Motorola M12 Oncore User`s guide

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Chapter 3 – Receiver Description

3.0 RECEIVER DESCRIPTION

CHAPTER SUMMARY

Refer to this chapter for the following:

• A simplified functional description of the operation of the Oncore receiver

• Antenna power and gain requirements

• Physical size and electrical connections of the Oncore receiver

• Oncore receiver technical characteristics and operating features

• Installation precautions and considerations

• Oncore receiver mounting guidelines

• Interface protocol description

• Operational modes of the Oncore receiver

• Additional customizing capabilities and operation

Motorola GPS Products - Oncore User’s Guide

Revision 5.0 08/30/02

3.1

Chapter 3 – Receiver Description

DETAILED TABLE OF CONTENTS

Overview ...................................................................................................................................3.4

Antenna Sense Circuit............................................................................................................3.6

Antenna Feed Current............................................................................................................3.6

Active Antenna Configuration ...............................................................................................3.8

M12+ and M12+ Timer Oncore Receiver Electrical Connections ...................................3.9

Oncore Operation Voltage And Current Ranges ................................................3.9

M12+ Oncore Receiver Printed Circuit Board ..................................................................3.10

M12+ Oncore Receiver Technical Characteristics..........................................................3.11

M12+ Timer Oncore Receiver Technical Characteristics ..............................................3.12

GT+, UT+, SL Oncore Receiver Electrical Connections ..................................................3.13

Oncore Operation Voltage And Current Ranges ..............................................3.13

GT+, UT+, SL Oncore Receiver Printed Circuit Board .....................................................3.14

GT+ Oncore Receiver Technical Characteristics ............................................................3.15

UT+ Oncore Receiver Technical Characteristics ............................................................3.16

SL Oncore Receiver Technical Characteristics ...............................................................3.17

1PPS Signal Definition ..........................................................................................................3.18

RF Jamming Immunity (UT Model Only).............................................................................3.18

Adaptive Tracking Loops .....................................................................................3.19

Automatic Site Survey (UT Model Only) ............................................................................3.20

100PPS Output (UT Model Only)..........................................................................................3.21

Time Raim Algorithm Description (M12 Timing and UT Models Only)..........................3.22

Receiver Module Installation ..............................................................................................3.24

Installation Precautions And Considerations ...................................................................3.24

Electrostatic Precautions ....................................................................................3.24

Electromagnetic Considerations ........................................................................3.24

RF Shielding............................................................................................................3.25

Real-Time Clock (RTC) ..........................................................................................3.25

Thermal Considerations .......................................................................................3.25

Grounding Considerations ...................................................................................3.25

Oncore Receiver Mounting Instructions (GT+/UT+ Only)...............................................3.26

Mounting Hardware Design Guidelines ............................................................3.26

Design and Process Validation Test Information ............................................3.28

Sturdiness and Reliability of Metal Standoffs ..................................................3.29

Design Worksheets...............................................................................................3.29

Mean Time Between Failure (MTBF) .................................................................................3.31

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Chapter 3 – Receiver Description

System Integration ................................................................................................................3.32

Interface Protocol .................................................................................................................3.32

TTL Output...............................................................................................................................3.33

Motorola Binary Format .......................................................................................3.34

NMEA Support .......................................................................................................3.37

RTCM Differential GPS Support ..........................................................................3.38

EXCLUSIVE-OR Checksum Creation...................................................................................3.39

Millisecond To Degree Conversion ....................................................................................3.40

Input/Output Processing Time.............................................................................................3.41

DATA Latency ........................................................................................................................3.42

Position DATA Latency.........................................................................................3.44

Velocity DATA Latency.........................................................................................3.44

Time DATA Latency ..............................................................................................3.44

One Pulse Per Second (1PPS) Timing................................................................................3.44

Measurement Epoch Timing ...............................................................................3.44

Output Data Timing Relative To Measurement Epoch....................................3.45

1PPS Cable Delay and 1PPS OfFset (M12 Timing and UT Model Only)........3.46

Operational Considerations .................................................................................................3.47

First Time On ..........................................................................................................3.47

Initialization ............................................................................................................3.48

Shut Down ..............................................................................................................3.48

Keep Alive Power ..................................................................................................3.48

Rollovers In Time ...................................................................................................................3.49

Received Carrier To Noise Density Ratio (C/NO) .............................................................3.50

Motorola GPS Products - Oncore User’s Guide

Revision 5.0 08/30/02

3.3

Oncore

Chapter 3 – Receiver Description

OVERVIEW

The Oncore receiver provides position, velocity, time, and satellite tracking status information via a serial port.

A simplified functional block diagram of the Oncore receiver is shown in the following illustration.

Figure 3.1: Oncore Receiver Functional Block Diagram

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Simplified Block

Diagram Description

Warning

Chapter 3 – Receiver Description

OVERVIEW (CONTINUED)

The Oncore Receiver has an eight channel design (12-channel design for the

M12+) capable of tracking eight (twelve for M12+) satellites simultaneously. The module receives the Ll GPS signal (1575.42 MHz) from the antenna and operates off the coarse/acquisition (C/A) code tracking. The code tracking is carrier aided. The

Oncore receiver must be powered with regulated +5 V (Nominal 3V for M12+) power.

Time recovery capability is inherent in the architecture. The UT Oncore is designed specifically for precise timing applications.

The Ll band signals transmitted from GPS satellites are collected by a low-profile, microstrip patch antenna, passed through a narrow-band bandpass filter, and then amplified by a signal preamplifier contained within the antenna module. Filtered and amplified Ll band signals from the antenna module are then routed to the RF signal processing section of the receiver module via a single coaxial interconnecting cable.

This interconnecting cable also provides the +5 V (Nominal 3V for M12+) power required for signal pre-amplification in the antenna module.

The RF signal processing section of the Oncore receiver printed circuit board (PCB) contains the required circuitry for down-converting the GPS signals received from the antenna module. The resulting intermediate frequency (IF) signal is then passed to the eight channel code and carrier correlator section of the Oncore receiver PCB where a single, high speed analog-to-digital (AD) converter converts the IF signal to a digital sequence prior to channel separation. This digitized IF signal is then routed to the digital signal processor (also contained within the eight channel code and carrier correlator section) where the signal is split into eight parallel channels for signal detection, code correlation, carrier tracking, and filtering.

The processed signals are synchronously routed to the position microprocessor

(MPU) section. This section controls the GPS receiver operating modes and decodes and processes satellite data and the pseudorange and delta range measurements used to compute position, velocity, and time. In addition, the position processor section contains the inverted TTL serial interface.

