GPS 35LP to choose differential only mode. When navigating in the differential only mode, the GPS 35LP will output a position only when a differential solution is available. 2.4 SATELLITE DATA COLLECTION The GPS 35LP will automatically update satellite orbital data as it operates. The intelligence of the GPS 35LP 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 receiver 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 receiver will search the sky as described above. Should the memory battery discharge, the unit needs to be powered on for several days to insure a sufficient recharge to maintain several months of clock operation and memory storage. System configuration information will not be lost due to battery discharge, only previous position, time and almanac data will be lost. 3) If the initial data is significantly inaccurate, the receiver perform an operation known as AutoLocate. This procedure is fully automatic and, under normal circumstances, will require 1.5

minutes to calculate a navigation solution. AutoLocate, unlike search the sky, does not require that the receiver continue to operate after a fix has been obtained.

SECTION 3

HARDWARE INTERFACE 3.1 MECHANICAL DIMENSIONS The GPS 35LP is a complete GPS receiver including antenna in a uniquely styled waterproof package.

3.1.1 GPS 35 Dimensions

(General tolerance 0.50mm)
Fig. 2 GPS 35LP Dimensions
3.2 MOUNTING CONFIGURATIONS AND OPTIONS The following mounting options are available for the GPS 35LP. Mounting is user configurable.

3.2.1 Magnetic Mount

The magnetic mount provides a firm, removable mounting attachment to any ferrous metal surface.
Fig. 3, Magnetic Mount Attachment

3.2.2 Trunk Lip Mount

The trunk lip mount provides a semi-permanent attachment to the trunk lip of most automobiles.
Fig. 4, Trunk Lip Mount Attachment

3.2.3 Suction Cup Mount

The suction cup bracket provides a removable mounting surface attached to the inside of a vehicle's windshield.
Fig. 5, Suction Cup Mount Attachment

3.2.4 Flange Mount

The flange mount allows for a permanent installation on a flat surface. This mounting configuration is ideal in applications in which the far side of the mounting surface is inaccessible.
Fig. 6, Flange Mount Attachment
3.3 CONNECTION WIRING DESCRIPTION The GPS 35LP features a stripped and pre-tinned cable assembly for connection flexibility. The following is a functional description of each wire in the cable assembly. Vin - Regulated +3.6V to +6V, 150 mA (maximum) in the -LVx versions. Typical operating current is 120 mA. Transients and overvoltages are protected by an internal 6.8V transient zener diode and a positive temperature coefficient thermistor. With voltages greater than 6.8Vdc the zener will draw several amps of current through the thermistor, causing it to heat rapidly and eventually power the unit off, unless an external fuse blows first. When proper supply voltages are returned, the thermistor will cool and allow the GPS 35-LVx to operate. The CMOS/TTL output buffers are powered by Vin, therefore a 3.6Vdc supply will create 3.6V logic output levels. In the -HVx versions, Vin can be an unregulated 6.0Vdc to 40Vdc, optimized for 12Vdc. Typical operating power is 800mW This voltage drives a switching regulator with a nominal 4.4Vdc output, which powers the internal linear regulators, and the CMOS output buffers. Black: GND - Power and Signal Ground White: 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. Blue: RXD1 - First Serial Asynchronous Input. RS-232 compatible with maximum input voltage range -25 < V < 25. This input may also be directly connected to standard 3 to 5Vdc CMOS logic. The minimum low signal voltage requirement is 0.8V, and the maximum high signal voltage requirement is 2.4V. Maximum load impedance is 4.7K ohms. This input may be used to receive serial initialization / configuration data, as specified in Section 4.1. Purple: TXD2 - Second Serial Asynchronous Output. Electrically identical to TXD1. This output provides phase data information for software version 2.03 or above. See Appendix C for details. Green: 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). Gray: 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 in the -LVx versions, and 0V and 4.4V in the -HVx. 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. Yellow: POWER DOWN - External Power Down Input. Inactive if not connected or less than 0.5V. Active if greater than 2.7V. Typical switch point is 2.0V @ 0.34 mA. Input impedance is 15K Ohms. Activation of this input powers the internal regulators off and drops the supply current below 20mA in the -LVx versions, and below 1mA in the -HVx. The computer will be reset when power is restored. Red:

