GB2380343A

GB2380343A - Locating system having a GPS receiver combined with a mobile phone

Info

Publication number: GB2380343A
Application number: GB0111973A
Authority: GB
Inventors: Richard Pulham
Original assignee: Individual
Current assignee: Individual
Priority date: 2001-05-16
Filing date: 2001-05-16
Publication date: 2003-04-02
Also published as: GB0111973D0

Abstract

A locating system having a GPS receiver coupled to a mobile telephone communicates with a central computer though a telephone network. The central computer establishes the general location of the mobile telephone and transmits assistance data though the mobile telephone to the GPS receiver. The assistance data enables selection of the appropriate satellites for position determination. Positional data is obtained by the GPS receiver and transmitted to the central computer. The general location of the mobile telephone may be the location established when the telephone was last used. The positional data may be delivered to the central computer by SMS.

Description

1 Introduction This report describes the design of the SMS/GPS Technology Demonstrator Unit developed for CGL Technology Ltd, hereafter referred to as the TDU.

The TDU is connected to a GSM handset (mobile phone) and enables a user to report his/her position to a remote station with a single button push.

The TDU continuously reads position information from its internal Global Positioning System (GPS) receiver. When the button is pressed the TDU uses the host GSM handset to send its position, in longitude and latitude format, as a text message to a pre-programmed

telephone number using the Short Message Service (SMS). This is depicted in

Figure (general Arrangement.

\

The TDU is designed specifically for use with a Panasonic GD70 handset.

According to the present invention there is provided a demonstrator which revolves around the initialisation process.

According to the present invention there is provided a system using a mobile phone as a link to a central computer which can then feed back navigation data to the mobile phone on a piecemeal basis.

2 Handling The TDU is a prototype electronic equipment. It contains hand built, discretely wired circuits rather than the more rugged printed circuit boards that would be used in a production version. The TDU should be considered fragile and handled with care.

The TDU contains electrostatic discharge (ESD) sensitive devices and should be opened only by qualified personnel at an ESD protected workstation.

3 Instructions for Use

The following instructions explain how to use the TDU. Fi17l1il) Front Panel and Fis) Side Panel show the controls, indicators and connectors on the TDU -- 3.1 To send position > connect the TDU to the GD70 handset using the supplied interconnect lead > switch on the GD70 > wait for the GD70 to find the network (ready to make calls) > switch on the TDU > observe the red diagnostic indicator-it will flash at a rate of 0.25 to 1. 0Hz indicating that the TDU is functional > observe the green"GPS acquired"indicator : tfit is illuminated the GPS is receiving updated positions every second and the current position of the TDU will be transmuted If the green led fails to illuminate, the GPS receiver does not have an up-to-date position and the last known position will be transmitted.

> press the"Send Position"push-button : the position will be sent to the receiving stamen as an SMS call. During the call the red diagnostic indicator will cease flashing. There is no indication on the GD70 that the call is being made. z once the position message has been sent the red diagnostic indicator will resume Basting 3.2 To Charge TDU Battery The primary source of power for the TDU is a 500mAh 6V NiMH rechargeable battery pack. The battery pack provides power for approximately 2.5 hours from fully charged. The GPS receiver is the dominant load on the battery, drawing 120mA. To conserve battery power, switch on the TDU only when a position transmission is to be made.

The TDU may be powered from an auxiliary 6Vdc supply in the event that the battery is allowed to discharge completely. Note that the battery is not charged by the auxiliary supply.

The TDU battery pack is trickle charged with a standard NiCd charger. The time to fully chargethe battery is 14 hours at 50mA. The TDU is not operational during charging.

The low battery indicator illuminates when the battery has approximately 1.5 hours life remaining and as such is not currently a reliable indicator of imminent battery failure. This shortcoming is attributable to the specific cells used in the battery pack which charge to 1. 1 V rather than 1.2V, the cell voltage

expected from NiMH. It is envisaged that cells obtained from a different manufacturer would remit in the low battery indicator operating correctly and illuminating with 0.5 hours operation remaining- 3.3 To Charge GPS Receiver Internal Lithium Battery The GPS receiver in the TDU contains a rechargeable lithium battery that backs up memory containing satellite almanac data. The lithium battery is trickle charged whenever the TDU is switched on If the lithium battery is allowed to fully discharge the almanac data will be lost and the GPS receiver will have to search the sky every tune it is switched on. This will result in an increase in time to obtam a valid fix to 5 to 10 minutes.

In order to ensure that the lithium battery does not become fully discharged the TDU should te powered on for a period of at least 30 minutes every month while the GPS receiver has a Palidffx.

4 Functional Description 4.1 GPS Receiver Functions The GPS receiver, a Garmin GPS35, is a complex unit that acquires signals from the GPS satellites, via its own integral antenna, applies a complex processing algorithm and calculates the position of the unit in terms of longitude and latitude. It calculates position once per second and transmits this information as an ASCH string (NMEA sentence $LCGLL) to the microcontroller. The data transmitted also contains a field indicating whether the GPS receiver has been able to calculate a valid position given the prevalent signal reception conditions. If a valid fix is unobtainable the position data sent is that of the last known good position.

4.2 Microcontroller Functions The microcontroller receives position data from the GPS receiver and stores it in memory. It illuminates the"GPS acquired"indicator if the position is valid. The microcontroller also monitors the state of the"send position"push-button. When it senses that the button has been depressed it: > Converts the current position data to a format suitable for transmission over the GSM SMS system (PDU mode formatting) > Initialises the mobile phone > Sends the position data, in the form an SMS text message, to the preprogrammed telephone number.

> Note that the telephone number to which the position message is sent is programmed into the microcontroller's memory, not the mobile phone's

5 Hardware Description The following description of the hardware design refers to the hardware block diagram shown in Figure 5-1 Hardware Block Diagram.

5.1 Battery Pack The battery pack comprises five AAA 500mAh NiMH cells connected in series giving an output voltage of 6V. NiMH is used in preference to NiCd due to its higher capacity/volume ratio and reduced memory effect. When the battery charger is plugged into the TDU the battery is automatically disconnected from the TDU through the action of the charger input socket.

5.2 Regulator The 6V supply from the battery is regulated to +5V by a Maxim MAX667 micropower voltage regulator. A micropower device was selected to minimise battery loading. This device also has an inbuilt low battery detector. As the battery voltage drops, the regulator drop-out voltage reduces.

When the regulator is no longer able to regulate the low battery indicator is asserted and used to illuminate an LED on the front panel.

The regulated 5V supply powers the GPS receiver, microcontroller and ancillary electronics.

5.3 GPS Receiver The GPS receiver is a Garmin GPS35-LVS. This is a fully integrated device, including an antenna, intended for use in OEM equipment applications. The LVS variant is powered from +3.6V to +6. 0V and communicates with the host system via an RS232 asynchronous communications link.

Prior to installation the GPS35 is programmed, using the $PGRMO command to transmit only SPGRMT, $LCGLL and $GPRMC sentences at 4800 baud. The RS232 communications line can be broken by removing wire links LK3 and LK4. The GPS35 can then be connected to a PC serial port and an RS232 terminal program (such as Hypertyerminal) used to communicate with it.

The technical specification for the GPS35 is included as an appendix to this report.

5.4 Oscillator An oscillator circuit with 3. 6864MHz crystal provides the master clock signal to the microcontroller and SPI UART. The selection of 3. 6864MHz provides: * a relatively low microcontroller operating speed, which conserves battery power whiles providing sufficient processing power . a convenient frequency source for the baud rate generators on the microcontroller and SPI UART 5.5 Reset Power on reset is automatic. Reset can be asserted manually by depressing a push-to-make switch connected across the reset header pins. A power up timer in the microcontroller is enabled at programming time. The power up timer holds off the internal microcontroller reset for 74mS after the +5V supply has settled, ensuring sufficient time for the oscillator to stabilise.

5.6 SPI UART The SPI UART is a Maxim MAX3100.

It is included to provide a duplex asynchronous communications port to the GD70 phone (the microcontroller has just one UART and this is used to communicate with the GPS receiver). The microcontroller in turn communicates with the MAX3100 via an SPI link. It uses this link to configure and control the MAX3100. Messages to the phone are passed from the microcontroller to the MAX3100 for onward transmission. When the MAX3100 receives a character from the phone it

asserts the microcontroller interrupt ; the microcontroller then interrogates the MAX3100 and retrieves the character.

The command set used by the microcontroller to communicate with the MAX3100 is specified in the MAX3100 datasheet this is included in an appendix to this report for reference.

Communications between the MAX3100 and the phone are at 9600 baud.

5.7 Microcontroller The microcontroller is a Microchip PIC16C76JW. This is an 8-bit mid-range microcontroller with the following features : 20MHz max operating frequency 8kbytes onboard EPROM

364 bytes onboard RAM- UART SPI port 2 timers miscellaneous I/O ports The software is programmed into the onboard EPROM. Onboard RAM is used for data storage: RAM usage is approximately 90%.

5.8 RS232 Transceiver A MAX220 is used to translate CMOS logic levels to/from the microcontroller into RS232 levels to/from the GPS receiver. It also provides translation to RS232 levels of the CMOS signals between the SPI UART and GD70 phone. These RS232 signals are available on test connectors so that they can be monitored, for development and debugging purposes, on a PC running a terminal program (eg Hyperterminal).

5.9 GPS Acquired Indicator This is a green LED on the front panel that is illuminated by the microcontroller whenever the GPS has a valid fix i. e when the"V"flag inNMEA sentence $GPRMC reported by the GPS receiver is set.

5.10 Diagnostic Indicator This is a red led mounted on the front panel used for various purposes to aid diagnostics during development : these include, 'toggle each time a SGPRMC sentence is received from the GPS receiver * a burst of 5 quick flashes if an error occurs during the send position message sequence When communicating with the GD70 phone the diagnostic indicator ceases flashing unless an error occurs. Flashing resumes when the phone call is complete.