Keep-alive random access memory (RAM) is provided for the retention of satellite ephemeris data, custom operating parameters, almanac information, and other information, as specified in Chapter 5. To prevent loss of this information when the

Oncore receiver is powered off, an external +5 V (Nominal 3V for M12+) BATT voltage is required. Retention of the real-time-clock (RTC) value also requires the external +5 V (Nominal 3V for M12+) BATT signal when the Oncore receiver is powered off.

Motorola GPS Products - Oncore User’s Guide

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Chapter 3 – Receiver Description

ANTENNA SENSE CIRCUIT

The Oncore receiver is capable of detecting the presence of an antenna. The receiver utilizes an antenna sense circuit that can detect under current (open condition), over current (shorted or exceeding maximum receiver limits), or a valid antenna connection. The antenna sense circuit was designed around the Motorola

GPS antenna; therefore non Motorola antennas may exceed the threshold limits as listed below

Under current circuit @ 25 degC:

Good indication: greater than 5 mA

Bad indication: less than 5 mA

Over current circuit @ 25 degC:

80 mA maximum for normal operation

45 mA maximum for short circuit

The above information is output in the following I/O messages, @@Ea (8-Channel

Position/Status/Data Output), @@Fa (8-Channel SelfTest), @@Ha

(Position/Status/Data 12-Channel), @@Ia (Self-Test Message 12-Channel). Upon detecting an over current situation, the receiver will automatically shut down the antenna feed section until the fault is cleared. Upon detecting an under current situation, the receiver will continue to operate as normal, but will flag the fault mode in the two 1/O messages. An external power source must be used if the antenna circuit power requirements exceed the limits.

ANTENNA FEED CURRENT

The Oncore receiver now provide up to 80 mA of current via the antenna power supply circuit. The circuit still has a short protection and a means for detecting over current and open circuit conditions of the connection between it and the antenna.

This allows the user a degree of confidence that the antenna is connected and drawing current. This feature can eliminate hours of troubleshooting, especially in a new installation.

The antenna power supply circuit consists of a current sense resistor, two rail to rail operational amplifiers, a pass transistor and a voltage divider to set the upper and lower limits of the under current and over current thresholds. The operational amplifiers compare the voltage developed across the current sense resistor with these thresholds. if the antenna is drawing 5 mA or more, the first operational amplifier will produce a logic level to the digital circuits where it is monitored by the firmware. if the signal is absent, indicating an under current condition, an alarm bit is set to alert the user.

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Chapter 3 – Receiver Description

Antenna Feed Circuit

(Continued)

For the over current circuit, when the voltage drop across the current sense resistor is equal to the over current threshold (set at about 90 mA for room temperature) the output of the amplifier starts shutting down the pass transistor. At this point, the voltage to the antenna starts to decrease and a logic level is provided for the digital circuit to trigger an alarm bit that indicates an overcurrent condition.

Figure: 3.2

An additional feed back path between this output voltage and the over current operational amplifier causes a further decrease in the output current depending on the output voltage level. This action results in folding back the current such that the short circuit amount is about 45 mA, which is less than the 90 mA threshold. This prevents the over heating of the series pass transistor should the shorted coax condition occur. A chart of the typical output voltage vs. the load current is shown in figure 3.2 above.

The output current limit is higher than previous versions of Oncore receivers. This is to support longer cable runs through the use of higher gain antennas or in-line amplifiers so that the signal does not drop below the tracking threshold when it reaches the GPS receiver.

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3.7

External Gain Range

Chapter 3 – Receiver Description

ACTIVE ANTENNA CONFIGURATION

The recommended external gain (antenna gain minus cable and connector losses) for the GT Oncore R3 model is 10 to 26 dB. The recommended external gain for the UT

Oncore R5 model is 10 to 33 dB. A typical antenna system might have an active antenna with 24 dB of gain and six meters of cable with 6 dB of loss. The external gain would then be 18 dB, which is within the acceptable range. For more information, refer to the Active Antenna Applications Note.

Motorola GPS Products - Oncore User’s Guide

Revision 5.0 08/30/02

Figure 3.3: Oncore Receiver

3.8

Chapter 3 – Receiver Description

M12+ AND M12+ TIMER ONCORE RECEIVER ELECTRICAL

CONNECTIONS

The M12+ and M12+ Timer receives electrical power and receives/transmits I/O signals through a 10pin power/data connector mounted on the Oncore. Refer to

Figure 3.3 for pin numbering.

The following table lists the assigned signal connections of the Oncore receiver's power/data connector. For more information, refer to the Active Antenna

Applications Note.

Table 3.1: Oncore Power/Data Connector Pin Assignments

6

7

8

Pin #

1

2

3

Signal Name

TTL TXD1

TTL RXD1

+3V PWR

Description

Transmit 3V logic

Receive 3V logic

Regulated main power

4 1PPS One per pulse per second signal

5 GROUND Ground

BATTERY

Reserved

RTCM IN

Externally applied backup power

Not currently used

RTCM input only

9 Antenna Voltage 3 V to 5 V antenna input voltage

10 Reserved Not currently used

Oncore Operation Voltage And Current Ranges

3V PWR (Main power)

Voltage: 2.85V to 3.15V regulated

Current: 0.225 W maximum (without antenna)

BATTERY (Externally applied backup power)

Voltage:

Current:

Retention

2.2V to 3.2V

5 uA typical @ 2.7V @25 degC

Backup power retains date, time, position, satellite data, oscillator learning table and operating mode.

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Chapter 3 – Receiver Description

M12+ ONCORE RECEIVER PRINTED CIRCUIT BOARD

Figure 3.4: M12+ and M12+ Timer Oncore Printed Circuit Board Layout

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3.10

PERFORMANCE

CHARACTERISTICS

SERIAL

COMMUNICATION

ELECTRICAL

CHARACTERISTICS

PHYSICAL

CHARACTERISTICS

ENVIRONMENTAL

CHARACTERISTICS

NOTES

Chapter 3 – Receiver Description

M12+ ONCORE RECEIVER TECHNICAL CHARACTERISTICS

Table 3.2: Oncore Technical Characteristics – M12+ Model

GENERAL

CHARACTERISTICS

MISCELLANEOUS

Receiver Architecture

Tracking Capability

Dynamics

Acquisition Time

(Time To First Fix, TTFF)

(Tested at –30 to +85ºC)

Positioning Accuracy

12 channel

L1 1575.42 MHz

C/A code (1.023 MHz chip rate)

Code plus carrier tracking (carrier aided tracking)

12 simultaneous satellite vehicles

Velocity: 1000 knots (515 m/s) > 1000 knots (515 m/s); at altitudes < 60,000 ft. (18,000m)

Acceleration: 4g

Jerk: 5 m/s 3

Vibration: 7.7G per Military Standard 810E

15s typical TTFF-hot (with current almanac,position,time and ephemeris)

