Interface Specifications - Standard ICs

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©2006 Leadtek Research Inc. All rights reserved. No part of this publication may be reproduced, stored in a retrieval 

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Leadtek reserves the right to make changes in the product design without reservation and without notification to its 

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Customer Support 

• Visit our Web site at www.leadtek.com.tw. 

• For support via e-mail, submit your question at service@leadtek.com.tw. 

Leadtek Research Inc. 18F, 166, Chien-Yi Rd., Chung Ho, Taipei Hsien, Taiwan (235) 

Telephone: +886-(0)2 8226 5800 

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gpssales@leadtek.com.tw 

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Leadtek Research USA 

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gps@leadtek.com 

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Telephone: +31 (0)20 4 109 100 

Fax: +31 (0)20 4 109 111 

gps_sales@leadtek.nl 

gps@leadtek.nl

Revision History: 

Revision Release Date Issuer Change Description 

1.3 2006/03/13 J. Lu Update new reel tapping package drawing and ordering info. 

1.4 2006/03/21 J. Lu Update Block Diagram and U.S. contact info. Corrected 

mechanical drawing and PCB layout drawing. 

i

Contents 

INTRODUCTION..........................................................................................................................1 

FEATURES .....................................................................................................................................1 

Hardware and Software ...........................................................................................................1 

Performance.............................................................................................................................1 

Interface ...................................................................................................................................1 

ADVANTAGES................................................................................................................................1 

RECOMMENDED DESIGN................................................................................................................2 

SPECIFICATIONS........................................................................................................................3 

TECHNICAL SPECIFICATIONS .........................................................................................................3 

ENVIRONMENTAL CHARACTERISTICS............................................................................................4 

PHYSICAL CHARACTERISTICS........................................................................................................4 

INTERFACE SPECIFICATIONS..........................................................................................................4 

SOFTWARE ...................................................................................................................................5 

SIRF GSW3 ..................................................................................................................................5 

Options .....................................................................................................................................5 

TTFF PERFORMANCE....................................................................................................................6 

Test Setup .................................................................................................................................6 

Leadtek LR9805-III TTFF Test Results....................................................................................7 

ELECTRICAL SPECIFICATIONS.............................................................................................9 

BLOCK DIAGRAM ..........................................................................................................................9 

ABSOLUTE MAXIMUM RATINGS....................................................................................................9 

OPERATING CONDITIONS...............................................................................................................9 

BACKUP BATTERY CONDITIONS....................................................................................................9 

DC CHARACTERISTICS ................................................................................................................10 

INTERFACE SPECIFICATION................................................................................................11 

PHOTOS AND PIN POSITIONS........................................................................................................11 

PIN SETTINGS ..............................................................................................................................11 

PIN FUNCTIONS ...........................................................................................................................12 

Pin Name................................................................................................................................12 

Description.............................................................................................................................12 

BACKUP BATTERY DESIGN..........................................................................................................13 

Reference Design....................................................................................................................13 

MECHANICAL DIMENSIONS.................................................................................................14 

OUTLINE DRAWING.....................................................................................................................14 

RECOMMENDED PCB LAYOUT....................................................................................................15 

STRIP LINE LAYOUT....................................................................................................................16 

REFLOW PROFILE ........................................................................................................................16 

AUTOMATED MANUFACTURING COMPONENTS ...........................................................................17 

Reel Taping Specification ......................................................................................................17 

Polystyrene Alloy Taping Specifications................................................................................18 

Ordering Information.............................................................................................................18 

ii

APPENDIX A ...............................................................................................................................19 

SOFTWARE OPTIONS....................................................................................................................19 

Trickle Power Mode...............................................................................................................19 

Push-to-Fix Mode...................................................................................................................19 

Average Current for GPSCLK Trickle Power, 200msec On Time.........................................20 

Item.........................................................................................................................................20 

Dead Reckoning .....................................................................................................................20 

SiRFLoc A-GPS Client Software............................................................................................21 

GMonitor Software.................................................................................................................21 

GLOSSARY..................................................................................................................................22 

iii

LR9805-III GPS Module 

Introduction 

The Leadtek LR9805-III GPS module is a high sensitivity, low power, Surface Mount Device (SMD). 