6 Software Description The software flow of control is shown in the following series of diagrams. Functions shown in bold type are in turn represented by a lower level flow diagram. Comments are included to aid in describmg the general structure of the software.

These flow diagrams should be read in conjunction with: * The source code, which is commented extensively . Panasonic EB-G600/GD, 70 AT Command Functional Command Specification, for details of communications flow to and from the phone 'Siemens"SMS with the SMS PDU mode Developers Guide"and GSM03. 38 for details of PDU data format

Abbreviations CMOS Complementary Metal Oxide Silicon EPROM Erasable Programmable Read Only Memory GSM Global System for Mobile communications GPS Global Positioning System I/O Input/Output LED Light Emitting Diode NMEA National Marine Electronics Association RAM Random Access Memory SMS Short Message Service SPI Synchronous Peripheral Interface TDU Technology Demonstrator Unit UART Universal Asynchronous Receiver/Transmitter

1. Introduction To use the SMS you have to declare the number of the SMSC' (Short Message Service Center) in the MS (Mobile Station), provided that the MS support SMS-MO (Short Message Service-Mobile Orginated).

The SIEMENS S25, SL10, S10, S10 active, EI0, Ml Module for example are providing SMS-MO.

card SMSC-number (Germany) D1 491710760000 D2 491722270000

At the MOBILE you enter the SMSC-number with the AT+Celular command : at+csca =" < SMSC-number > " If the receiver of the SMS possesses a D2 card, the AT command has to be entered in the following way: at+csca ="+491722270000"

( With the command at+csca? you can question the actual adjusted SMSC-number Ask your network operator for the right SMSC-number ! ! ! notice : In addition to the AT+CSCA command it is possible to enter The SMSC- number in front of the Protocol Data Unit (PDU) see chapter 3.1 !

The MMI is based on the command set of AT+Cellular, and could be realized by means of a terminal (for example Triodata, Telix, WIN-Terminal) or the display of a handy.

The SM-TL provides a service to the Short Message Application Layer. This service enables the SM-AL to transfer short messages to its peer entity, receive short messages from its peer entity and receive reports about earlier requests for short messages to be transferred.

The SM-TL communicates with its peer entity with six several PDUs (Protocol Data Units): * SMS-DELIVER, conveying a short message from the SMSC to the MS 'SMS-DELIVER-REPORT, conveying a failure cause (if necessary) * SMS-SUBMIT, conveying a short message from the MS to the SMSC * SMS-SUBMIT-REPORT, conveying a failure cause (if necessary) * SMS-STATUS-REPORT, conveying a status report from the SMSC to the MS * SMS-COMMAND, conveying a command from the MS to the SMSC The SMS-DELIVER and SMS-SUBMIT PDUs are described in the following sections.

2. 1 SMS-DELIVER (Mobile Terminated)

2.2 SMS-SUBMIT (Mobile Originated)

! notice: Any unused bits will be set to zero by the sending entity and will be ignored by the receiving entity!

SCA Service Center Adress - Telephone number of the Service Center information element PDU Type Protocol Data Unit Type MR Message Reference sucessive number (0.. 255) of all SIS-SUBMIT Frames set by the MOBILE OA Originator Adress Adress of the onginating SME DA Destination Adress Adress of the destination SME PID Protocol Identifier Parameter showing the SMSC how to process the SM (as FAX, Voice etc) DCS Data Coding Scheme Parameter identifying the coding scheme within the User Data (UD) SCTS Service Center Time Parameter identifying time when the SMSC Stamp received the message VP Validity Period Parameter identifying the time from where the message is no longer valid in the SMSC UDL User Data Length Parameter indicating the length of the t field UD User Data Data of the SM RP Reply Path Parameter indicating that Reply Path exists UDHI User Data Header Parameter indicating that the UD field contains a Indicator header SRI Status Report Indication Parameter indicating if the SME has requested a status report SRR Status Report Request Parameter indicating if the MS has requested a status report VPF Validity Period Format Parameter indicating whether or not the VP field is present MMS More Messages to Send Parameter indicating whether or not there are more messages to send RD Reject Duplicate MTI Message Type Indicator Parameter describing the message type 00 means SMS-DELIVER 01 means SMS-SUBMIT

3. Parameter description 3. 1 Service Center adress information element (SCA info element)

len : The octet en"contains the number of octets reqiured for the number of the Service Center plus the 1 byte, type of number" type of number: 81H : the following number is national 91H : the following number international (for further information see GSM 04.08 chapter 10.5. 4.6) octet: One octet includes two BCD-digit Fields If the called party BCD number contains an odd number of digits, the last digit shall be filled with an end mark coded as''FIr' Example: if you have the SC-number +49 171 0760000 you have to type : 0791947101670000 ! notice : If the Ien"field is set to Zero the MOBILE takes the default value of the Service Center adress set by the AT+CSCA command! 3.2 Protocol Data Unit Type (PDU Type)

! notice: you have to write the PDU-type in Hex-Format, a possible example is"11H" ! RP: 0 Reply Path parameter is not set in this PDU 1 Reply Path parameter is set in this PDU

UDHI: 0 The UD field contains only the short message 1 The beginning of the UD field contains a header in addition of the short message SRI: (is only set by the SMSC) 0 A status report will not be returned to the SME 1 A status report will be returned to the SME SRR: 0 A status report is not requested 1 A status report is requested VPF: bit4 bit3

0 0 VP field is not present 0 1 Reserved 1 0 VP field present an integer represented (relative) 1 1 VP field present an semi-octet represented (absolute) any reserved values may be rejected by the SMSC MMS: (is only set by the SMSC) 0 More messages are waiting for the MS in the SMSC 1 No more messages are waiting for the MS in the SMSC RD: 0 Instruct the SMSC to accept an SMS-SUBMIT for an short message still held in the SMSC which has the same MR and DA as a previosly submitted short message from the same OA.

1 Instruct the SMSC to reject an SMS-SUBMIT for an short message still held in the SMSC which has the same MR and DA as a previosly submitted short message from the same OA.

MTI: bitl bitO Message type 0 0 SMS-DELIVER (SMSC > MS) 0 0 SMS-DELIVER REPORT (MS = > SMSC, is generated automatically by the MOBILE, after receiving a SMS-DELIVER) 0 1 SMS-SUBMIT (MS > SMSC) 0 1 SMS-SUBMIT REPORT (SMSC > MS) 1 0 SMS-STATUS REPORT (SMSC > MS)

1 0 SMS-COMMAND (MS = > SMSC) 1 1 Reserved (the fat-marked lines represent the features supported by the MOBILE) ! notice: not every PDU Type is supported by the Service Center ! 3.3 Message Reference MR

The MR field gives an integer (0.. 255) representation of a reference number of the SMSSUBMIT submitted to the SMSC by the MS.

! notice: at the MOBILE the MR is generated automatically,-anyway you have to generate it-

a possible entry is for example"OOH" ! a possi 3.4 Originator Adress OA Destination Adress DA OA and DA have the same format explained in the following lines:

len : The octet'en"contains the number df BCD digits type of number: 81H: the following number is national 91H : the following number international (for further information see GSM 04.08 chapter 10.5. 4.6) BCD-digits: The BCD-digit Field contains the BCD-number of the Destination e. g. of the Originator If the called party BCD number contains an odd number of digits, the last digit shall be filled with an end mark coded as"FH" Example: if you have the national number 1234567 you have to type: 0781214365F7 3.5 Protocol Identifier PID

The PID is the information element by which the Transport Layer either refers to the higher layer protocol being used, or indicates interworking with a certain type of telematic devicehere are some examples of PID codings: OOH : The PDU has to be treat as a short message 41H : Replace Short Message Typel 42H : Replace Short Message Type2 43H : Replace Short Message Type3

......

47H: Replace Short Message Type7 If replace Short Message Type x"is present, then the MS will check the associated SC address and originating address and replace any existing stored message having the same Protocol Identifier code, SC address and originating address with the new short message and other parameter values. If there is no message to be replaced, the MS shall store the message in the nonnal way.

(for further information see GSM 03.40 chapter 9. 23. 9) ! notice : it is not guaranteed that the SMSC supports every PID codings! 3.6 Data Coding Scheme DCS

The DCS field indicates the data coding scheme of the UD (User Data) field, and may indicate a message class. the octet is used according to a coding group which is indicated in bits 7.. 4.

The octet is then coded as follows:

Coding group : bits 7..4 bits 3..0

0000 Alphabet indication Unspecified message handling at the MS 0000. Default alphabet (7 bit data coding in the User Data) 0001-1111 reserved 0001-1110 Reserved coding groups 1111 Data Coding/message class bit 3 is reserved, set 0 bit 2 (message coding) 0 Default alphabet (7 bit data coding in the User Data) 1 8-bit data coding in the User Data bit MtO (message class) 0 0 Class0 immediate display 0 1 Class ! ME (Mobile Equipmeat) - specific 1 0 Class2 SIM specific message 1 1 Class3 TE (Terminate Equipment)- specific Default alphabet indicates that the UD (User Data) is coded from the 7-bit alphabet given in the appendix. When this alphabet is used, eight characters of the message are packed in seven octets, and the message can consist of up to 160 characters (instead of 140 characters in 8-bit data coding) In 8-bit data coding, you can relate to the INTEL ASCH-HEX table.

In Class 0 (immediate display) the short message is written directly in the display, as the Ml has no display the Class 0 message can be realised only in a roundabout way.

! n Class 1 to Class 3 the short message is stored in the several equipments ME, SIM-card and TE.

In time the Class 2 is supported, if you choose Class 1 or Class 3 the short message is treated the same way as a Class 2 message.