40s typical TTFF-warm (with current almanac, position, and time)

60s typical TTFF-cold (no stored information)

< 1.0s internal reacquisition (typical)

100 meters 2dRMS with SA as per DoD specification

Less than 25 m SEP without SA

Timing Accuracy

(1 Pulse per second, 1 PPS)

Antenna Requirements

Datum

Output Messages

Power Requirements

“Keep-Alive” BATT Power

Power Consumption

Dimensions

Weight

Connectors

< 500nS with SA on

Active antenna module powered by receiver module

18dB to 36dB external antenna gain measured at input to receiver

3 V or 5 V Antenna power provided via header connector

WGS-84 Default

One user definable datum

Latitude, longitude, height, velocity, heading, time

Motorola binary protocol at 9600 baud

NMEA 0183 at 4800 baud (GGA,GLL, GSV, RMC, VTG, ZDA)

Software selectable output rate (continuous or poll)

TTL interface (0 to 3 V)

Second COM port for RTCM input

2.85 to 3.15 Vdc; 50 mVp-p ripple (max)

External 2.2 Vdc to 3.2 Vdc, 5 uA typical @ 2.7 Vdc @ 25ºC

< 185mW @ 3 V without antenna

40.0 x 60.0 x 10.0 mm (1.57 x 2.36 x 0.39 in.)

Receiver 25 g (0.9 oz.)

Active Antenna Module < 40 g

Data/power: 10 pin (2 x 5) unshrouded header on 0.050 in.

centers (available in right angle or straight configuration)

RF: right angle MMCX (subminiature snap-on)

Antenna to Receiver

Interconnection

Operating Temperature

Storage Temperature

Humidity

Altitude

Single coaxial cable

Antenna sense circuit

-40ºC to +85ºC

-40ºC to +105ºC

95% over dry bulb range of +38ºC to +85ºC

18,000 m (60,000 ft.) maximum

> 18,000 m (60,000 ft.) for velocities

< 515 m/s (1000 knots)

Standard Features Motorola DGPS corrections at 9600 baud on COM port one

RTCM SC-104 input Type 1 and Type 9 messages for DGPS at 2400, 4800 or 9600 baud on COM port two

NMEA 0138 output

Inverse DGPS support

Optional Features Lithium battery backup

All specifications typical and quoted at 25°C unless otherwise specified

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Chapter 3 – Receiver Description

M12+ TIMER ONCORE RECEIVER TECHNICAL CHARACTERISTICS

Table 3.2: Oncore Technical Characteristics – M12+ Timer Model

GENERAL

CHARACTERISTICS

PERFORMANCE

CHARACTERISTICS

SERIAL

COMMUNICATION

ELECTRICAL

CHARACTERISTICS

PHYSICAL

CHARACTERISTICS

ENVIRONMENTAL

CHARACTERISTICS

MISCELLANEOUS

NOTE

Receiver Architecture

Tracking Capability

Dynamics

Acquisition Time

(Time To First Fix, TTFF)

(Tested at –30 to +85ºC)

Positioning Accuracy

Timing Accuracy

(1 Pulse per second or, 100 PPS)

Position hold mode active

Antenna Requirements

Datum

Output Messages

12 channel

L1 1575.42 MHz

C/A code (1.023 MHz chip rate)

Code plus carrier tracking (carrier aided tracking)

12 simultaneous satellite vehicles

Velocity: 1000 knots (515 m/s) > 1000 knots (515 m/s); at altitudes < 60,000 ft.(18,000m)

Acceleration: 4g

Jerk: 5 m/s 3

Vibration: 7.7G per Military Standard 810E

200s TTFF-hot (with current almanac, position, time and ephemeris)

50s TTFF-warm (with current almanac, position, and time)

25s TTFF-cold (No stored information)

< 1.0s internal reacquisition (typical)

100 meters 2dRMS with SA as per DoD specification

Less than 25 m SEP without SA

Performance using clock granularity message*

< 2nS 1 Sigma average

< 6nS 6 Sigma average

Performance not using clock granularity message*

< 10nS 1 Sigma average

< 20nS 6 Sigma average

Active antenna module powered by receiver module

18dB to 36dB external antenna gain measured at input to receiver

3 V or 5 V Antenna power provided via header connector

WGS-84 Default

One user definable datum

Latitude, longitude, height, velocity, heading, time

Motorola binary protocol at 9600 baud

Software selectable output rate (continuous or poll)

TTL interface (0 to 3 V)

Power Requirements

“Keep-Alive” BATT Power

Power Consumption

Dimensions

Weight

2.85 to 3.15 Vdc; 50 mVp-p ripple (max)

External 2.2 Vdc to 3.2 Vdc, 5 uA typical @ 2.7 Vdc @ 25ºC

<185mW @ 3 V without antenna

40.0 x 60.0 x 10.0 mm (1.57 x 2.36 x 0.39 in.)

Receiver 25 g (0.9 oz.)

Active Antenna Module < 40 g

Connectors

Antenna to Receiver

Interconnection

Operating Temperature

Data/power: 10 pin (2 x 5) unshrouded header on 0.050 in.

centers (available in right angle or straight configuration)

RF: right angle MMCX (subminiature snap-on)

Single coaxial cable

Antenna sense circuit

Storage Temperature

Humidity

Altitude

-40ºC to +85ºC

-40ºC to +105ºC

95% over dry bulb range of +38ºC to +85ºC

Standard Features

18,000 m (60,000 ft.) maximum

> 18,000 m (60,000 ft.) for velocities

< 515 m/s (1000 knots)

Motorola Binary Protocol

Position hold with automatic site survey

Clock Granularity Error Message

T-RAIM (Timing Receiver Autonomous

Integrity Monitoring)

Optional Features Lithium battery backup

All specifications typical and quoted at 25°C unless otherwise specified

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Chapter 3 – Receiver Description

GT+, UT+, SL ONCORE RECEIVER ELECTRICAL CONNECTIONS

The Oncore receives electrical power and receives/transmits I/O signals through a

10pin power/data connector mounted on the Oncore Refer to Figure 3.3 for pin numbering.

The following table lists the assigned signal connections of the Oncore receiver's power/data connector. For more information, refer to the Active Antenna

Applications Note.