This 20-channel global positioning system (GPS) receiver is designed for a broad spectrum of OEM 

applications and is based on the fast and deep GPS signal search capabilities of SiRFstarIII 

architecture. Leadtek LR9805-III is designed to allow quick and easy integration into 

GPS-related applications such as: 

• PDA, Pocket PC, and other computing devices 

• Car and Marine Navigation 

• Fleet Management /Asset Tracking 

• Automatic Vehicle Location (AVL) and Location-Based Services 

• Hand-Held Device for Personal Positioning and Navigation 

Features 

Hardware and Software 

• Based on the high performance features of the SiRFstarIII chipset 

• Compact module size for easy integration: 24x20x2.6 mm (0.94x0.79x0.10 in). 

• Fully automatic assembly: reflow solder assembly ready 

• Hardware compatible with SiRF GSWS 3 software 

• Multiple I/O pins reserved for customizing special user applications 

Performance 

• Cold/Warm/Hot Start Time: 42/38/8 Seconds for standard software under open-sky environment. 

• Reacquisition Time: 0.1 second. 

• RF Metal Shield for best performance in noisy environments. 

• Multi-path Mitigation Hardware. 

Interface 

• TTL level serial port for GPS communications interface 

• Protocol: NMEA-0183/SiRF Binary (default NMEA). 

• Baud Rate: User configurable from 4800 to 57600 baud (default 4800). 

• External command programmability 

Advantages 

• Ideal for high volume mass production 

• Cost saving through elimination of RF and board to board digital connectors 

• Flexible and cost effective hardware design for different application needs 

• Secure SMD PCB mounting method 

1


Recommended Design 

The Leadtek LR9805-III supports signal detection using an external active antenna. For optimum 

performance, Leadtek recommends that you use a 3.3V external active antenna with a built-in filter 

inside. 

The following diagram illustrates the recommended design for the LR9805-III using an active antenna 

and optional backup battery. For more information on the backup battery, see page 13. 

Active antenna 

3.3V antenna 

9805-III 

Backup 

Battery 

For more information or to order GPS related products, contact the Leadtek sales team at 

gps@leadtek.com. 

2

Specifications 


Technical Specifications 

Feature Item Description 

Chipset GSP3F Series SiRFstarIII technology 

General 

Frequency L1, 1575.42 MHz 

C/A code 

1.023 MHz chip rate 

Channels 20 

Accuracy 

Position 

10 meters, 2D RMS 

5 meters 2D RMS, WAAS corrected 


Environmental Characteristics 

Items 

Operating temperature range 

Storage temperature range 

Description 

-40 deg. C to +85 deg. C 

-55 deg. C to +100 deg. C 

Physical Characteristics 

Items 

Description 

Length 

24 mm (0.94in) 

Width 

20 mm (0.79 in) 

Height 

2.6 mm (0.1 in) 

Weight 2.5g 

Interface Specifications 

Items 

I/O 

Description 

28 pin SMD micro package 

4

Software 


SiRF GSW3 

The Leadtek LR9805-III module includes GSW3, the SiRF standard GPS software for SiRFstarIII 

receivers. Features include: 

• Excellent sensitivity 

• High configurability 

• 1-second position update rate 

• Supports use of satellite-based augmentation systems like the US WAAS or European EGNOS 

system 

• API compatible with GSW2 and SiRFLoc Client AGPS support 

• Real-time Operating System (RTOS) friendly 

• Capable of outputting both NMEA and SiRF-proprietary binary protocols 

• Designed to accept custom user tasks executed on the integrated ARM7TDM1 processor 

• Runs in full power operation or optional power saving modes (see page 19) 

GSW default configuration is as follows: 