Section 4

Software Interface
The GPS 35LP interface protocol design is based on the National Marine Electronics Associations NMEA 0183 ASCII interface specification, which is fully defined in NMEA 0183, Version 2.0 (copies may be obtained from NMEA, P.O. Box 50040, Mobile, AL, 36605, USA) and the Radio Technical Commission for Maritime Services RTCM Recommended Standards For Differential Navstar GPS Service, Version 2.1, RTCM Special Committee No. 104 (copies may be obtained from RTCM, P.O. Box 19087, Washington, DC, 20036, USA). The GPS 35LP interface protocol, in addition to transmitting navigation information as defined by NMEA 0183, transmits additional information using the convention of GARMIN proprietary sentences. The following sections describe the data format of each sentence transmitted and received by the GPS 35LP sensor. The baud rate selection, one-pulse-per-second output interfaces and RTCM differential GPS input are also described.

NMEA Received sentences

The subsequent paragraphs define the sentences which can be received on RXD1 by the GPS 35LP receivers. Null fields in the configuration sentence indicate no change in the particular configuration parameter. All sentences received by the GPS 35LP must be terminated with <CR><LF>, but do not require the checksum *hh. The checksum is used for parity checking data and it is recommended that the checksum be used in environments containing high electromagnetic noise. It is generally not required in normal PC environments. Sentences may be truncated by <CR><LF> after any data field and valid fields up to that point will be acted on by the GPS 35LP. 4.1.1 Almanac Information (ALM)
$GPALM,<1>,<2>,<3>,<4>,<5>,<6>,<7>,<8>,<9>,<10>,<11>,<12>,<13>,<14>,<15> *hh<CR><LF> The $GPALM sentence can be used to initialize the receivers stored almanac information if battery backup has failed. <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 sensor board during almanac download. This field can be null or any number when sending almanac to the sensor board. Number of current ALM sentence. This field can be null or any number when sending almanac to the sensor board. Satellite PRN number, 01 to 32. GPS week number. SV health, bits 17-24 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 afo clock parameter af1 clock parameter

<4> <5> <6> <7> <8> <9> <10> <11> <12> <13> <14>
All configuration changes take effect after receipt of a valid value except baud rate and PPS mode. Baud rate and PPS mode changes take effect on the next power cycle or an external reset event. 4.1.4 Additional Sensor Configuration Information (PGRMC1)
The $PGRMC1 sentence provides additional information used to configure the sensor board operation. Configuration parameters are stored in non-volatile memory and retained between power cycles. The GPS 35LP 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 board. $PGRMC1,<1>,<2>,<3>,<4>,<5>,<6>,<7>*hh<CR><LF> <1> <2> <3> <4> <5> <6> <7> NMEA output time 1-900 (sec). Binary Phase Output Data, 1 = Off, 2 = On. Position pinning, 1 = Off, 2 = On. DGPS beacon frequency 0.0, 283.5 325.0 kHz in 0.5 kHz steps. DGPS beacon bit rate 0, 25, 50, 100, or 200 bps. DGPS beacon auto tune on station loss, 1 = Off, 2 = On. Activate NMEA 2.30 mode indicator, 1 = Off, 2 = On.
Configuration changes take effect on the next power cycle or an external reset event. At power up or external reset, a stored beacon frequency other than 0.0 causes the GPS 35LP to tune the beacon receiver. 4.1.5 Output Sentence Enable/Disable (PGRMO)
The $PGRMO sentence provides the ability to enable and disable specific output sentences. The following sentences are enabled at the factory: GPGGA, GPGSA, GPGSV, GPRMC, and PGRMT. $PGRMO,<1>,<2>*hh<CR><LF> <1> <2> Target sentence description (e.g., PGRMT, GPGSV, etc.) Target sentence mode, where: 0 = disable specified sentence 1 = enable specified sentence 2 = disable all output sentences 3 = enable all output sentences (except GPALM)
The following notes apply to the PGRMO input sentence: 1) If the target sentence mode is 2 (disable all) or 3 (enable all), the target sentence description is not checked for validity. In this case, an empty field is allowed (e.g., $PGRMO,,3), or the mode field may contain from 1 to 5 characters. 2) If the target sentence mode is 0 (disable) or 1 (enable), the target sentence description field must be an identifier for one of the sentences being output by the GPS 25LP. 3) If either the target sentence mode field or the target sentence description field is not valid, the PGRMO sentence will have no effect.