Table 3.3: Oncore Power/Data Connector Pin Assignments

5

6

7

8

9

Pin #

1

2

Signal Name

BATTERY

+5V PWR

Description

Externally applied backup power (< + 5V)

+5V regulated main power

3 GROUND Ground

4 VPP Flash memory programming voltage

RTCM IN

1PPS

1PPS RTN

TTL TXD

TTL RXD

RTCM input

One per pulse per second signal

One per pulse per second return

Transmit 5V logic

Receive 5V logic

10 TTL RTN Transmit/receive return

Oncore Operation Voltage And Current Ranges

5V PWR (Main power)

Voltage: 4.75 V to 5.25 V

Current: < 0.9 W at 5 V at 25øC with active antenna drawing 20 mA

BATTERY (Externally applied backup power)

Voltage: 2.5 V to 5.25 V

Current: 5 uA typical @ 2.5 V

100 uA typical @ 5.0 V

Motorola GPS Products - Oncore User’s Guide

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Chapter 3 – Receiver Description

GT+, UT+, SL ONCORE RECEIVER PRINTED CIRCUIT BOARD

Figure 3.5: Oncore Printed Circuit Board Layout UT, GT and SL

Motorola GPS Products - Oncore User’s Guide

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Chapter 3 – Receiver Description

GT+ ONCORE RECEIVER TECHNICAL CHARACTERISTICS

Table 3.4: Oncore Technical Characteristics – GT Plus Model

General

Characteristics

Receiver Architecture

Performance

Characteristics

Tracking Capability

Dynamics

Acquisition Time

(Time To First Fix, TTFF)

(Tested at –30 to +85ºC)

Positioning Accuracy

8 parallel channel

L1 1575.42 MHz

C/A code (1.023 MHz chip rate)

Code plus carrier tracking (carrier aided tracking)

8 simultaneous satellite vehicles

Velocity: 1000 knots (515 m/s); > 1000 knots at altitudes < 60,000 ft.

Acceleration: 4g

Jerk: 5 m/s 3

Vibration: 7.7G per Military Standard 810E

< 15 s typical TTFF-hot (with current almanac, position, time and ephemeris)

< 45 s typical TTFF-warm (with current almanac, position, and time)

< 90 s typical TTFF-cold

< 1.0 s internal reacquisition (typical)

100 m 2dRMS with SA as per DoD specification

Less than 25 m SEP without SA

1-5 m typical in differential mode

< 500 ns (1 sigma) with SA on

(1 Pulse Per Second, 1 PPS)

Antenna

Serial

Communication

I/O Messages

Electrical

Characteristics

Physical

Characteristics

Power Requirements

“Keep-Alive” BATT Power

Power Consumption

Dimensions

Weight

Connectors

Environmental

Characteristics

Antenna to Receiver

Interconnection

Operating Temperature

Humidity

Altitude

Miscellaneous

Datum

Optional Features

Active micro strip patch antenna module

Powered by receiver module (5-80 mA @ 5 V)

WGS-84

One user definable datum

Latitude, longitude, height, velocity, heading, time

Motorola binary protocol at 9600 baud

NMEA at 4800 baud: GGA, GLL., GSA, GSV, RMC, VTG,ZDA

Software selectable output rate (continuous or poll)

TTL interface (0 to 5 V)

Second COM port for RTCM input

5

± 0.25 V; 50 mVp-p ripple (max)

External 2.5 V to 5.25 V; 5 uA typical @ 2.5 V

<0.9 W @ 5 V with active antenna drawing 20 mA

2.00 x 3.25 x 0.64 in. (50.8 x 82.6 x 16.3 mm)

1.8 oz (51g)

Data/power: 10 pin (2x5) unshrouded header on 0.100 in, centers

RF: right angle OSX (subminiature snap-on)

Single coaxial cable

Antenna sense circuit

-40ºC to +85ºC

95% noncondensing +30ºC to +60ºC

60,000 ft. (18 km) (max.)

> 60,000 ft. (18 km) for velocities < 1000 knots

Motorola DGPS input corrections at 9600 baud on COM port one

RTCM SC-104 input Type 1 and Type 9 messages for DGPS at 2400, 4800, or

9600 baud on COM port two.

NMEA 0183 output

Velocity filtering (user controlled)

Lithium battery

Right angle SMB RF connector

On-board LNA for passive antenna support

Low profile shields

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Chapter 3 – Receiver Description

UT+ ONCORE RECEIVER TECHNICAL CHARACTERISTICS

Table 3.5: Oncore Technical Characteristics – UT Plus Model

General

Characteristics

Receiver Architecture

Performance

Characteristics

Tracking Capability

Dynamics

Acquisition Time

(Time To First Fix, TTFF)

(Tested at –30 to +85ºC)

Positioning Accuracy

(1 Pulse Per Second, 1 PPS)

Jamming Immunity

Antenna

Serial

Communication

Datum

Output Messages

Electrical

Characteristics

Physical

Characteristics

Power Requirements

“Keep-Alive” BATT Power

Power Consumption

Dimensions

Weight

Connectors

Environmental

Characteristics

Antenna to Receiver

Interconnection

Operating Temperature

Humidity

Altitude

Miscellaneous Standard Features

Optional Features

8 parallel channel

L1 1575.42 MHz

C/A code (1.023 MHz chip rate)

Code plus carrier tracking (carrier aided tracking)

8 simultaneous satellite vehicles

Velocity: 1000 knots (515 m/s); > 1000 knots at altitudes < 60,000 ft.

Acceleration: 4g

Jerk: 5 m/s

3

Vibration: 7.7G per Military Standard 810E

< 20 s typical TTFF-hot (with current almanac, position, time and ephemeris)

< 50 s typical TTFF-warm (with current almanac, position, and time)

< 300 s typical TTFF-cold

< 1.0 s internal reacquisition (typical)

100 m 2dRMS with SA as per DoD specification

Less than 25 m SEP without SA

Time RAIM algorithm

< 130 ns (1 sigma) with SA on

In position hold mode, < 50 ns (1 sigma) with SA on

Immune to the following CW Jamming signal levels measured at the input to the Oncore Active Antenna when the receiver is in position-hold mode.

Values are typical.

-50 dBm @ 1570 MHz

-79 dBm @ 1575.42 MHz

-56 dBm @ 1580 MHz

Active micro strip patch antenna module

Powered by receiver module (5-80 mA @ 5 V)

WGS-84

Latitude, longitude, height, velocity, heading, time (Motorola binary protocol)

Software selectable output rate (continuous or poll)

TTL interface (0 to 5 V)

5

± 0.25 V; 50 mVp-p ripple (max)

External 2.5 V to 5.25 V; 5 uA typical @ 2.5 V

<0.9 W @ 5 V with active antenna drawing 20 mA

2.00 x 3.25 x 0.64 in. (50.8 x 82.6 x 16.3 mm)

1.8 oz (51g)

Data/power: 10 pin (2x5) unshrouded header on 0.100 in, centers

RF: right angle OSX (subminiature snap-on)

Single coaxial cable

Antenna sense circuit

-40ºC to +85ºC

95% noncondensing +30ºC to +60ºC

60,000 ft. (18 km) (max.)