Item 

Description 

Core of firmware SiRF GSW3 

Baud rate 4800 

Code type 

NMEA-0183 ASCII 

Datum 

WGS-84 

Protocol message GGA(1sec), GSA(5sec), GSV(5sec), 

RMC(1sec),VTG(1sec) 

Output frequency 1 Hz 

Acquisition Sensitivity Cold start 

30 dB-Hz (-143dBm) 

Warm start 

23 dB-Hz 

Hot start (Standard) 15 dB-Hz 

Tracking 

13 dB-Hz 

Options 

GSW3 software provides optional features when you require lower power consumption. These 

features include two optional power saving modes: 

• Trickle Power 

• Push-to-Fix 

For more information on these and other options, see page 19. 

5


TTFF Performance 

Test Setup 

To ensure consistent test results, the multi-channel GPS simulator is used with a signal attenuator to 

generate different signal strengths for the LR9805-III module. The generated signals are used to test 

the module’s TTFF and the tests are performed inside a noise-free chamber. See pages 7 and 8 for test 

results. 

6


Leadtek LR9805-III TTFF Test Results 

The following are TTFF test results using GSW3 software. 

Cold Start 

Time or location is unknown or hot or warm start failed. The following chart shows the Cold Start time 

in different signal strengths. 

Cold Start 

Time [Second] 

65 

60 

55 

50 

45 

40 

35 

30 

30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 

CN 

UNIT:Second 

Warm Start 

Time, location, and satellite almanac are available. The receiver has been powered off for more than 

two hours. The following chart shows the Warm Start time in different signal strengths. 

Warm Start 

55 

50 

Time [Second] 

45 

40 

35 

30 

26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 

CN 

UNIT:Second 

7


Snap Start 

Time, location, and satellite ephemeris are available. The receiver has been powered off for less than 

three minutes. Since last power-off, RTC is good. The following chart shows the Warm Start time in 

different signal strengths. 

Snap Start 

Time [Second] 

20 

19 

18 

17 

16 

15 

14 

13 

12 

11 

10 

9 

8 

7 

6 

5 

4 

3 

2 

1 

0 

16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 

CN 

UNIT:Second 

Hot Start 

Time, location, and satellite ephemeris are available. The receiver has been powered off for more than 

three minutes, but less than two hours. The following chart shows the Warm Start time in different 

signal strengths. 

Hot Start 

5 

Time [Second] 