! note : It is recommended to use the Class2 message, or the coding group "0000 biD" ! 3.7 Service Center Time Stamp SCTS The SCTS is the information element by which the SMSC informs the recipient MS about the time ofanival of the short message at the Transport Layer entity of the SMSC. The time value is included in every SMS-DELIVER being delivered to the SMSC, and represents the local time in the following way:

The Time Zone indicates the difference, expressed in quarters of an hour, between the local time and GMT (Greenwich Main Time).

3. 8 Validity Period VP The Validity-Period is the information element which gives an MS submitting an SMSSUBMIT to the SMSC the possibility to include a specific time period value in the short message. The Validity Period parameter value indicates the time period for which the short message is valid, i. e. for how long the SMSC shall guarantee its existence in the SMSC memory before delivery to the recipient has been carried out.

The VP field is given in either integer or semi-octet representation. In the first case, the VP comprises 1 octet, giving the length of the validity period, counted from when the SMSSUBMIT is received by the SMSC. In the second case, the VP comprises 7 octets, giving the absolute time of the vality period termination.

In the first case, the representation of time is as follows :

VP Value Validity period value 0-143 (VP + 1) x 5 minutes (i. e 5 minutes intervals up to 12 hours) 144-167 12 hours + ( (VP-143) x 30 minutes) 168-196 (VP-166) x 1 day 197-255 - 192 x 1 week in the second case, the representation of time is identical to the representation or the SCTS (Service Center Time Stamp) The case of representation is set in the VPF (Validity Period Format) in the PDU-type.

3.9 User Data Length UDL and User Data UD

I The UDL field gives an integer representation of the number of characters within the User Data field to follow.

4. PDU Examples

.-ors IIR DCS Plu tHX. Ptd 0011000781214365F70000AA05E8329BFD06.

-'"') < (. ! < Hxaft OM (in ) oftA < mM : {U0t.} tM) M) tt) t) haba)) t Dos* & NWnAdiw & -UDL dwl*A awmo* I ILI r bw PID DCS ,"' j*..," (M* "of PDUnwraw too PID ms WA (-, 491-MO ? 600" 0791M7tM6700000ob7M. 214365F7boF6A 0568656C6C6F UDrheM- eM J 237)) " H ASO.

(four days) MrD (*Wdml

here are two examples how to send a short message with AT+CeMatar : first enter PIN-number and the Service Center Adress : +cpilF"wsr enter the < nanber Nt="XXXy"eotereJW-MMH & er OK eetc < =''+MZM7MM"eer < e & rvMe-Ceer-d ! reM ere D OK , Ist examPle : a < cm=7 : : ]4fJ enter "send message ". 140 is the maximum length (in hyte) ofthefollowing PDU > CO1MC78121436SF700AMMJ29BFP6 type PDt/(SMS-SUBA) aninish wtth"clrl Z"the thin-typed characters are the Destination Adress e. g. the own tet-number the Service Center adess is tin same as set via at+csco command

OK

alms ? are messages stored on the SIM-Card ? +CPMS :"SM", !, 7,"SM", t, 7 on this 81M-Card is 1 message stored OK you can store at most 7 messages at+emgr=y read stored message in location I +CMGR: 0.. 24 00040C9194718215219200006930824161840005E8329BFD06 This is a PDU (SMS-DELIVER) sent by the Service Center OK 2nd example :

at+cmgw=140 write message in the memory of the SIM-card > 07919M767000011000781214365F70OF6AAM6C6F type the DDU (SMS-SUBM/7 ? andfinish with"ctrl Z"the thin-typed characters are the Destination Adress e. g. the own tel-number. The Service CeMfdireM & +4P7770760000" +CMGW : 2 OK at+cmgr=2 read stored message in location 2 +CMGR: 2.. 17

OO1l000781214365F700F6AA0568656C6C6F this is the PDU stored in location 2 OK < +CMM== jeft e meMae ore < /w/oea oM 2 +CMSS : 3 OK at+cmss=2,"7654321",129 send the message stored in location 2 to the national

(129 = N7 na/ton are., 7o2/" at+cmss=2 :'+491717654321", 145 send the message stored in location 2 to the international =P/t) Mona < reM.. +P77776J27" at+cpms ? are messages stored on the SIM-Card ? +CPMS :"SM", 3, 7,"SM", 3,7 on this SIM-Card are 3 message stored OK you can store at most 7 messages at+cmgr=3 read stored message in location 3 +CMGR: 0.. 24 00040C9194718215219200F6693082519472000568656C6C6F This is a PDU (SMS-DELIVER) sent by the Service Center OK

5. Appendix Default alphabet :

b7 0 0 0 0 1 1 1 1 b6 0 0 1 1 0 0 1 1 b5 0 1 0 2 0 1 0 1 b4 b3 b2 b1 0 1 2 3 4 5 6 7 0 0 0 0 0 &commat; # SP 0 - P - P 0 0 0 1 1 ! ! A O a q 0 0 1 0 2 $ # " 2 B R b r 0 0 1 1 3 # &num; 3 C S c s 0 1 0 0 4 # 4 D T d t 0 1 0 1 5 # % 5 e u E U 0 1 1 0 6 # & 6 F V f v 0 1 1 1 7 # ' 7 G W g w 1 0 0 0 8 # ( 8 H X h x 1 0 0 1 9 # ) 9 I Y i y 1 0 1 0 10 LF # * : J Z j z 1 0 1 1 11 + ; K Ä k ä 1 1 0 0 12 , < L Ö l ö 1 1 0 1 13 CR - = M m 1 1 1 0 14 ss . > N Ü n ü 1 1 1 1 15 / ? O o abbreviations : MS Mobile Station SME Short Message Entity SMSC Short Message Service Center um Man Machine Interface PDUs Protocol Data Units SM-AL Short Message Aplication Layer SM-TL Short Message Transport Layer SM-RL Short Message Relay Layer SM-LL Short Message Link Layer PDU Type Protocol Data Unit Type MR Message Reference OA Originator Adress DA Destination Adress PID Protocol Identifier DCS Data Coding Scheme SCTS Service Center Time Stamp VP Validity Period UDL User Data Length UD User Data RP Reply Path UDHI User Data Header Indicator SRI Status Report Indication SRR Status Report Request VPF Validity Period Format MM8 More Messages to Send RD Reject Duplicate MTI Message Type Indicator ME Mobile Equipment TE Terminal Equipment SIM Subscriber Identity Modul

error codes: 0 phone failure 1 no connection to phone 2 Phone-adaptor link reserved 3 operation not allowed 4 operation not supported 5 PH-SIM PIN necessary 10 SIM not inserted 11 8IM PIN required 12 SIM PUK required 13 SIM failure 14-SIM busy 15 SIM wrong 16 incorrect password 20 memory full 21 invalid index 22 not found 23 memory failure 24 text string too long (+CPBW) 25 invalid characters in text string 26 dial string to long 27 invalid characters in dial string 30 no network service 31 network timeout 100 unknown 265 PUK for theft protection necessary 266 PUK2 for SIM necessary 267 PIN2 for SIM necessary

1 Scope This technical specification defines the language-specific requirements for GSM. These are specific codepoints required by the SMS specifications which in turn are used not only for SMS (GSM 03. 40, 03.41) but also for Unstructured Data (GSM 02.90) and may additionally be used for MMI (GSM 02.30) The specifications for the DCE/DTE interface (GSM 07.05, 07.06) will also use the codes specified herein for the transfer of SMS data to an external terminal.

2 Normative references This ETS incorporates by dated and undated reference, provisions from other publications. These normative references are cited at the appropriate places in the text and the publications are listed hereafter. For dated references, subsequent amendments to or revisions of any of these publications apply to this ETS only when incorporated in it by amendment or revision. For undated references, the latest edition of the publication referred to applies.

[1] GSM 01. 04 (ETR 100) :'European digital cellular telecommunication system (Phase 2) ; Definitions, abbreviations and acronyms".

[2] GSM 02. 30 (ETS 300 511) : "European digital cellular telecommunication system (Phase 2) ; Man-Machine Interface (MMI) of the Mobile Station (MS)".

131 GSM 02.90 (ETS 300 549) :'European digital cellular telecommunication system (Phase 2); Unstructured supplementary services operation - Stage 1".

[4] GSM 03. 40 (ETS 300 536) : "European digital cellular telecommunication system (Phase 2); Technical realization of the Short Message Service (SMS) Point to Point (PP) ".

[5] GSM 03.41 (ETS 300 537) : "European digital cellular telecommunication system (Phase 2); Technical realization of Short Message Service Cell Broadcast (SMSCB)'.

[6] GSM 04.11 (ETS 300 559) :'European digital cellular telecommunication system (Phase 2); Point-to-Point (PP) Short Message Service (SMS) support on mobile radio interface'.

GSM 04.12 (ETS 300 560) :'European digital cellular telecommunication system (Phase 2); Short Message Service Cell Broadcast (SMSCB) support on the mobile radio interface".

[8] GSM 07.05 (ETS 300 585) : "European digital cellular telecommunication system (Phase 2); Use of Data Terminal Equipment-Data Circuit terminating Equipment (DTE-DCE) interface for Short Message Service (SMS) and Cell Broadcast Service (CBS)".

[9] GSM 07.06 (ETS 300 586) : "European digital cellular telecommunication system (Phase 2); Use of the V series Data Terminal Equipment-Data Circuit terminating Equipment (DTE-DCE) interface at the Mobile Station (MS) for Mobile Termination (MT) configuration".

3 Definitions and abbreviations Definitions used in this specification are listed in GSM 01.04.

4 SMS Data Coding Scheme The TP-Data-Coding-Scheme field, defined in GSM 03. 40, indicates the data coding scheme of the TP- U 0 field, and may indicate a message class. The octet is used according to a coding group which is indicated in bits 7.. 4. The octet is then coded as follows :

Coding Group Bits Use of bits 3.. 0 7.. 4 0000 Alphabet indication Unspecified message handling at the MS.