> 60,000 ft. (18 km) for velocities < 1000 knots

Time RAIM

100PPS output

Automatic site survey

Jamming protection)

Lithium battery

Straight OSX RF connector

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Chapter 3 – Receiver Description

SL ONCORE RECEIVER TECHNICAL CHARACTERISTICS

Table 3.6: Oncore Technical Characteristics – SL Model

General

Characteristics

Receiver Architecture

Performance

Characteristics

Tracking Capability

Dynamics

Acquisition Time

(Time To First Fix, TTFF)

(Tested at –30 to +85ºC)

Positioning Accuracy

8 parallel channel

L1 1575.42 MHz

C/A code (1.023 MHz chip rate)

Code plus carrier tracking (carrier aided tracking)

8 simultaneous satellite vehicles

Velocity: 1000 knots (515 m/s); > 1000 knots at altitudes < 60,000 ft.

Acceleration: 4g

Jerk: 5 m/s

3

Vibration: 7.7G per Military Standard 810E

< 15 s typical TTFF-hot (with current almanac, position, time and ephemeris)

< 45 s typical TTFF-warm (with current almanac, position, and time)

< 90 s typical TTFF-cold

< 1.0 s internal reacquisition (typical)

100 m 2dRMS with SA as per DoD specification

Less than 25 m SEP without SA

1-5 typical in differential mode

< 500 ns (1 sigma) with SA on

(1 Pulse Per Second, 1 PPS)

Antenna

Serial

Communication

Output Messages

Electrical

Characteristics

Physical

Characteristics

Power Requirements

“Keep-Alive” BATT Power

Power Consumption

Dimensions

Weight

Connectors

Environmental

Characteristics

Antenna to Receiver

Interconnection

Operating Temperature

Humidity

Altitude

Miscellaneous

Datum

Optional Features

Active micro strip patch antenna module

Powered by receiver module (5-80 mA @ 5 V)

WGS-84

One user definable datum

Latitude, longitude, height, velocity, heading, time

Motorola binary protocol at 9600 baud

NMEA at 4800 baud: GGA, GLL, GSA, GSV, RMC, VTG, ZDA

Software selectable output rate (continuous or poll)

TTL interface (0 to 5 V)

Second COM port for RTCM input

5

± 0.25 V; 50 mVp-p ripple (max)

External 2.5 Vdc to 5.25 Vdc; 5 uA typical @ 2.5 Vdc

<0.9 W @ 5 Vdc with active antenna drawing 20 mA

40 x 80 x 12.2 mm (1.58 x 3.15 x 0.48 in.)

0.8 oz (22 g)

Data/power: 10 pin (2x5) unshrouded header on 0.050 in,. centers

RF: right angle OSX (subminiature snap-on)

Single coaxial cable

Antenna sense circuit

-40ºC to +85ºC

95% noncondensing +30ºC to +60ºC

60,000 ft. (18 km) (max.)

> 60,000 ft. (18 km) for velocities < 1000 knots

Motorola DGPS input corrections at 9600 baud on COM port one

RTCM SC-104 input Type 1 and Type 9 messages for DGPS at 2400,

4800, or 9600 baud on COM port two..

NMEA 0183 output

Velocity filtering (user controlled)

Inverse DGPS support

Straight 10 pin data/power connector

Right angle SMB RF connector

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1PPS SIGNAL DEFINITION

0 to 5 V live pulse (0 to 3 V for M12+)

1 PPS time mark is synchronous with the mid point of the rising edge of the pulse rising from 0 V to 5 V

Rise time is approximately 20 to 30 ns

5 V pulse width is approximately 200 ms ± 1 ms

The falling edge will occur approximately 200 ms after the rising edge

Accurate to < 500 ns (1 sigma) in stand alone mode (with SA on)

UT Oncore accurate to < 130 ns (1 sigma) in stand alone mode (with SA on)

UT Oncore accurate to < 50 ns (1 sigma) in position-hold mode (with SA on)

RF JAMMING IMMUNITY (UT MODEL ONLY)

Many precise timing GPS installations require locating the GPS antenna at close range to radiating antennas such as cellular telephone, paging, or other wireless communications systems. Some of these transmitters may randomly cause the GPS receivers to lose lock on tracked satellites. This can be very disconcerting to the timing user since the system must rely on clock coasting' until the satellite signals are reacquired. Long coasting times require more expensive oscillators for the timing electronics in order to meet system specifications for holdover capability.

The GPS signal is broadcast at 1575.42 MHz with a bandwidth of +/- 1 MHz.

Experience has shown that receiver selectivity, or the ability to select only the GPS band of information and reject all other signals, is an important feature for GPS receivers, especially in cases such as those often encountered in timing applications.

To reduce the risk of unintentional jamming from high power out-of-band signals causing dropouts, additional filtering has been added to the UT Oncore. The desired result was achieved by working with various GPS L-band filter suppliers to develop filters that were small economical and had the desired characteristics.

The VP Oncore (the predecessor to the UT Oncore) with the best selectivity (B8 model) uses two L-band filters and a five pole first IF filter. Experience from this model was used to design the improved UT Oncore. Although the B8 design is effective, the bandwidth of the input filter on this model is comparatively wide and the low side roll off is not very steep. The image filter and the first IF filter are very effective and have been retained for the R5 model of the UT Oncore. The first L-band filter has been replaced with one with a narrower bandwidth and steeper low side roll off. In addition, a third L-band filter was added between the first filter and the image filter. The second IF filter has also been improved. The result is a GPS receiver with greatly improved selectivity, which is to say, better immunity to jamming signals.

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RF Jamming

Immunity

(continued)

Figure below compares the selectivity of the R5 model of the UT Oncore with the B8 model of the VP Oncore. An additional 30 dB of rejection (an improvement of 1000:1 in power) has been achieved at the first image O/S 110 dB). The improvement is 15 dB at the second image (J/S 87 dB). The jamming immunity of the GPS receiver and antenna system will be further improved with the additional margin provided by the filtering in the active antenna. Values are typical at 25 degC and a nominal gps power of –130 dBm.

Figure 3.6: Jammer Frequency (MHz)

Note: Jamming tests performed at 25 degC with a nominal gps signal power of –130 dBm at the RF input of the UT+

Adaptive Tracking Loops

Motorola has developed an innovative software technique to further improve the

Adaptive Tracking Loops jamming immunity of the UT Oncore receiver. The technique takes advantage of the fact that for precise timing applications, the receiver is not moving.

In mobile applications of GPS, the receivers must be able to track satellites under varying dynamics. Vehicle acceleration causes an apparent frequency shift in the received signal due to Doppler shift. In order to track signals through acceleration, the tracking loops are wide enough to accommodate the maximum expected vehicle acceleration and velocity. When the GPS receiver is stationary, the tracking loops do not need to be as wide in order to track the satellites.