4) $PGRMO,GPALM,1 will cause the sensor board to transmit all stored almanac information. All other NMEA sentence transmission will be temporarily suspended. 4.1.6 Tune DGPS Beacon Receiver (PSLIB)
The $PSLIB sentence provides the ability to tune a GARMIN GBR-21 or equivalent beacon receiver. $PSLIB,<1>,<2>*hh<CR><LF> <1> <2> Beacon tune frequency, 0.0, 283.5 325.0 kHz in 0.5 kHz steps Beacon bit rate, 0, 25, 50, 100, or 200 bps
If valid data is received, the GPS 35LP will store it in the EEPROM and echo the PSLIB command to the beacon receiver. At power up or external reset, any stored frequency other than 0.0 causes the GPS 35LP to tune the beacon receiver.
NMEA Transmitted Sentences
The subsequent paragraphs define the sentences which can be transmitted on TXD1 by the GPS 35LP receivers. 4.2.1 Sentence Transmission Rate
Sentences are transmitted with respect to the user selected baud rate. Regardless of the selected baud rate, the information transmitted by the GPS 35LP is referenced to the one-pulse-per-second output pulse immediately preceding the GPRMC sentence. The GPS 35LP will transmit each sentence (except where noted in particular transmitted sentence descriptions) at a periodic rate based on the user selected baud rate and user selected output sentences. The sensor board will transmit the selected sentences contiguously. The contiguous transmission starts at a GPS second boundary. The length of the transmission can be determined by the following equation and tables: total characters to be transmitted length = -------------------------------------------characters transmitted per sec Baud 19200 Sentence GPGGA GPGSA GPGSV GPRMC GPVTG PGRMB PGRME PGRMT PGRMV PGRMF LCGLL LCVTG characters_transmitted_per_sec 1920 max_characters 44 39
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>. The factory set defaults will result in a once per second transmission at the NMEA specification transmission rate of 4800 baud.

4.2.2 Transmitted Time The GPS 35LP receivers output UTC (Coordinated Universal Time) date and time of day in the transmitted sentences. Prior to the initial position fix, the date and time of day are provided by the onboard clock. After the initial position fix, the date and time of day are calculated using GPS satellite information and are synchronized with the one-pulse-per-second output. The GPS 35LP 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, DC, 20402, USA). When a positive leap second is required, the second is inserted beginning at 23h 59m 60s of the last day of a month and ending at 0h 0m 0s of the first day of the following month. The minute containing the leap second is 61 seconds long. The GPS 35LP would have transmitted this information for the leap second added December 31, 1989 as follows: Date 010190 Time 000000
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 35LP will not transmit the time of day 23h 59m 59s for the day from which the leap second is removed. 4.2.3 Global Positioning System Almanac Data (ALM)
<field information> can be found in section 4.1.1. $GPALM,<1>,<2>,<3>,<4>,<5>,<6>,<7>,<8>,<9>,<10>,<11>,<12>,<13>,<14>,<15>*hh<CR><LF> Almanac sentences are not normally transmitted. Almanac transmission can be initiated by sending the sensor board a $PGRMO,GPALM,1 command. Upon receipt of this command the sensor board will transmit available almanac information on GPALM sentences. During the transmission of almanac sentences other NMEA data output will be temporarily suspended. <field information> can be found in section 4.1.1. 4.2.4 Global Positioning System Fix Data (GGA)