4 

3 

2 

1 

0 

23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 

CN 

UNIT:Second 

8

Electrical Specifications 


Block Diagram 

RF Input 

GRF3W 

GSP 3F 

TTL 

Regulator 

IC 

TCXO 

Reset 

IC 

Flash 

ROM 

RTC 

X-tal 

LR9805-III-GPS Module 

Absolute Maximum Ratings 

Parameter Symbol Min Max Units 

Power Supply Voltage VCC_3V -0.3 3.6 V 

Input Pin Voltage VIN -0.3 5 V 

Output Pin Voltage VOUT -0.3 3.6 V 

Storage Temperature TSTG -55 100 ºC 

Operating Conditions 

Parameter Symbol Min Typical Max Units 

Power Supply Voltage VCC_3V 3.2 3.3 3.4 V 

Input Pin Voltage VIN 0 3.3 V 

Operating Temperature TOPR -40 85 ºC 

Operating Current ICC 65 65 70 mA 

Backup Battery Conditions 

Parameter Symbol Min Typical Max Units 

RTC(Battery) Power VSTBY 1.425 1.5 1.575 V 

Supply Current 10 µA 

9


DC Characteristics 

Parameter Symbol Min Max Units 

Input High Level Vih 2.0 ---- V 

Input Low Level Vil ---- 0.8 V 

Output High Level Voh 2.4 V 

Out Low Level Vol 0.4 V 

Input Leakage li 2 2 µA 

Current 

Input Capacitance 3 pF 

Output Capacitance 3 pF 

Bi-directional Buffer 

Capacitance 

3 pF 

10

Interface Specification 

Photos and Pin Positions 

Pin 28 

Pin 15 


Model number 

Serial number 

Pin Settings 

Pin 1 Pin 14 

PIN Name Type Description 

1 FREQ_XFER I If not used, keep floating 

2 NC I/O Not connected 


4 RXDB I TTL UART Port B input. If not used, keep floating 

5 RXDA I TTL UART Port A input 

6 TXDA O TTL UART Port A output 

7 GPIO5 I/O Reserved, keep floating 

8 TIMEMARK I/O 1 PPS timemark output 






14 GND PWR Ground 

15 VCC_IN PWR 3.3V supply input 

16 VSTBY PWR 

Apply 1.5V DC for backup RTC & SRAM. If not used, keep 

floating 

17 BOOTSEL I Pull high for programming mode. If not used, keep floating 

18 PBRESN I Reset pin, active low, If not used, keep floating 





23 TXDB O TTL UART Port B output. If not used, keep floating 

24 NC O Not connected 

25 ANTPWR PWR Antenna power input 


27 RFIN I RF Signal input 


11

Pin Functions 

Pin Name 

VCC_IN 

GND 

RXDA 

TXDA 

RXDB 

TXDB 

PBRESN 

TIMEMARK 

GPIO 

VSTBY 

BOOTSEL 

ANTPWR 

FREQ_XFER 

RFIN 


Description 

+3.3V power input. 

LR9805-III ground 

Serial input of Channel A (TTTL Level) 

Serial output of Channel A (TTTL Level) 

Serial input of Channel B (TTTL Level) 

Serial output of Channel B (TTTL Level) 

Provides active-low reset input to the board. Causes board to reset and start 

searching for satellites. PB Reset is an optional input and, if not utilized, it may 

be left open. 

1 PPS timemark output 

Reserved 

Battery backup supply reserved input 

Upgrading firmware, this pin should be active high 

Active antenna supply 

External clock input for SiRFLoc. See pg. 21 for more information. 

GPS RF signal input 

12


Backup Battery Design 

The backup battery provides power for the RTC and SRAM. Leadtek recommends that you use a 

battery backup to retain the data saved in SRAM when the VCC has been removed to ensure the 

continuous running of the RTC. With this feature, you do not have to wait for the cold start time to get 

a fix. If the information is saved in the SRAM, the satellite data will remain available for future access. 

The power input of the backup battery is 1.425V-1.575V through VSTBY. See page 11 for the pin 

setting. 

In the following reference design, a rechargeable backup battery is used with a voltage regulator. 

Reference Design 

Regulator 

1.5V 

To VSTBY (Pin 16) 

13

Mechanical Dimensions 


Outline Drawing 

(Unit : mm) 

14


Recommended PCB Layout 

(Unit : mm) 

15


Strip Line Layout 

The main purpose of the strip line is to reduce the impact due to impedance mismatch from return loss 

and propagation delay. The impedance of the strip line between the RF connector and 

LR9805-III (pin 27, RF_IN) must be maintained at 50 ohms. 

Reflow Profile 

High quality, low defect soldering requires identifying the optimum temperature profile for reflowing 

the solder paste. To have the correct profile assures components, boards, and solder joints are not 

damaged and reliable solder connection is achievable. Profiles are essential for establishing and 

maintaining processes. You must be able to repeat the profile to achieve process consistency. The 

heating and cooling rise rates must be compatible with the solder paste and components. The amount 

of time that the assembly is exposed to certain temperatures must first be defined and then maintained. 

The following is an example of a typical thermal profile. 