In the UT Oncore 2.x firmware, the satellite tracking loops are narrowed once the receiver has acquired the satellites and reached a steady state condition. This adaptive approach allows the tracking loops to be narrowed for maximum interference rejection while not unduly compromising the rapid startup and acquisition characteristics of the UT Oncore.

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RF Jamming

Immunity (continued

Test results have demonstrated that this approach is effective at providing an additional 10 dB of jamming immunity both in the GPS band and out-of-band. The combined results of the additional filtering and the adaptive tracking loops in the UT

Oncore make it very effective at improving RF jamming immunity, thus making installation in timing applications more flexible and robust.

AUTOMATIC SITE SURVEY (UT MODEL ONLY)

The Automatic Site Survey mode simplifies system design for static timing applications. This automatic position determination algorithm is user initiated and can be deactivated at any time.

The Automatic Site Survey averages a total of 10,000 valid 2D and 3D position fixes. If the averaging process is interrupted, the averaging resumes where it left off when tracking resumes. During averaging, bit 5 of the DOP type field in the

Position/Status/Data Message (@@Ea) is set. Once the position is surveyed, the UT

Oncore automatically enters the Position-Hold Mode. At this point, the auto survey flag is cleared and the normal position-hold flag is set in the receiver status byte of the @@Ea message. Once the antenna site has been surveyed in this manner, the user can expect a 2D position error of less than 10 m with 95% confidence and a 3D error of less than 20 m with 95% confidence.

Throughout the survey time the Time RAIM algorithm is active (if enabled) and is capable of detecting satellite anomalies, however isolation and removal of the bad measurement is not possible. Once the survey is completed, the Time RAIM algorithm is capable of error detection, isolation, and removal.

The status of the Automatic Site Survey and Position-Hold Mode is retained in RAM when the receiver is powered down only if battery backup power is provided.

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Chapter 3 – Receiver Description

100PPS OUTPUT (UT MODEL ONLY)

With the UT Oncore 2.x firmware, the timing output can be selected between 1PPS and 100PPS. This is done using the Pulse Mode command (@@AP). See chapter 6 for information on the format of this command.

When selected, the 100PPS signal is output on the same pin as the 1PPS. The 100PPS signal has the same accuracy and stability characteristics as the 1PPS signal. Each pulse is approximately 2-3 ms in duration (the pulse width is not accurately controlled) so the 100PPS signal has a nominal duty cycle of approximately 25%.

Every hundredth pulse is 6-7 ms in duration. The leading edge of the pulse following the long pulse corresponds to the top of the second (UTC or GPS, depending on the

Time Mode). Figure 3.7 shows a diagram of the 100PPS output signal.

The 1PPS Offset and 1PPS Cable Delay features work the same in 100PPS mode as they do in 1PPS mode. In 100PPS mode, these commands are used to accurately control the placement of the pulse after the long pulse.

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Chapter 3 – Receiver Description

TIME RAIM ALGORITHM DESCRIPTION (M12 TIMING AND UT

MODELS ONLY)

Time Receiver Autonomous Integrity Monitoring (RAIM) is an algorithm in the Oncore timing GPS receivers (M12 Timing and UT) that uses redundant satellite measurements to confirm the integrity of the timing solution. The RAIM approach is borrowed from the aviation community where integrity monitoring is safety critical.

In most surveying systems and instruments, there are more measurements taken than are required to compute the solution. The excess measurements are redundant.

A system can use redundant measurements in an averaging scheme to compute a blended solution that is more robust and accurate than using only the minimum number of measurements required. Once a solution is computed, the measurements can be inspected for blunders. This is the essence of Time RAIM. In order to perform precise timing, the GPS receiver position is determined and then the receiver is put into position-hold mode where the receiver no longer solves for position. With the position known, the time is the only remaining unknown. In order to compute the time, the GPS receiver only requires one satellite. If multiple satellites are tracked, then the time solution is based on an average of the satellite measurements.

When the average solution is computed, it is compared to each individual satellite measurement to screen for blunders. A residual is computed for each satellite by differencing the solution average and the measurement. If there is a bad measurement in the set, then the average will be skewed and one of the measurements will have a large residual.

If the magnitude of the residuals exceeds the expected limit, then an alarm condition exists and the individual residuals are checked. The magnitude of each residual is compared with the size of the expected measurement error. If the residual does not fall within a defined confidence level of the measurement accuracy, then it is flagged as a blunder. Once a blunder is identified, then it is removed from the solution and the solution is recomputed and checked again for integrity.

A simple analogy can be used to demonstrate the concept of blunder detection and removal: a table is measured eight times using a tape measure. The measurements are recorded in a notebook, but one of the measurements is recorded incorrectly.

The tape measure has 2 mm divisions, so the one sigma reading error is about 1 mm.

This implies that 95% of the measurements should be within 2 mm of truth.

The measurements and residuals are recorded in the table on the following page.

From the residual list, it is clear that trial six was a blunder. With the blunder removed, the average and residuals are recomputed. This time, the residuals fall within the expected measurement accuracy.

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Trial

Chapter 3 – Receiver Description

Table 3.7: Blunder Detection Example

Measurement

(m)

Residual

(mm)

Status New Residual

(mm)

Average 10.0125 10.000

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Chapter 3 – Receiver Description

RECEIVER MODULE INSTALLATION

Your Oncore receiver has been carefully inspected and packaged to ensure optimum performance. As with any piece of electronic equipment, proper installation is essential before you can use the equipment.

When mounting the Oncore receiver board into your housing system, special precautions need to be considered.

INSTALLATION PRECAUTIONS AND CONSIDERATIONS

Before you install an Oncore receiver, please review the following precautions and considerations.

Electrostatic Precautions

The Oncore Receiver printed circuit boards (PCBs) contain parts and assemblies sensitive to damage by electrostatic discharge (ESD). Use ESD precautionary procedures when handling the PCB. Grounding wrist bands and anti-static bags are considered standard equipment in protecting against ESD damage.

Electromagnetic Considerations

The Oncore receiver PCBs contain a very sensitive RF receiver; you must observe certain precautions to prevent possible interference from the host system. Because the electromagnetic environment will vary for each OEM application, it is not possible to define exact guidelines to assure electromagnetic compatibility.

The frequency of GPS is 1.575 GHz. Frequencies or harmonics close to the GPS frequency may interfere with the operation of the receiver, desensitizing the performance. Symptoms include lower signal to noise values, longer TTFFs and the inability to acquire and track signals. In cases where RF interference is suspected, try moving the antenna away from the source of the interference.