Baud Rate Selection

Baud rate selection can be performed by sending the appropriate configuration sentence to the sensor board as described in the NMEA input sentences selection. (Section 4.1)
One-Pulse-Per-Second Output
The highly accurate one-pulse-per-second output is provided for applications requiring precise timing measurements. The signal is generated after the initial position fix has been calculated and continues until power down. The rising edge of the signal is synchronized to the start of each GPS second. Regardless of the selected baud rate, the information transmitted by the GPS 35LP receiver is referenced to the pulse immediately preceding the NMEA 0183 RMC sentence. The accuracy of the one-pulse-per-second output is maintained only while the GPS 35LP can compute a valid position fix. To obtain the most accurate results, the one-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. The default pulse width is 100 msec, however; it may be programmed is 20 msec increments between 20 msec and 980 msec as described in $PGRMC Section 4.1.3 character <13>.

RTCM Received Data

Position accuracy of less than 5 meters can be achieved with the GPS 35LP by using Differential GPS (DGPS) real-time pseudo-range correction data in RTCM SC-104 format, with message types 1, 2, 3, and 9. These corrections can be received by the GPS 35LP receiver on RXD2. Correction data at speeds of 300, 600, 1200, 2400, 4800 or 9600 baud can be utilized, as the GPS 35LP automatically detects the incoming baud rate. For details on the SC-104 format, refer to RTCM Paper 134-89/SC 10468 by the Radio Technical Commission for Maritime Services.

Appendix A

Earth Datums
The following is a list of the GARMIN GPS 35LP earth datum indexes and the corresponding earth datum name (including the area of application): ADINDAN - Ethiopia, Mali, Senegal, Sudan AFGOOYE - Somalia AIN EL ABD 1970 - Bahrain Island, Saudi Arabia ANNA 1 ASTRO 1965 - Cocos Island ARC 1950 - Botswana, Lesotho, Malawi, Swaziland, Zaire, Zambia, Zimbabwe ARC 1960 - Kenya, Tanzania ASCENSION ISLAND 1958 - Ascension Island ASTRO BEACON E - Iwo Jima Island AUSTRALIAN GEODETIC 1966 - Australia, Tasmania Island AUSTRALIAN GEODETIC 1984 - Australia, Tasmania Island ASTRO DOS 71/4 - St. Helena Island ASTRONOMIC STATION 1952 - Marcus Island ASTRO B4 SOROL ATOLL - Tern Island BELLEVUE (IGN) - Efate and Erromango Islands BERMUDA 1957 - Bermuda Islands BOGOTA OBSERVATORY - Colombia CAMPO INCHAUSPE - Argentina CANTON ASTRO 1966 - Phoenix Islands CAPE CANAVERAL - Florida, Bahama Islands CAPE - South Africa CARTHAGE - Tunisia CHATHAM 1971 - Chatham Island (New Zealand) CHUA ASTRO - Paraguay CORREGO ALEGRE - Brazil DJAKARTA (BATAVIA) - Sumatra Island (Indonesia) DOS 1968 - Gizo Island (New Georgia Islands) EASTER ISLAND 1967 - Easter Island EUROPEAN 1950 - Austria, Belgium, Denmark, Finland, France, Germany, Gibraltar, Greece, Italy, Luxembourg, Netherlands, Norway, Portugal, Spain, Sweden, Switzerland EUROPEAN 1979 - Austria, Finland, Netherlands, Norway, Spain, Sweden, Switzerland FINLAND HAYFORD 1910 - Finland GANDAJIKA BASE - Republic of Maldives GEODETIC DATUM 1949 - New Zealand ORDNANCE SURVEY OF GREAT BRITAIN 1936 - England, Isle of Man, Scotland, Shetland Islands, Wales GUAM 1963 - Guam Island GUX 1 ASTRO - Guadalcanal Island HJORSEY 1955 - Iceland HONG KONG 1963 - Hong Kong INDIAN - Bangladesh, India, Nepal INDIAN - Thailand, Vietnam IRELAND 1965 - Ireland ISTS O73 ASTRO 1969 - Diego Garcia JOHNSTON ISLAND 1961 - Johnston Island