Bits 3.. 0 indicate the alphabet as follows : 0000 Default alphabet 0001.. 1111 Reserved 0001.. 1110 Reserved coding groups 1111 Data coding/message class Bit 3 is reserved, set to O.

Bit 2 Message coding: 0 Default alphabet 1 8-bit data Bit 1 Bit 0 Message Class : 0 0 Class 0 0 1 Class 1 default meaning: ME-specific.

1 0 Class 2 81M-specific message.

1 1 Class 3 default meaning: TE specific (see GSM TS 07.05)

Default alphabet indicates that the TP-UD is coded from the 7-bit alphabet given in subclause 6.2. 1. When this alphabet Is used, the characters of the message are packed in octets as shown in subclause 6. 1. 2.1. 1, and the message can consist of up to 160 characters. The default alphabet shall be supported by all MSs and SCs offering the service.

8-bit data indicates that the TP-UD has user-defined coding, and the message can consist of up to 140 octets.

When a mobile terminated message is class 0 and the MS has the capability of displaying short messages, the MS shall display the message immediately and send an acknowledgement to the SC when the message has successfully reached the MS irrespective of whether there is memory available in the 81M or ME. The message shall not be automatically stored in the SIM or ME.

The ME may make provision through MMI for the user to selectively prevent the message from being displayed immediately.

If the ME is incapable of displaying short messages or if the immediate display of the message has been disabled through MMI then the ME shall treat the short message as though there was no message class, i. e it will ignore bits 0 and 1 in the TP-DCS and normal rules for memory capacity exceeded shall apply.

When a mobile terminated message is Class 1, the MS shall send an acknowledgement to the SC when the message has successfully reached the MS and can be stored. The MS shall normally store the message in the ME by default, if that is possible, but otherwise the message may be stored elsewhere, e. g. in the SIM. The user may be able to override the default meaning and select their own routing.

When a mobile terminated message is Class 2 (SIM-specific), a phase 2 (or later) MS shall ensure that the message has been transferred to the SMS data field in the SIM before sending an acknowledgement to the SC. The MS shall return a'protocol error, unspecified* error message (see GSM TS 04. 11) if the short message cannot be stored in the SIM and there is other short message storage available at the MS. If all the short message storage at the MS is already in use, the MS shall return "memory capacity exceeded".

When a mobile terminated message is Class 3. the MS shall send an acknowledgement to the SC when the message has successfully reached the MS and can be stored, irrespectively of whether the MS supports an SMS interface to a TE, and without waiting for the message to be transferred to the TE. Thus the acknowledgement to the SC of a TE-specific message does not imply that the message has reached the TE. Class 3 messages shall normally be transferred to the TE when the TE requests'TE-specific" messages (see GSM TS 07.05). The user may be able to override the default meaning and select their own routing.

The message class codes may also be used for mobile originated messages, to provide an indication to the destination SME of how the message was handled at the MS.

The MS will not interpret reserved or unsupported values but shall store them as received. The SC may reject messages with a Data Coding Scheme containing a reserved value or one which is not supported.

5 Cell Broadcast Data Coding Scheme The Cell Broadcast Data Coding Scheme indicates the intended handling of the message at the MS. the alphabet/coding, and the language (when applicable). The octet is used according to a coding group which is indicated in bits 7.. 4. The octet is then coded as follows :

Coding Group Bits Use of bits 3.. 0 7.. 4 0000 Language using the default alphabet Unspecified handling at the MS Bits 3.. 0 indicate the language : 0000 German 0001 English 0010 Italian 0011 French 0100 Spanish 0101 Dutch 0110 Swedish 0111 Danish 1000 Portuguese 1001 Finnish 1010 Norwegian 1011 Greek 1100 Turkish 1101.. 1110 Reserved for European languages 1111 language unspecified 0001.. 0100 Reserved for European Languages using the default alphabet, with unspecified handling at the MS.

0101.. 1110 Reserved coding groups

1111 I Data coding I message handling Bit 3 is reserved, set to 0.

Bit 2 Message coding: 0 Default alphabet 1 a-bit data Bit 1 Bit 0 Message Class : 0 0 No message class.

0 1 Class 1 user defined.

1 0 Class 2 user defined.

1 1 Class 3 default meaning: TE-specific (see GSM TS 07.05) These codings may also be used for Unstructured SS Data and MMI/display purposes.

Messages using the default alphabet are coded with the 7-bit alphabet given in subclause 6.2. 1. The message then consists of 93 user characters.

Messages using 8-bit data have user-defined coding, and will be 82 octets in length.

Class 1 and Class 2 messages may be routed by the ME to user-defined destinations, but the user may override any default meaning and select their own routing.

Class 3 messages will normally be selected for transfer to a TE, in cases where a ME supports an SMS/CBS interface to a TE, and the TE requests "TE-specific. cell broadcast messages (see GSM TS 07.05). The user may be able to override the default meaning and select their own routing.

6 Individual parameters 6.1 General principles 6. 1. 1 General notes Except where otherwise indicated, the following shall apply to all alphabet tables : I : The characters marked "1) " are not used but are displayed as a space.

2: The characters of this set, when displayed, should approximate to the appearence of the relevant characters specified in ISO 1073 and the relevant national standards.

3: Control characters: Code Meaning LF Line feed : Any characters following LF which are to be displayed shall be presented as the next line of the message, commencing with the first character position.

CR Carriage return : Any characters following CR which are to be displayed shall be presented as the current line of the message, commencing with the first character position.

SP Space character.

4: The display of characters within a message is achieved by taking each character in turn and placing it in the next available space from left to right and top to bottom.

6.1. 2 Character packing 6.1. 2.1 SMS Point-to-Point Packing 6.1. 2.1. 1 Packing of 7-bit characters If a character number a is noted in the following way:

b7 b6 b5 b4 b3 b2 b1 as ab ac ad ae at ag The packing of the 7-bits characters in octets is done by completing the octets with zeros on the left.

For examples, packing: one character in one octet: bits number:

76543210 0 1a 1b 1c 1d 1e 1f 19 two characters in two octets: bits number:

7 6 5 4 3 2 1 0 2g 1a 1b 1c 1d 1e 1f 1g 0 0 2a 2b 2c 2d 2e 2f three characters in three octets : bits number:

7 6 5 4 3 2 1 0 2g 1a 1b 1c 1d 1e 1f 1g 3f 39 2a 2b 2c 2d 2e 2f 0 0 0 3a 3b 3c 3d 3e seven characters in seven octets: bits number:

7 6 5 4 3 2 1 0 2g 1a 1b 1c 1d 1e 1f 19 3f 3g 2a 2b 2c 2d 2e 2f 4e 4f 4g 3a 3b 3c 3d 3e 5d 5e 5f 59 4a 4b 4c 4d 6c 6d 6e 6f 6g 5a 5b 5c 7b 7c 7d 7e 7f 79 6a 6b 0 0 0 0 0 0 0 7a eight characters in seven octets: bits number:

76543210 2g 1a 1b 1c 1d 1e 1f 19 3f 39 2a 2b 2c 2d 2e 2f 4e 4f 49 3a 3b 3c 3d 3e 5d 5e 5f 5g 4a 4b 4c 4d 6c 6d 6e 6f 6g 5a 5b 5c 7b 7c 7d 7e 7f 7g 6a 6b 8a 8b 8c 8d 8e 8f 89 7a The bit number zero is always transmitted first.

Therefore, in 140 octets, it is possible to pack (140x8)/7=160 characters.

6.1. 2.2 SMS Cell Broadcast Packing 6. 1. 2. 2.1 Packing of 7-bit characters If a character number a is noted in the following way:

b7 b6 b5 b4 b3 b2 b1 aa ab ac ad ae af ag the packing of the 7-bits characters in octets is done as follows

Bit number 7 6 5 4 3 2 1 0 Octet number 1 2g 1a 1b 1c Id 1e 1f 1g 2 3f 3g 2a 2b 2c 2d 2e 2f 3 4e 4f 4g 3a 3b 3c 3d 3e 4 5d 5e 5f 5g 4a 4b 4c 4d 5 6c 6d 6e 6f 6g Sa 5b 5c 6 7b 7c 7d 7e 7f 79 6a 6b 7 8a Ob 8c 8d 8e 8f 8g 7a 8 109 9a 9b 9c 9d 9e 9f 9g 81 93d 93e 93f 93g 92a 92b 92c 92d 82 0 0 0 0 0 93a 93b 93c The bit number zero is always transmitted first.

Therefore, in 82 octets, it is possible to pack (82x8) f7 = 93.7, that is 93 characters. The 5 remaining bits are set to zero as stated above.

6.2 Alphabet tables This section provides tables for all the alphabets to be supported by SMS. The default alphabet is mandatory. Additional alphabets are optional. Irrespective of support of an individual alphabet, an MS shall have the ability to store a short message coded in any alphabet on the SIM.

6.2. 1 Default alphabet Bits per character 7 SMS User Data Length meaning : Number of characters CBS pad character CR Character table :

b7 0 0 0 0 1 1 1 1 b6 0 0 1 1 0 0 1 1 b5 0 1 0 1 0 1 0 1 b4 b3 b2 b1 0 1 2 3 4 5 6 7 0 0 0 0 0 &commat; # SP 0 i P ~ p 0 0 0 1 1 # 1) ! 1 A Q a q 0 0 1 0 2 $ # " 2 B R b r 0 0 1 1 3 ~ # &num; 3 C S c s 0 1 0 0 4 # # 4 D T d t 0 1 0 1 5 # % 5 E U e u 0 1 1 0 6 # & 6 F V f v 0 1 1 1 7 # ' 7 G W g w 1 0 0 0 8 # ( 8 H X h x 1 0 0 1 9 # ) 9 I Y i y 1 0 1 0 10 LF # * : J Z j z 1 0 1 1 11 # 1) + ; K k 1 1 0 0 12 # # , < L l 1 1 0 1 13 CR - = M m 1 1 1 0 14 . > N n 1 1 1 1 15 / ? O o

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. i) 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 RS-232 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" (I) x 1. 047" (h), (56. 64 mm x 96. 42 mm x 26. 60 mm) 1.4. 2 Environmental Characteristics 1) Operating temperature :-30 C to +85 C (intemal temperature) 2) Storage temperature :-40 C to +90 C

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 1 OOOmW 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 10 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

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 sert 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 wel

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. Th GPS 35LP AutolocateTu 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 dateltime 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 wig begin sending valid navigation information over its output channels. These data include : 1) Latitude/tongitude/altitude 2) Velocity 3) Dateltime 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 attitude supplied by the host system (attitude hold mode) 2) 3D exclusively with attitude 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 attitude control.