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Chapter 3 – Receiver Description

Installer Caution

(Continued)

RF Shielding

The RF circuitry sections on the Oncore GPS receiver board are protected with a tin plate shield to guard against potential interference from external sources. When a design calls for the Oncore to be near or around RF sources such as radios, it is recommended that the Oncore be tested and tried in the target environment to identify potential interference issues prior to final design.

In worst case situations, the Oncore receiver PCB may require an additional enclosure in a metal shield to eliminate electromagnetic compatibility (EMC) problems..

Real-Time Clock (RTC)

When powered up, the RTC in the Oncore receiver will have an incorrect time unless it was previously set and maintained by external backup power. To ensure a faster time to first fix, the time, date, and GMT offset should be input if both the main power and battery backup power have been disconnected.

Thermal Considerations

The receiver operating temperature range is -40øC to +85øC, and the storage temperature range is -40øC to +105øC. The antenna operating range is-40øC to

+100øC. Before installation, you should perform a thermal analysis of the housing environment to ensure that temperatures do not exceed +85øC when operating

(+105øC stored). This is particularly important if air circulation in the installation site is poor, other electronics are installed in the enclosure with the Oncore receiver PCB, or the Oncore receiver PCB is enclosed within a shielded container due to electromagnetic interference (EMI) requirements.

Grounding Considerations

The GT and UT Oncore receivers now have a different grounding scheme than previous Oncore receivers for improved EMI/EMC performance. The RF shields on both sides of the module are connected to ground at multiple points. The ground plane of the receiver is connected to the four mounting holes.

For best performance, it is recommended that the mounting standoffs in the application be grounded. The GPS receiver will still function properly if it is not grounded via the mounting holes, but the shields may be less effective.

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Chapter 3 – Receiver Description

PCB Mounting

Hardware

ONCORE RECEIVER MOUNTING INSTRUCTIONS (GT+/UT+ ONLY)

Mounting Hardware Design Guidelines

For all the design validation and process validation tests that were conducted and completed successfully by Motorola, the Oncore PCBs were mounted on round or hex female threaded metal standoffs and screwed/tightened down with metal english or metric screws. The mounting standoffs are available with english or metric threads.

One of the key points in selecting the four standoffs that will mechanically hold and secure the Oncore PCB to the application PCB directly or indirectly is the diameter of the standoffs. Obviously the height of the standoff will be determined by the customers application. Recommended nominal diameter of the standoffs should be around 0.165 in. or 4.16 mm (See Figure 3.8).

These standoff should give ample space and clearance between the outside diameter of the standoff and the outside edge of the RF shields of the GT

Oncore, and the outside diameter of the standoff and the outside edge of the 10 pin header of the

GT Oncore.

If the recommended diameters of the standoff are not available, one can probably go higher with the next available diameter. See the following table for a suggested list of companies that carry standoffs equal or close to the recommended diameters. The maximum limit is around 0.212 in. or 5.38 mm diameter; at this point the standoffs are literally touching the RF shields of the Oncore.

Another important point to consider is the mating 10-pin receptacle on the application

PCB. When choosing this mating connector, one must be aware that the outer diameter of the standoffs should not come too close to this connector.

Obviously the height of the standoffs will be determined by the components that are populated on the application PCB, especially the height of the 10 pin receptacle.

See Figures 3.9 and 3.10 for recommended layouts of the standoffs and mating receptacles. Also see Figure 3.5 which is an outline drawing of the Oncore receiver.

The drawing describes the overall placement and height of large components and connectors populated on both sides of the Oncore PCB.

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Mounting Hardware (Continued)

The recommended screws for the standoffs that will secure the Oncore to the standoffs are metal screws with 4-40 threads or M3 threads. The nominal torque to assemble the Oncore PCB with screws to the standoffs is 6 in-lb each with a maximum of 7 and minimum of 5 in-lb. Washers are not required nor recommended for use with the Oncore PCB. All design and process validation testing was completed with metal screws mounted directly onto the PCB without washers.

Figure 3.8: Layout of the Oncore PCB cross section with reference to the standoff and screw

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Mounting Hardware

(Continued)

Chapter 3 – Receiver Description

Table 3.8: List of Threaded Standoff Suppliers

No. Company Name Part description of metal standoffs

Outside diameter

1 Keystone Electronic Corp.

Tel: 718-956-8900

Fax: 718-956-9040

Plain female standoffs 4-40 threads available in lengths from

0.250 to 1.0 in.

0.187 in. round or hex

Plain female standoffs M3x0.5 mm threads available in lengths from 5 to 25 mm

5 mm hex

2 RAF Electronics Hardware

Tel: 203-888-2133

Fax: 203-888-9860

Plain female standoffs 4-40 threads available in lengths from

0.250 to 1.0 in.

0.187 in. round

Plain female standoffs M3x0.5 mm threads available in lengths from 5 to 25 mm

4.5 mm hex

Manufacturing Corp.

Tel: 215-766-8533

Fax: 215-766=-0143

Self clinching female standoffs 4-

40 threads available in lengths from 0.250 to 1.0 in.

0.165 in. round

Self clinching female standoffs

M3x0.5 mm threads available in lengths from 5 to 25 mm

4.2 mm round

Design and Process Validation Test Information

Motorola has conducted numerous design and process validation tests for different versions of the Oncore. Mechanically, the Oncore dimensions are exactly the same for different versions (model numbers) of the Oncore PCB.

One of the key legs of the design validation is the thermal shock testing followed by vibration testing. In thermal shock testing the temperature cycles every hour from -

40øC to +85øC The units are put through anywhere from

300 to 500 cycles before going on to the vibration table where they are mounted on metal standoffs.

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Chapter 3 – Receiver Description

Mounting Hardware

(Continued)

Sturdiness and Reliability of Metal Standoffs

The Oncore PCB mounted on standoffs 0.375 or 0.500 in. long passed the vibration test successfully. The mechanical test is conducted in three axes, one hour each, at 7.7

Gs random vibration. In the final analysis this is a severe military specification as per

MILSTD 810E. After the vibration test leg of the design validation, the screws lose about 60% to 80% torque, which is expected as per design. Also, all the parts populated on both sides of the Oncore PCB remain soldered to the PCB with no loose connections.

Motorola has also conducted independent vibration tests such as the SAE J1455

Truck Cab spec. (1.04 Gs for four hours per axis) and the SAE J1211 Car Chassis spec.

(2.57 Gs for four hours per axis). Both of them passed successfully with the GT

Oncore PCB mounted on 0.375 in. high standoffs.

Motorola conducted independent mechanical shock tests at the 30 G level (10 ms duration) at least 100 times, which also passed successfully.