Peak Temperature 

Rate of 

Rise 

Wetting Time 

Preheat 

Dryout 

Reflow 

Cooling 

Notes 

• The equilibrium time can be adjusted to ensure that the out gassing of the flux is optimized 

• The equilibrium time can be increased if there is excessive voiding at PCB level 

• Solder composition: Sn 63%, Pb 37% 

Important features of profile 

• Initial Ramp = 60° C to 120° C/minute to 140°C to 150° equilibrium 

• Ramp to Maximum temperature (210°C to 215°) = 90°C to 120° C/minute 

• Time over liquids = 40 to 90 seconds 

16


Automated Manufacturing Components 

Reel Taping Specification 

• Material: Black Conductive High Impact Polystyrene Alloy (UP-6100) 

• Surface resistivity 10 9 – 10 12 Ω/□ 

• Quantity per reel: 1000 pcs./reel 

(Unit : mm) 

Tape Reel Drawing 

17


Polystyrene Alloy Taping Specifications 

• 10 sprocket hole pitch cumulative tolerance ±0.20mm 

• Carrier camber is within 1mm in 250mm 

• A0 and B0 measured on a plane 0.3mm above the bottom of the pocket 

• K0 measured from a plane on the inside bottom of the pocket to the top surface of the carrier 

• Material: black anti-static polystyrene alloy 

• All dimensions meet EIA-481-3 requirements 

• Thickness: 0.50±0.05cm 

• Packing length per 22” reel: 50.0 Meters (1:2) 

• Component load per 15” reel: 1000 pcs. (SUR-56-3-XL) 

Polystyrene Alloy Taping Drawing 

Ordering Information 

For every order of 1000 pcs , Leadtek will ship the modules with the reel package (shown on page 17). 

For order quantities less than 1000 pcs, or when ordering non-whole numbers, Leadtek will snip the 

taping and ship the quantity that you request without the reel. 

To place an order, contact gps@leadtek.com. 

18


Appendix A 

Software Options 

Trickle Power Mode 

The LR9805-III design includes all the functionality necessary to implement the SiRF Trickle 

Power mode of operation. In this mode, the lowest average power dissipation is achieved by 

powering down the board (after a position is determined) in such a manner that when it is turned back 

on it can recompute a position fix in the shortest amount of time. Standard Trickle Power operates in 

these states: 

• Tracking State 

In this state, the board is fully powered, tracking satellites, and gathering data. 

• CPU State 

In this mode, the GPS radio frequency (RF) front end can be partially powered down at the end of 

the tracking state through pin control. This mode allows the continued output of the clock to the 

baseband chip, while powering down all other internal RF circuits in the GPS RF front end. The 

CPU would keep running to process the GPS data until a position fix is determined and the result 

has been transmitted by the serial communication interface. 

• Trickle State 

At the end of the CPU state, the entire RF section is shutdown completely through control of the 

RF voltage regulator shutdown pin. In this state, the CPU is in a low power standby state and the 

receiver clocks are off with only the RTC clock active. After a set amount of time, the RTC 

generates a NMI signal to wake up the CPU and reset the receiver back to the tracking state. 

Push-to-Fix Mode 

The Push-to-Fix mode puts the receiver into a background duty cycle function that provides a periodic 

refresh of position, GPS time, ephemeris data, and RTC calibration every 30 minutes. The Push-to-Fix 

mode is similar but exclusive from the Trickle Power mode, meaning that only one mode can be set at 

a time. The purpose of the Push-to-Fix mode is to support applications where a position fix is only 

required when you request it, or the application requests it. The Push-to-Fix mode puts the receiver in 

the Trickle state until commanded to generate a fix. Push-to-Fix operates in these states: 

• Power-on State 

In this state the receiver calculates the position once, collects the ephemeris, and calibrates the 

RTC before going back to the Trickle state. 

• Trickle State 

In this state only the RTC is running. The supply current is typically less than 500uA, which 

includes the standby current of the baseband IC. 

There are three events that can happen, which effectively return the CPU to normal operation: 

• Power-on: If power is removed then re-applied to the board, a reset signal is generated by the 

CPU supervisor. After the reset has been removed, the CPU will start up, get a fix and return to 

Trickle state. This typically takes two to six seconds. 