The GPS 35LP will default to automatic differential mode - -rooking- 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 SATELUTE 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) It 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 TM. This procedure is fully automatic and, under normal circumstances, will require 1.5

Tll 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.

3.2 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.

3. 2. 2 Trunk Lip Mount The trunk lip mount provides a semi-permanent attachment to the trunk lip of most automobiles.

3.2. 3 Suction Cup Mount The suction cup bracket provides a removable mounting surface attached to the inside of a vehicle's windshield.

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.

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.

Red: Vin-Regulated +3.6V to +6V, 150 mA (maximum) in the-LVx versions. Typical operating current is 120 mA. Transients and overvoftages 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 SOOmW 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 OV and Vin in the-LVC version. In the-LVS and-HVS versions a RS-232 compatible output dnver is available. This output normally provides serial data which is formatted per "NMEA 0183, Version 2. 0". Switch able 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 RTCMRecommendedStandards For Differen/ia)/star 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 OV and Vin in the-LVx versions, and OV 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. SV.

Active if greater than 2.7V. Typical switch point is 2. 0V &commat; 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 1 mA in the-HVx. The computer will be reset when power is restored.

Section 4 Software Interface The GPS 35LP interface protocol design is based on the National Marine Electronics Association's NMEA 0183 ASCII interface specification, which is fully defined in ? MME4 0183, Version 2. C" (copies may be obtained from NMEA, P. O. Box 50040, Mobile, AL, 36605, USA) and the Radio Technical Commission for

Maritime Services'' ? ? 7CM Recomnended SXaeyo ?/bf ?/en 9/7 < ra/ Ansy G/ e, ce s/on 2 1, RTCM Special Comm/77ttee N'./C4' (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.

4. 1 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 > . < I2 > . < 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 > 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.

< 2 > Number of current ALM sentence. This field can be null or any number when sending almanac to the sensor board.

< 3 > Satellite PRN number, 01 to 32.

< 4 > GPS week number.

< 5 > SV health, bits 17-24 of each almanac page.

< 6 > Eccentricity < 7 > Almanac reference time.

< 8 > Inclination angle.

< 9 > Rate of right ascension.

< 10 > Root of semi major axis.

< 11 > Omega, argument of perigee.

< 12 > Longitude of ascension node.

< 13 > Mean anomaly < 14 > afo clock parameter < 15 > af1 clock parameter

4. 1. 2 Sensor Initialization Information (PGRMI) The $PGRMI sentence provides information used to initialize the sensor board set position and time used for satellite acquisition. Receipt of this sentence by the board set 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 can also be obtained by sending $PGRMIE to the board.

$PGRMI, < : 1 > , < 2 > , < 3 > , < 4 > , < 5 > , < 6 > , < 7 > *hh < CR > < LF > < 1 > Latitude, ddmm. mmm format (leading zeros must be transmitted) < 2 > Latitude hemisphere, N or S < 3 > Longitude, dddmm. mmm format (leading zeros must be transmitted) < 4 > Longitude hemisphere, E or W < 5 > Current UTC date, ddmmyy format < 6 > Current UTC time, hhmmss format < 7 > Receiver Command, A = Auto Locate, R = Unit Reset 4.1. 3 Sensor Configuration Information (PGRMC) The $PGRMC sentence provides 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. f 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 board.

$PGRMC, < 1 > , < 2 > , < 3 > , < 4 > , < 5 > < 6 > < 7 > < 8 > < 9 > < 10 > < 11 > < 12 > < 13 > < 14 > *hh < CR > < LF > < 1 > Fix mode, A = automatic, 2 = 20 exclusively (host system must supply altitude), 3 = 3D exclusively < : 2 > Altitude aboveJbelow mean sea level,-1500. 0 to 18000.0 meters < 3 > Earth datum index. ff the user datum index (96) Is specified, fields < 4 > through < 8 > must contain valid values. Othetwise, fields < 4 > through < 8 > must be null. Refer to Appendix A for a list of earth datums and the corresponding earth datum index.

< 4 > User earth datum semi-major axis, 6360000. 0 to 6380000. 0 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 conrdinate, -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 Baud rate, 1 = 1200, 2 = 2400, 3 = 4800. 4 = 9600. 5 = 19200, 6 = 300, 7 = 600 < 11 > Velocity filter, 0 = No filter, 1 = Automatic filter, 2-255 = Filter time constant (10 = 10 second filter < 12 > PPS mode. 1 = No PPS, 2 = 1 Hz < 13 > PPS pulse length, 0-48 = (n+1) *20msec. Example n == 4 q 100 msec pulse < 14 > Dead reckoning valid time 1-30 (sec) 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 $PGRMC1 E to the board.

$PGRMC1, < 1 > , < 2 > 'hh < CRxLF > < 1 > NMEA output time 1-900 (sec).

< 2 > Binary Phase Output Data, 1 = Off, 2 = On.

Configuration changes take effect on the next power cycle or an external reset event.

4.1. 5 Output Sentence EnablelDisable (PGRMO) The $PGRMO sentence provides the ability to enable and disable specific output sentences.

The following sentences are enabled at the factory: GPGSA, GPGSV, GPRMC, PGRME, PGRMT and PGRMV $PGRMO, < 1 > , < 2 > *hh < CR > < LF > < 1 > Target sentence description (e. g., PGRMT, GPGSV, etc.) < 2 > 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 no 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.

4.2 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 characters~transmittedpersec 300 30 600 60 1200 120 2400 240 4800 480 9600 960 19200 1920 Sentence maxcharacters GPGGA 81 GPGSA 66 GPGSV 210 GPRMC 73 GPVTG 40 PGRME 35 PGRMT 50 PGRMV 32 PGRMF 82 LCGLL 41 LCVTG 37 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 on-board 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 Wationallnstitule of Standards and Technology Special Publication 432 ese < //aa' (for sate 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 Oh Om Os 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 Time 311289 235959 311289 235960 010190 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 > , < 1 0 > . < 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) $GPGGA, < 1 > , < 2 > . < 3 > , < 4 > , < 5 > , < 6 > , < 7 > , < 8 > , < 9 > , M, < 10 > . M, < 11 > , < 12 > *hh < CR > < LF > < 1 > UTC time of position fix, hhmmss format < 2 > Latitude, ddmm. mmmm format (leading zeros will be transmitted) < 3 > Latitude hemisphere, N or S < 4 > Longitude, dddmm. mmmm format (leading zeros will be transmitted) < 5 > Longitude hemisphere, E or W

< 6 > GPS quality indication, 0 = fix not available, 1 = Non-differential GPS fix available, 2 = Differential GPS (DGPS) fix available < 7 > Number of satellites in use, 00 to 12 (leading zeros will be transmitted) < 8 > Horizontal dilution of precision, 0.5 to 99.9 < 9 > Antenna height abovelbelow mean sea level,-9999. 9 to 99999.9 meters < 1 < Geoidal height, -999. 9 to 9999.9 meters < 11 > Differential GPS (RTCM SC-104) data age, number of seconds since last valid RTCM transmission (null if non-DGPS) < 12 > Differential Reference Station ID, 0000 to 1023 (leading zeros transmitted, null if non-DGPS) 4.2. 5 GPS DOP and Active Satellites (GSA)

$GPGSA, < 1 > , < 2 > , < 3 > , < 3 > , < 3 > , < 3 > , < 3 > , < 3 > , < 3 > . < 3 > , < 3 > , < 3 > , < 3 > , < 3 > , < 4 > , < 5 > , < 6 > *hh < CR > < LF > < 1 > Mode, M = manual, A = automatic < 2 > Fix type, 1 = not available, 2 = 2D, 3 = 3D < 3 > PRN number, 01 to 32. of satellite used in solution, up to 12 transmitted (leading zeros will be transmitted) < 4 > Position dilution of precision, 0.5 to 99.9 < 5 > Horizontal dilution of precision, 0.5 to 99.9 < 6 > Vertical dilution of precision, 0.5 to 99.9 4. 2. 6 GPS Satellites in View (GSV) $GPGSV, < 1 > , < 2 > . < 3 > , < 4 > . < 5 > , < 6 > . < 7 > .... < 4 > . < 5 > , < 6 > , < 7 > *hh < CR > < LF > < 1 > Total number of GSV sentences to be transmitted < 2 > Number of current GSV sentence < 3 > Total number of satellites in view, 00 to 12 (leading zeros will be transmitted) < 4 > Satellite PRN number. 01 to 32 (leading zeros will be transmitted) < 5 > Satellite elevation, 00 to 90 degrees (leading zeros will be transmitted) < 6 > Satellite azimuth, 000 to 359 degrees, true (leading zeros will be transmitted) < 7 > 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 sentences. These fields will be null if unused.