lat lon lon_vel lat_vel alt_vel
Latitude (rad) Longitude (rad) Longitude velocity (mt/sec) Latitude velocity (mt/sec) Altitude velocity (mt/sec)
Receiver Measurement Record - 0x10 - 0x29 - 0xE2 - cpo_rcv_type - one byte chksum - 0x10 - 0x03 typedef struct { unsigned long double unsigned int char unsigned char char char } cpo_rcv_sv_type; typedef struct { double int cpo_rcv_sv_type } cpo_rcv_type; rcvr_tow rcvr_wn cycles pr phase slp_dtct snr_dbhz svid valid (dle is first byte) (receiver record identifier) (size of data) (see below) (the addition of bytes between the delimiters should equal 0) (dle) (etx)
cycles; pr; phase; slp_dtct; snr_dbhz; svid; valid;
rcvr_tow; rcvr_wn; sv[12];
Receiver time of week (sec) Receiver week number Number of accumulated cycles pseudo range (mt) to convert to (0 -359.999) multiply by 360.0 and divide by 2048.= no cycle slip detected; non 0 = cycle slip detected Signal strength Satellite number (0 - 31) Note - add 1 to offset to current svid numbers 0 = information not valid; non 0 = information valid
dle and etx bytes: Software written to receive the two records should filter dle and etx bytes as described below: typedef enum { dat, dle, etx } rx_state_type; char int rx_state_type
in_que[256]; in_que_ptr = 0; 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; } }
GARMIN Phase Monitor Program - gps25pm.exe
Command Line Arguments default: /com1 /b:9600 Description: GPS25PM.EXE is designed to interface with a Garmin GPS 25 XL or GPS 25LP sensor boards and the GPS 35LP sensors. The program will perform the following functions: - display and log phase data output by GPS sensors. - upload almanac, position, and time information. - download almanac and ephemeris information. GPS25PM.EXE is a DOS based program and will run on IBM 80286 or greater compatible PCs. Displayed Information: The GPS25PM.EXE display page is divided into 3 sections. The top-most section contains the following information updated at once a second: A. Position 1. WGS 84 Latitude, Longitude (degrees - minutes) - 0.0001 minute resolution. 2. Ellipsoid Altitude (meters) - 1 meter resolution. B. Velocity 1. Each of 3 axis (meters per second) - 0.01 m/s resolution. 2. Altitude (meters/minute) - 1 mt/m resolution. 3. Ground Speed (kilometers/hour) - 0.1 km/h resolution C. Estimated Position Error - Vertical, Horizontal, Total (meters) - 1 meter resolution D. Track - (0 - 359 degrees) - 0.1 degree resolution E. Time 1. GPS time (hours - minutes - seconds) - 1 sec. resolution (not leap second corrected) 2. Receiver Time of Week (GPS seconds) - 0.00000001 sec. resolution. The middle section contains receiver measurement information for satellites which the GPS sensor is currently tracking. This information is updated once at second: A Satellite Number (1 - 32) B. Signal to Noise Ratio (dbHz) - 1 dbHz resolution. C. Phase (0 - 359 degrees) - 0.1 degree resolution. D. Pseudo Range (meters) - 1 meter resolution. E. Accumulated Cycles (cycles) - 1 cycle resolution.

211.7 -0.19 -0.31 0.16 23
212.6 -0.19 -0.30 0.16 23
213.5 -0.19 -0.30 0.16 23
214.4 -0.19 -0.30 0.16 23
215.4 -0.19 -0.30 0.16 23
GARMIN Corporation 1200 East 151st Street Olathe, KS 66062 (913)397-8200 (913)397-8282 FAX

190-00148-00 Rev. E