19


• Ephemeris Collection: Every 30 minutes the receiver wakes up the CPU to calculate a fix, 

collect a new ephemeris, calibrate the RTC, and then go to the Trickle State. 

• User Requested Fix: When you request of a fix, the CPU will wake up by toggling PBRES 

low (interface pin 18). The CPU is restarted and (following a Snap Start) a fix is calculated. 

Before going back to the Trickle State, the CPU will check the ephemeris and the RTC 

calibration. 

Note: The CPU will restart within 200-600 ms after the PBRES input is brought high. 

Average Current for GPSCLK Trickle Power, 200msec On Time 

Item Current(mA) Time (ms) 

Update Period 1 --- 1080 6000 10080 

Tracking State 73 280 280 280 

CPU State 2 41.5 260 260 260 

Sat Positioning 3 41.5 600 700 700 

Trickle State 4 3.4 540 4760 8840 

Average Current (mA) --- 30.6 12.7 9 

Average Power (mW) --- 101 41.9 29.7 

Dead Reckoning 

SiRFDRive is a closely coupled Dead Reckoning option that can be supported by Leadtek LR9805-III. 

This option allows the navigation system to accept inputs from low cost heading rate sensors and 

vehicle speed wheel ticks in order to compute dead reckoning positions when GPS signals are blocked 

or degraded. 

With SiRFDrive, the dead reckoning information is incorporated into the main navigation software 

filter through patented close coupling algorithms, instead of functioning independently from the GPS 

part of the system. This improves accuracy and reliability of position fixes. GPS measurements 

calibrate the dead reckoning sensors to ensure optimum speed and heading accuracy. Dead reckoning 

measurements validate and correct GPS fixes during signal blockage and multi-path providing you 

with navigation that is continuous and reliable. 

Contact your SiRF representative directly for more information about this feature. 

1 Update Period is greater than programmed value by approximately 80-100 ms. 

2 With all development data messages turned on the CPU state time increases. 

3 Satellite positioning task occurs during CPU state once per 6 second interval. With one second update interval, the 

satellite positioning task takes about 100 ms less, since it uses the available throughput during the following task state. 

4 Total Trickle state time computed over a 6 second interval for 1000 and 6000 ms update period and over 10 second 

interval for 10000 ms update period. 

20


SiRFLoc A-GPS Client Software 

Leadtek LR9805-III with TCXO design supports SiRFLoc MultiMode Aided-GPS (A-GPS) 

technology for Location Based Service (LBS) applications. The MultiMode A-GPS software supports 

multiple positioning methods and is adaptable to work with aid available on the network. Contact your 

SiRF representative directly if you want to use LR9805-III with SiRFLoc Client, together with 

SiRFLoc Server for a complete end-to-end A-GPS solution. 

GMonitor Software 

GMonitor is a software program used to test and view performance of GPS receivers. It is used with 

Leadtek evaluation kits (EVKIII) to test SMD module performance. For more information about 

GMonitor, see the GMonitor User’s Guide. 

21

Glossary 


A-GPS 

Assisted GPS or AGPS is a technology that uses an assistance server to cut down the time needed to 

find the location. Although GPS provides excellent position accuracy, position fixes require lines of 

sight to the satellites. In regular GPS networks there are only GPS satellites and GPS receivers. 

In A-GPS networks, the receiver, being limited in processing power and normally under less than ideal 

locations for position fixing, communicates with the assistance server that has high processing power 

and access to a reference network. Although dependent on cellular coverage, AGPS processing is 

quicker and more efficient than regular GPS. 

API 

An application programming interface is a set of definitions of the way one piece of computer software 

communicates with another. One of the primary purposes of an API is to provide a set of commonly 

used functions, such as to draw windows or icons on the screen. Programmers can then take advantage 

of the API by making use of its functionality, saving them the task of programming everything from 

scratch. 

Baud Rate 

Is a measure of the signaling rate, which is the number of changes to the transmission media per 

second in a modulated signal. 