4.2. 7 Recommended Minimum Specific GPSfTRANSIT Data (RMC) $GPRMC, < 1 > , < 2 > , < 3 > . < 4 > , < 5 > . < 6 > , < 7 > . < 8 > . < 9 > , < 10 > , < 11 > 'hh < CR > < LF > < 1 > UTC time of position fix, hhmmss format < 2 > Status, A = Valid position, V = NAV receiver warning < 3 > Latitude, ddmm. mmmm format (leading zeros will be transmitted) < 4 > Latitude hemisphere, N or S < 5 > Longitude, dddmm. mmmm format (leading zeros will be transmitted) < 6 > Longitude hemisphere, E or W < 7 > Speed over ground, 0.0 to 1851.8 knots < 8 > Course over ground, 000.0 to 359.9 degrees, true (leading zeros will be transmitted) < 9 > UTC date of position fix, ddmmyy format < 10 > Magnetic variation, 000.0 to 180.0 degrees (leading zeros will be transmitted) < 11 > Magnetic variation direction, E or W (westerly variation adds to true course)

4. 2. 8 Track Made Good and Ground Speed with GPS Talker ID (VTG) The GPVTG sentence reports track and velocity information with a checksum:

$GPVTG, < 1 > , T, < 2 > , M, < 3 > , N, < 4 > , K*hh < CR > < LF > < 1 > True course over ground, 000 to 359 degrees (leading zeros will be transmitted) < 2 > Magnetic course over ground, 000 to 359 degrees (leading zeros will be transmitted) < 3 > Speed over ground, 00.0 to 999.9 knots (leading zeros will be transmitted) < 4 > Speed over ground, 00.0 to 1851.8 kilometers per hour (leading zeros will be transmitted) 4.2. 9 Geographic Position with LORAN Talker ID (LCGLL) The LCGLL sentence reports position information.

$LCGLL, < 1 > , < 2 > , < 3 > , < 4 > , < 5 > . < CR > < LF > < 1 > Latitude, ddmm. mmmm format (leading zeros will be transmitted) < 2 > Latitude hemisphere, N or S < 3 > Longitude, dddmm. mmmm format (leading zeros will be transmitted) < 4 > Longitude hemisphere, E or W < 5 > UTC time of position fix, hhmmss format 4. 2. 10 Track Made Good and Ground Speed with LORAN Talker ID (LCVTG) The LCVTG sentence reports track and velocity information.

$LCVTG, < 1 > , T, < 2 > , M, < 3 > , N, < 4 > , K < CR > < LF > < 1 > True course over ground, 000 to 359 degrees (leading zeros will be transmitted) < 2 > Magnetic course over ground, 000 to 359 degrees (leading zeros will be transmitted) < 3 > Speed over ground, 00.0 to 999.9 knots (leading zeros will be transmitted) < 4 > Speed over ground, 00.0 to 1851.8 kilometers per hour (leading zeros will be transmitted)

4. 2. 11 Estimated Error Information (PGRME) The GARMIN Proprietary sentence $PGRME reports estimated position error information.

$PGRME. < l > , M, < 2 > , M, < 3 > , M*hh < CR > < LF > < 1 > Estimated horizontal position error (HPE), 0.0 to 999.9 meters < 2 > Estimated vertical position error (VPE), 0.0 to 999.9 meters < 3 > Estimated position error (EPE), 0.0 to 999.9 meters

4.2. 12 GPS Fix Data Sentence (PGRMF) The sentence $PGRME is GARMtN Proprietary format.

$PGRMF, < 1 > , < 2 > , < 3 > , < 4 > . < 5 > , < 6 > , < 7 > . < 8 > , < 9 > , < 1 0 > , < 11 > , < 12 > . < 13 > . < 14 > , < 15 > *hh < CR > < LF > < 1 > GPS week number (0-1023) < 2 > GPS seconds (0-604799) < 3 > UTC date of position fix, ddmmyy format < 4 > UTC time of position fix, hhmmss format < 5 > GPS leap second count < 6 > Latitude, ddmm. mmmm format (leading zeros will be transmitted) < 7 > Latitude hemisphere, N or S < 8 > Longitude, dddmm. mmmm format (leading zeros will be transmitted) < 9 > Longitude hemisphere, E or W < 10 > Mode, M = manual, A = automatic < 11 > Fixtype, 0=nofix, 1=2DftX, 2=3Dfix < 12 > Speed over ground, 0 to 1851 kilometers/hour < 13 > Course over ground, 0 to 359 degrees, true < 14 > Position dilution of precision, 0 to 9 (rounded to nearest integer value) < 15 > Time dilution of precision, 0 to 9 (rounded to nearest integer value) 4.2. 13 Sensor Status Information (PGRMT) The GARMIN Proprietary sentence $PGRMT gives information concerning the status of the sensor board.

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 > Product, model and software version (variable length field, e. g., "GPS 25LP VER 1.10") < 2 > ROM checksum test, P = pass, F = fail < 3 > Receiver failure discrete, P = pass, F = fail < 4 > Stored data lost, R = retained, L = lost < 5 > Real time clock lost, R = retained, L = lost < 6 > Oscillator drift discrete, P = pass, F = excessive drift detected < 7 > Data collection discrete, C = collecting, null if not collecting < 8 > Board temperature in degrees C < 9 > Board configuration data, R = retained, L = lost 4.2. 14 3D velocity Information (PGRMV)

The GARMIN Proprietary sentence $PGRMV reports three-dimensional velocity information.

$PGRMV, < 1 > , < 2 > , < 3 > 'hh < CRxLF > < 1 > True east velocity. -514. 4 to 514. 4 m/second < 2 > True north velocity,-514. 4 to 514. 4 m/second < 3 > Up velocity.-999. 9 to 9999.9 m/second 4.3 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)

4.4 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 > .

4.5 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 104-68 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) : 0 ADINDAN-Ethiopia, Mali, Senegal, Sudan 1 AFGOOYE - Somalia 2 AIN EL ABD 1970-Bahrain Island, Saudi Arabia 3 ANNA 1 ASTRO 1965 - Cocos Island 4 ARC 1950-Botswana, Lesotho, Malawi, Swaziland, Zaire, Zambia, Zimbabwe 5 ARC 1960-Kenya, Tanzania 6 ASCENSION ISLAND 1958-Ascension Island 7 ASTRO BEACON"E"-iwo Jima Island 8 AUSTRALIAN GEODETIC 1966 - Australia, Tasmania Island 9 AUSTRALIAN GEODETIC 1984-Australia, Tasmania Island 10 ASTRO DOS 71/4 - Sl Helena Island 11 ASTRONOMIC STATION 1952-Marcus Island 12 ASTRO B4 SOROL ATOLL - Tem Island 13 BELLEVUE (IGN)-Efate and Erromango Islands 14 BERMUDA 1957 - Bermuda Islands 15 BOGOTA OBSERVATORY-Colombia 16 CAMPO INCHAUSPE-Argentina 17 CANTON ASTRO 1966-Phoenix Islands 18 CAPE CANAVERAL-Florida. Bahama Islands 19 CAPE-South Africa 20 CARTHAGE-Tunisia 21 CHATHAM 1971-Chatham Island (New Zealand) 22 CHUA ASTRO-Paraguay 23 CORREGO ALEGRE-Brazil 24 DJAKARTA (BATAVIA)-Sumatra Island (Indonesia) 25 DOS 1968 - Gizo Island (New Georgia Islands) 26 EASTER ISLAND 1967 - Easter Island 27 EUROPEAN 1950 - Austria, Belgium, Denmark, Finland, France, Germany, Gibraltar, Greece, Italy, Luxembourg, Netherlands, Norway, Portugal. Spain, Sweden, Switzerland 28 EUROPEAN 1979-Austria, Finland, Netherlands, Norway, Spain, Sweden, Switzerland 29 FINLAND HAYFORD 1910-Finland 30 GANDAJIKA BASE-Republic of Maldives 31 GEODETIC DATUM 1949-New Zealand 32 ORDNANCE SURVEY OF GREAT BRITAIN 1936-England, Isle of Man, Scotland, Shetland Islands, Wales 33 GUAM 1963-Guam Island 34 GUX 1 ASTRO-Guadalcanal Island 35 HJORSEY 1955-Iceland 36 HONG KONG 1963-Hong Kong 37 INDIAN-Bangladesh, India, Nepal 38 INDIAN - Thailand, Vietnam 39 IRELAND 1965-Ireland

40 ISTS 073 ASTRO 1969-Diego Garcia 41 JOHNSTON ISLAND 1961 - Johnston Island 42 KANDAWALA-Sri Lanka 43 KERGUELEN ISLAND-Kerguelen Island

44 KERT AU 1948 - West Malaysia, Singapore 45 L. C. 5 ASTRO-Cayman Brae (stand 46 LIBERIA 1964-Liberia 47 LUZON-Mindanao Island 48 LUZON-Phillippines (excluding Mindanao Island) 49 MAHE 1971 - Mahe Island 50 MARCO ASTRO-Salvage Islands 51 MASSAWA-Eritrea (Ethiopia) 52 MERCHICH-Morocco 53 MIDWAY ASTRO 1961 - Midway Island 54 MINNA-Nigeria 55 NORTH AMERICAN 1927-Alaska 56 NORTH AMERICAN 1927-Bahamas (excluding San Salvador Island) 57 NORTH AMERICAN 1927 - Central America (Belize, Costa Rica, El Salvador, Guatemala, Honduras, Nicaragua) 58 NORTH AMERICAN 1927-Canal Zone 59 NORTH AMERICAN 1927-Canada (including Newfoundland Island) 60 NORTH AMERICAN 1927-Caribbean (Barbados, Caicos Islands, Cuba, Dominican Republic, Grand Cayman, Jamaica, Leeward Islands, Turks Islands) 61 NORTH AMERICAN 1927 - Mean Value (CONUS) 62 NORTH AMERICAN 1927-Cuba 63 NORTH AMERICAN 1927-Greenland (Hayes Peninsula) 64 NORTH AMERICAN 1927-Mexico 65 NORTH AMERICAN 1927-San Salvador Island 66 NORTH AMERICAN 1983 - Alaska, Canada, Central America, CONUS, Mexico 67 NAPARIMA, BWI-Trinidad and Tobago 68 NAHRWAN-Masirah Island (Oman) 69 NAHRWAN-Saudi Arabia 70 NAHRWAN-United Arab Emirates 71 OBSERVATORIO 1966-Corvo and Flores Islands (Azores) 72 OLD EGYPTIAN-Egypt 73 OLD HAWAIIAN-Mean Value 74 OMAN-Oman 75 PICO DE LAS NIEVES-Canary Islands 76 PITCAIRN ASTRO 1967 - Pitcairn Island 77 PUERTO RICO-Puerto Rico, Virgin Islands 78 QATAR NATIONAL-Qatar 79 OORNOQ - South Greenland 80 REUNION-Mascarene Island 81 ROME 1940-Sardinia Island 82 RT 90-Sweden 83 PROVISIONAL SOUTH AMERICAN 1956-Bolivia, Chile, Colombia, Ecuador, Guyana, Peru, Venezuela 84 SOUTH AMERICAN 1969-Argentina, Bolivia, Brazil, Chile, Colombia, Ecuador, Guyana, Paraguay, Peru, Venezuela, Trinidad and Tobago 85 SOUTH ASIA-Singapore 86 PROVISIONAL SOUTH CHILEAN 1963. South Chile 87 SANTO (DOS)-Espirito Santo Island

88 SAO BRAZ-Sao Miguel, Santa Maria Islands (Azores) 89 SAPPER HILL 1943 - East Falkland Island 90 SCHWARZECK-Namibia 91 SOUTHEAST BASE-Porto Santo and Madeira Islands 92 SOUTHWEST BASE-Faial, Graciosa, Pico, Sao Jorge, and Terceira Islands (Azores) 93 TIMBALAI 1948-Brunei and East Malaysia (Sarawak and Sabah) 94 TOKYO-Japan, Korea, Okinawa 95 TRISTAN ASTRO 1968-Tristan da Cunha 96 User defined earth datum 97 VITILEVU 1916 - Viti Levu Island (Fiji Islands) 98 WAKE-ENIWETOK 1960-Marshall Islands 99 WORLD GEODETIC SYSTEM 1972 100 WORLD GEODETIC SYSTEM 1984 101 ZANDERIJ-Surinam

102 CH-1903 - Switzerland 103 Hu-Tzu-Shan 104 Indonesia 74 105 Austria 106 Potsdam 107 Taiwan (modified Hu-Tzu-Shan)

Appendix B GPS 35LP Evaluation Kits GPS 35LP evaluation materials kit (part number 010-10186-00) is available from Garmin Intemational.

This kit includes two DB-9 connectors with solder pots, various mounting brackets, hookup wire, technical specification, and software to monitor the GPS 35LP outputs and configure the receiver.

To install the evaluation and configuration software run the program, setup, by using the FILE-RUN command in Windows.

NMEAVWR. EXE The NMEAVWR. EXE program in the GARMIN program group can accept NMEA data from either the com1 or com2 PC serial port at 1200,2400, 4800,9600 or 19200 baud. The default settings are com1 at 4800 baud. NMEAVWR receives NMEA sentences and displays sentence information in a formatted display on the screen.

The top portion of the screen displays the 5 character identifier of sentences received, the age in seconds since the last transmission, and a count of the number of times the sentence has been received. The middle portion of the screen displays the most recently received data in the sentence with the selected NMEA identifier (highlighted in the top portion of the screen using the arrow keys).

The lower portion contains a formatted presentation of the currently selected sentence. In addition to

receiving data the program will also upload NMEA sentences to the sensor board. The ALT-U key sequence will upload the file NMEA. TXT in the current directory to the unit. Received data can also be logged to a file. NMEAVWR can be invoked from a DOS prompt with the following optional parameters : < path > nmeavwr [/b : < baud > ] [ < port > ] [logfile. txtJ where: [] brackets indicate optional parameters < path > DOS path to nmeavwr. exe if not in current directory < baud > baud rate < port > PC communications port togfi) e. txt ASO) tog fiie of all received sentences Example :

c : \garmin > nmeavwr/b : 9600 com2 logfile. txt If no options are used. the defaults are 4800 baud, com1, and no data logging.

GPSCFG. EXE The configuration program GPSCFG. EXE will configure the sensor boards based on user selected parameters. Some program features include the ability to download sensor board configuration, maintain different configurations in files, and perform sensor board configurations quickly with the use of one function key. Online program help is available.

GPS25PM. EXE The Garmin Phase Monitor Program, GPS25PM. EXE, provides the following functions: - Display and log phase data output from TXD2 - Upload almanac, position, and time information via RXD2 - Download almanc and ephemeris information upon command GPS25PM. EXE can be invoked from a DOS prompt: < path > gps25pm. exe [/com < x > j Vb : < yyyy > j Where < > denotes user supplied information [) denotes optional parameters x is com port number (1 or 2, default is 1) yyyy is baud rate (1200, 2400, 4800, or 9600, default is 9600) See Appendix C for detailed description and operation of the GPS25PM. EXE program.

Appendix C Phase Output Data Binary Format Two records are transmitted once per second by the GPS 35LP. One record contains primarily post- process information such as position and velocity information. The second record contains receiver measurement information. The records are sent at a default baud rate of 9600 baud, 8 bits, no parity.

Records begin with a delimiter byte (10 hex). The second byte identifies the record type (28 hex for a position record, 29 hex for a receiver measurement). The third byte indicates the size of the data. The fourth byte is the first byte of data. The data is then followed by a chksum byte, a delimiter byte (10 hex), and an end-of-transmission character (03 hex).

Note-If RTCM-104 differential data is sent to the GPS 35LP the board will reset the Phase Output Data baud rate to the same baud rate used for RTCM-104 data. If the differential inputs are used on the GPS 35LP then the RTCM-104 data must be sent to the GPS 35LP at 9600 baud (preferred) or 4800 baud.

RTCM-104, baud rates less than 4800 baud are not supported by the GPS 35LP since it would limit bus bandwidth past the point where a once per second phase output data rate could be maintained.

Position Record - Ox10 (die is first byte) Ox28 (position record identifier) - 0x36 (size of data) - cpopvttype (see description below) - one byte chksum (the addition of bytes between the deli miters should equal 0) oxio (dle) - 0x03 (etx is last byte) typedef struct { float alt ; float epe; float eph ; float epv; int fix ; double gpstow ; double lat ; double Ion ; float lon~vel ; float latvel ; float art-vol ;

} cpopvttype ; alt ellipsoid altitude (mt) epe est pos error (mt) eph pos err, horizontal (mt) epv pos err, vertical (mt) fix 0 = no fix; 1 = no fix; 2 = 2D ; 3 = 3D ; 4 = 20 differential ; 5 = 3D differential ; 6 and greater-not defined

gps~tow gps time of week (sec) lat Latitude (rad) Ion Longitude (rad) lon~vel Longitude vetocity (mt/sec) latvel Latitude velocity (mVsec) attvel Altitude velocity (msec) Receiver Measurement Record - oxio (die is first byte) -0x29 (receiver record identifier) - OxE2 (size of data) -cpo~rcv-type (see below) - one byte chksum (the addition of bytes between the delimiters should equal 0) - Ox10 (die) -0x03 (etx)

typedef struct f unsigned long cycles ; double pr; unsigned int phase; char slpdtct ; unsigned char snr~dbhz ; char svid; char valid ; ) cpo~rcv~sv~type ;

typedef struct { double rcvrtow ; int rcvr~wn ; cpo~rcv~sv~type sv {12] ; } cporcvtype ; rcvrtow Receiver time of week (sec) rcvr~wn Receiver week number cycles Number of accumulated cycles pr pseudo range (mt) phase to convert to (0-359. 999) multiply by 360.0 and divide by 2048.0 slp-dtct 0 = no cycle slip detected; non 0 = cycle slip detected snr-dbhz Signal strength svid Satellite number (0-31) Note-add 1 to offset to current svid numbers valid 0 = information not valid ; non 0 = information valid

die and etx bytes : Software written to receive the two records should filter die and etx bytes as described below : typedef enum { dat, die, etx } rxstatetype ; char In~que[2561 ; int inqueptr = 0 ; rxstatotype rxstate = dat ; void addtoque (char data) { &num;define dieebyte Ox10 &num;define etx~byte Ox03 if (rx~state = dat) ( if (data = die-byte) ( rxstate = die ; ) else ( inque [inqueptr-+] = data ; ) ) else if (rx~state = die) { if (data= etxbyte) { rx~state = etx ; } else ( rx~state = dat ; inque [inqueptr-)-] = data ; ) } else if (rxstate = etx) { if (data = die~byte) { rx~state = die ; } } if (inqueptr > 255) { in~que-ptr = 0 ; } }

GARMIN Phase Monitor Program-gps25pm. exe Command Line Arguments default : Icom1 - selects which PC serial port to use for communication-com1, com2 (com1 default).

1b : 9600-selects the baud rate - 1200, 2400, 4800, or 9600 (9600 default) 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. Attitude (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.

The bottom section contains program messages. Upload and download status messages will appear here as well as any program error messages.

Commands : D-Download Almanac : The GPS25 sensor will be sent a command to download almanac information. GPS25PM. EXE will create the file ALMANAC. DAT and locate it the current working directory. If an ALMANAC. DAT exists in the current directory it will be over-written.

U - Upload Almanac : The ALMANAC. DAT file located in the current working directory will be read, converted to GPS25 sensor binary format, and sent to the GPS25 sensor. This command will over-write any almanac information already in the GPS25 sensor.

E-Download Ephemeris: The GPS25 sensor will be sent a command to download ephemeris information. GPS25PM. EXE will create the file EPHEMERS. DAT and locate it in the current working directory. If an EPHEMERIS. DAT exists in the current directory it will be over-written.

P-Position and Time Upload : The program will prompt the user for the local time offset from UTC time. This offset is then used to determine UTC time from the PC's real time clock. The UTC time is then uploaded to the GPS25 sensor.