For Example: 250 baud means that 250 signals are transmitted in one second. If each signal carries 4 

bits of information then in each second 1000 bits are transmitted. This is abbreviated as 1000 bit/s. 

Dead Reckoning 

The process of estimating your position by advancing a known position using course, speed, time and 

distance to be traveled. It is figuring out where you will be at a certain time if you hold the speed, time 

and course you plan to travel. 

Differential GPS (DGPS) 

An extension of the GPS system that uses land-based radio beacons to transmit position corrections to 

GPS receivers. DGPS reduces the effect of selective availability, propagation delay, etc. and can 

improve position accuracy to better than 10 meters. 

EGNOS 

A satellite navigation system being developed by the European Space Agency, the European 

Commission, and EUROCONTROL. It is intended to supplement the GPS and GLONASS systems by 

reporting on the reliability and accuracy of the signals. According to specifications, horizontal position 

accuracy should be better than 7 meters. In practice, the horizontal position accuracy is at the meter 

level. It will consist of three geostationary satellites and a network of ground stations. 

Similar service is provided in America by the WAAS system. See WAAS. 

22


European Geostationary Navigation Overlay System 

See EGNOS. 

LNA 

A special type of electronic amplifier or amplifier used in communication systems to amplify very 

weak signals captured by an antenna. It is usually located at the antenna and is a key component, which 

is placed at the front-end of a receiver system. 

Low Noise Amplifier 

See LNA. 

Multi-path mitigation 

Anticipating errors caused when a satellite signal reaches the GPS receiver antenna by more than one 

path. Usually caused by one or more paths being bounced or reflected off of structures near the 

antenna and occurs to some extent everywhere. The signal which traverses a longer path will yield a 

larger pseudo range estimate and increase the error. 

NMEA 

An U.S. standards committee that defines data message structure, contents, and protocols to allow the 

GPS receiver to communicate with other pieces of electronic equipment. 

National Marine Electronics Association 

See NMEA. 

1PPS 

Pulse which is generated once per second. GPS and some radio clocks and related timekeeping gear 

have a pulse-per-second or PPS signal that is needed for high accuracy time synchronization. The PPS 

signal can be connected in either of two ways, either through the data leads of a serial port or through 

the modem control leads. Either way requires conversion of the PPS signal, 

Most GPS devices emit an rs-232 serial stream with some kind of timestamp format. Many GPS 

devices are small realtime systems with the satellite tracking done at high priority, positioning done at 

medium priority, and time output done at low priority. The timestamps often have +- 200 ms of jitter 

(variance in delay), and output a PPS signal on the exact second. 

SMD 

Electronic device components that are mounted directly onto the surface of printed circuit boards 

(PCBs). In the industry it has largely replaced the previous construction method of fitting components 

with wire leads into holes in the circuit board (also called through-hole technology). 

Surface Mount Device 

See SMD. 

23


TCXO 

An electronic device that uses the mechanical resonance of a physical crystal to create an electrical 

signal with a very precise frequency and can be embedded in integrated circuits. TCXO reduces the 

environmental changes of temperature, humidity, and vibration, to keep a stable output frequency. 

Temperature Controlled Crystal Oscillator 

See TCXO. 

Time To First Fix (TTFF) 

The time it takes a GPS receiver to find satellites after you first turn it on, when the GPS receiver has 

lost memory, or has been moved over 300 miles from its last location. Standard TTFF Timing consists 

of: 

Mode Requires Timing 

Snap Start Hot + Clock + Sat Pos 3 minutes off 

Hot Start Warm + Ephemeris 30 minutes off 

Warm Start 

Position Accuracy 

Time Accuracy 

Almanac 

Cold Start Nothing N/A 

Leadtek Research Inc. 

18F, 166, Chien-Yi Rd., 

Chung Ho, Taipei Hsien, 

Taiwan (235) 

©2006 Leadtek Research, Inc. 

All rights reserved. 

Version 1.4 

3/06

Interface Specifications - Standard ICs

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