If an error occurs in the upload process a'COMM ERROR'will be enunciated on the screen. After the UTC time has been uploaded the user is prompted for Latitude and Longitude for position uploading. An integer Latitude and integer Longitude should be entered on the same line separated by a space. If the board has not yet obtained a position fix it will restart its startup sequence based on the new position and time information.

R-Record Data The program will prompt the user for a data file name. GPS25XL. DAT is the default. Once the file name is obtained all information displayed in the top two sections of the screen will be formatted and written to the data file. The format of this data file is described in the File Formats section. If the R option is selected again, the current file will be saved and closed and a new file will be opened. Data files will be over-written if same names are used.

File Formats ALMANAC. DAT Example almanac entry: **** Week 794 almanac for PRN-01 10 : 01 Health : 000 Eccentricity: 3. 414630890E-003 Time of Applicability (s): 380928.0000 Orbital Inclination (rad): 9. 549833536E-001 Rate of Right Ascen (r/s) : -7.771752131E-009 SORT (A) (mAl/2) : 5153.589843 Right Aseen at TOA (rad): 8.032501489E-002 Argument of Perigee (rad) : -1. 308424592E+OOO Mean Anom (rad) : 2. 045822620E+OOO AfO (s) : 9. 536743164E-007 Af1 (s/s) : 8. 367351256E-011 week : 794 Almanac information for satellites with a bad health status will not be included in this file when downloaded from the GPS25 sensor and should not be included when uploading to the GPS25 sensor.

EPHEMERS. DAT Example ephemeris entry : *'"Week 794. Ephemeris for PRN-18 ********** Ref Time of Clk Parms (s): 233504.000000 Ref Time of Eph Parms (s): 233504.000000 Clk Cor, Group Dly (s) :-8. 280389E-006 Clk Correction af1 (sots) :-3. 410605E-013 Clk Correction af2 (s/s/s) : O. OOOOOOE+OOO User Range Accuracy (m): 33. 299999 Eccentricity (-): 5. 913425E-003 SQRT (A) (m-1/2) : 5. 153628E+003 Mean Motion Cor (r/s) : 4. 710911 E-009 Mean Anomaly (r): 6.033204E-001 Argument of Perigee (r): 1. 418009E+000 Right Ascension (r): 3.520111 E-002 Inclination Angle (r): 9.434418E-001 Rate of Right Asc (r/s) :-8. 210699E-009 Rate of Inc Angle (r/s): 4. 503759E-010 Lat Cor, Sine (r): 1. 212582E-005 Lat Cor, Cosine (r) : 2.004206E-006 Inc Cor, Sine (r) :-1. 490116E-008 Inc Cor, Cosine (r) :-9. 872019E-008 Radius Cor, Sine (m): 38.375000 Radius Cor, Cosine (m) : 132. 937500 Issue of Data: 184

Ephemeris Record -0x10 (dle is first byte) - Ox2A (ephemeris record identifier) - Ox74 (size of data) - ephtype (see description below) - one byte chksum (the addition of bytes between the delimiters should equal 0) - oxio (die) -Ox03 (etx) typedef struct/* ephemeris record */ { char svid ; r Satellite number (0 - 31) */ int wn ; r week number (weeks) */ float toe ; /* reference time of clock parameters (s) float toe ; /* reference time of ephemeris parameters (s) */ float afO ; r clock correction coefcnt - group delay (s) */ float af1 ; r clock correction coefficient (s/s) */ float af2 ; r clock correction coefficient (sis) float ura ; r user range accuracy (m) */ double e ; r eccentricity (-) V double sqrta ; r square root of semi-major axis (a) (m""1I2)'"I double dn ; /* mean motion correction (r/s) double mO ; r mean anomaly at reference time (r) */ double w; /* argument of perigee (r) */ double omgO ; /* right asscension (r) double iO ; r inclination angle at reference time (r) */ float odot ; /* rate of right ascension (r/s) */ float idot ; r rate of inclination angle (r/s) */ float cus ; r argument of latitude correction, sine (r) */ float cue ; r argument of latitude correction, cosine (r) */ float cis ; r inclination correction, sine (r0 */ float cic ; r inclination correction, cosine (r) */ float crs ; r radius correction, sine (m) */ float crc ; r radius correction, cosine (m) */ byte iod ; r issue of data */

} ephtype ; To initiate an ephemeris download for all tracked satellites send the following bytes in sequence : Os10, OxOD, Ox04, Ox02, OxOC, OxO, OxO, OxE1, Ox10, Ox03 GPS25PM. DAT Example data file entry:

TIM dmeo{week weeknumber RCV svid snr (T) rack/ (C) ycle~slip phase pseudorange cycles PVT time lat Ion ait latvel lon~vel altvel epe eph epv TIM 235537. 99855650 794 RCV 18 50 T 120.2 19964528.44 2068193 RCV 29 50 T 133.2 20364313. 25 1950557 RCV 28 45 T 176.5 21135153. 13 2069992 RCV 19 47 T 145.2 21190271.83 2182643 RCV 31 45 T 75.8 21240354.20 2216421 RCV 22 42 T 195.1 22849183. 41 1855826 RCV 27 36 T 155.2 24234175. 55 2230462 RCV 14 39 T 202.3 25147694.34 1845263 PVT 235537.99999842 38.9499588 94.7463684 211. 7 -0. 19 -0. 31 0.13 28 16 23 TIM 235538.99853500 794 RCV 18 50 T 38.8 19958107.10 2101947 RCV 29 50 T 132.4 20358247.54 1982431 RCV 28 45 T 189.5 21128713.01 2103829 RCV 19 47 T 284.6 21183470. 16 2218374 RCV 31 45 T 19.0 21233441.89 2252746 RCV 22 42 T 263.0 22843381. 08 1886300 RCV 27 36 T 311.7 24227194. 88 2267146 RCV 14 39 T 308.3 25141899.86 1875708 PVT 235538. 99999827 38.9499550 94.7463684 212. 6-0. 19-0. 30 0.14 28 16 23 TIM 235539.99851349 794 RCV 18 50 T 76.6 19951681.26 2135704 RCV 29 50 T 284. 4 20352180.11 2014308 RCV 28 45 T 320.8 21122272.68 2137669 RCV 19 47 T 8.3 21176671.33 2254110 RCV 31 45 T 170.2 21226528. 82 2289074 RCV 22 42 T 315.9 22837584. 50 1916778 RCV 27 36 T 132.4 24220207.85 2303835 RCV 14 39 T 127.4 25136106.23 1906158 PVT 235539.99999812 38.9499512 94.7463684 213. 5-0. 19-0. 30 0.13 28 16 23

TIM 235540. 99849199 794 RCV 18 50 T 174.9 19945258.21 2169465 RCV 29 50 T 177.7 20346113.87 2046190 RCV 28 45 T 159.6 21115834. 07 2171514 RCV 19 47 T 324.7 21169868.61 2289849 RCV 31 45 T 111.8 21219615.05 2325407 RCV 22 42 T 261.7 22831782.87 1947261 RCV 27 36 T 259.1 24213226.41 2340528 RCV 14 39 T 318.7 25130310.86 1936612 PVT 235540.99999797 38.9499474 94.7463760 214. 4 -0. 19 -0. 30 0. 14 28 16 23 TIM 235541. 99847244 794 RCV 18 50 T 325.5 19938831.69 2203229 RCV 29 50 T 152.1 20340045. 44 2078075 RCV 28 45 T 52.4 21109392. 21 2205362 RCV 19 47 T 125.3 21163068.15 2325593 RCV 31 45 T 159.4 21212700.30 2361743 RCV 22 43 T 117.1 22825981.54 1977748 RCV 27 36 T 352.1 24206248.88 2377225 RCV 14 39 T 141.3 25124515.72 1967071 PVT 235541.99999977 38.9499474 94.7463760 215. 4 -0. 19 -0. 30 0.13 28 16 23

Claims

1. A locating system comprising: a mobile transmitter/receiver ; a global positioning receiver coupled to the mobile transmitter/receiver and which can generate positional data defining its position by obtaining data from one or more relevant global positioning transmitters selected from an array of global positioning transmitters, a remote central computer which can communicate with the mobile transmitter/receiver and which when actuated can, in response to the general location of the mobile transmitter/receiver, supply the global positioning receiver through the mobile transmitter/receiver with assistance to select the relevant one or more global positioning transmitters from said array of global positioning transmitters, said global positioning receiver, when actuated, being thereafter able to transmit said positional data to the central computer via said mobile transmitter/receiver.

2. A system according to Claim 1, wherein said general location of the mobile transmitter/receiver to which the central computer responds is that location established on the last occasion that the mobile transmitter/receiver was used.

3. A system according to Claim 1, wherein the said general location of the mobile transmitter/receiver used by the central computer is established in real time.

4. System according to any one of Claims 1 to 3, wherein the mobile transmitter/ receiver comprises a mobile telephone and said remote central computer is coupled to the mobile telephone through a telephone network.

5. A system according to Claim 4, including actuation means located with said global positioning receiver and said mobile transmitter receiving and operable when actuated to actuate the global positioning transmitter and through said mobile transmitter/receiver to actuate said central computer.

6. A system according to Claim 5, wherein the actuating means stores the telephone number through which the central computer can be accessed.

7. A system according to any one of Claims 4 to 6, wherein said positional data is delivered to the central computer using a short message service channel.

8. A system according to any one of Claims 4 to 7, wherein the central computer stores the telephone number of the mobile telephone calling it.

9. A system according to any preceding claim, including means located with the mobile transmitter receiver and the global positioning receiver for indicating that the global positioning receiver is calculating updated positional information.

10. A system according to any preceding claim, including means located with the mobile transmitter/receiver for indicating an error in the transmission of the positional data to the central computer.

11. A locating system substantially as hereinbefore described, with reference to the accompanying drawings.