Design Worksheets

Given below in figures 3.9 and 3.10 are sample worksheets which show the Oncore and the application PCB mounted in two different ways. The purpose of these worksheets is to provide the reader with recommended design guidelines.

Figure 3.9: Sample layout of GPS Oncore PCB which is directly connected to the application PCB

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Mounting Hardware

(Continued)

Design Worksheets (Continued)

Chapter 3 – Receiver Description

Figure 3.10: Sample layout of GPS Oncore PCB and the application

PCB independently mounted on a baseplate

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Chapter 3 – Receiver Description

MEAN TIME BETWEEN FAILURE (MTBF)

The MTBFs for the Oncore family of GPS receivers have been computed using the methods, formulas, and database of MIL-HDBK-217.

Table 3.9: Oncore Receiver Mean Time Between Failure (MTBF)

Average temperature (

ºC)

VP Oncore

MTBF (hours)

GT/UT Oncore

MTBF (hours)

The above information is computed assuming a static application in a benign environment at the given temperatures. These reliability predictions only provide broad estimates of the expected random failure rates of the electrical components during the useful life of the product, and are not to be used as absolute indications of true field failure rates. The above MTBF values may not correspond to actual field failure rates.

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Chapter 3 – Receiver Description

Operational

Overview

Interface Protocol

Description

Format

Type

Direction

Port

Baud Rate

Parity

Data bits

Start/stop

SYSTEM INTEGRATION

The Motorola Oncore receiver is an intelligent GPS sensor intended to be used as a component in a precision positioning, navigation or timing system. The Oncore receiver is capable of providing autonomous position, velocity, and time information over a serial TTL port. The minimum usable system combines the Oncore receiver, antenna, and an intelligent system controller device.

INTERFACE PROTOCOL

The Motorola Oncore receiver has up to two TTL serial data ports. The first port is configured as a data communications equipment (DCE) port and provides the main control and data path between the Oncore receiver and the system controller. The second port is for RTCM DGPS correction input (M12+ and GT+ only). Refer to table below for the interface protocol parameters. To connect the Oncore to an RS-232 port, one must supply circuitry to convert TTL to RS-232 and RS-232 to TTL.

The I/O port operates under interrupt control. Incoming data is stored in a buffer that is serviced by the Oncore receiver's operating program. This buffer is serviced every

1.0 seconds.

Table 3.10: Oncore Interface Protocol

Binary ASCII 1 & 9

In/out In/out In/out

1 1 2

9600 4800 2400, 4800, 9600

None None None

8 8 8

1/1 1/1 1/1

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Chapter 3 – Receiver Description

TTL OUTPUT

The serial interface signals, RXD and TXD, are available for user connection. A ground signal is also required to complete the serial interface. There is no additional protection or signal conditioning besides the internal protection of the microprocessor since they are connected to the microprocessor directly. TXD and

RXD are regular TTL signals with voltage ranges from (0v-3v or 0v-5v depending on the receiver). For input signals, minimum input high voltage is 2 V and the maximum input high voltage is 5 V. Minimum input low voltage is 0 V and the maximum input low voltage is 0.8 V. For output signals, minimum output high voltage is 2.4 V and the maximum output low voltage is 0.5 V

This interface is not a conventional RS-232 interface that can connect to a PC (which are normally equipped with an RS232 interface) directly. An RS-232 driver/receiver is required to make this connection. The driver/receiver provides a voltage shift from 0 to 5 V to a positive and negative voltage (for example, ñ10 V), and also has an inversion process in it. Some RS-232 driver/receiver integrated circuits (ICs)-for example; Motorola's MC145407will provide all these functions with only a +5 V supply.

TTL 0 V to 0.8V = logic

RS-232

0 2.4 V to 5.0 V = logic 1

-5 V to -15 V = logic 1

5 V to 15 V = logic 0

NOTE: 50 pf maximum capacitance on TTL level output

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Motorola Binary Format

The binary data messages used by the Oncore Receiver consist of a variable number of binary characters. These binary messages begin with the ASCII @@ characters and are terminated with the ASCII carriage return and line feed <CR><LF>. The first two bytes after the @@ characters are two ASCII characters that identify the particular structure and format of the remaining binary data. The byte preceding the termination <CR><LF> of all messages is a single byte checksum (the exclusive-or of all message bytes after the @@ and before the checksum). Every message has the following components:

Message Start:

@@ - (two hex 40s) denotes start of binary message.

Message ID:

(A.Z(a..z, A..Z) - ASCII upper-case letter, followed by an ASCII lowercase or upper case letter. These two characters together identify the message type and imply the correct message length and format.

Binary Data Sequence:

Variable number of bytes of binary data dependent on the command type.

Checksum:

C - The exclusive-or of all bytes after the @@ and prior to the checksum.

Message Terminator:

<CR><LF> - carriage return and line feed denoting the end of the binary

message.

Every Oncore receiver input command has a corresponding response message so that you can determine whether the input commands have been accepted or rejected by the Oncore receiver. The message format descriptions in Chapter 6 detail the input command and response message formats. Information contained in the data fields is normally numeric. The interface design assumes that the operator display is under the control of an external system data processor and that display format and text messages reside in its memory. This approach gives you complete control of the display format and language.

The Oncore receiver reads the input command string on the input buffer once per second. If a full command has been received, then it operates on that command and performs the indicated function. Input character string checks are performed on the input commands. A binary message is considered to be received if it began with @@ and is terminated with a carriage return and a line feed, the message is the correct length for its type, and the checksum validates.

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Description of

Motorola Binary

Format (Continued)

Chapter 3 – Receiver Description

Motorola Binary Format (Continued)

You must take care in correctly formatting the input command. Pay particular attention to the number of parameters and their valid ranges. An invalid message could be interpreted as a valid unintended message. A beginning CSC, a valid checksum, a terminating carriage return line feed, the correct message length and valid parameter ranges are the only indicators of a valid input command to the

Oncore receiver. For multi-parameter input commands, the Oncore receiver will reject the entire command if one of the input parameters is out of range. Once the input command is detected, the Oncore receiver validates the message by checking the checksum byte in the message.

Input and output data fields contain binary data that can be interpreted as scaled floating point or integer data. The field width and appropriate scale factors for each parameter are described in the individual I/O message format descriptions. Polarity of the data (positive or negative) is described via the two's complement presentation.

Input command messages can be stacked into the Oncore receiver input buffer, up to the depth of the message buffer (

1200 characters long). The Oncore receiver will operate on all full messages received during the previous one second interval and will process them in the order they are received. Previously scheduled messages may be output before the responses to the new input commands.

Every input command has a corresponding output response message. This enables you to verify that the Oncore receiver accepted the input command. The Oncore receiver response to properly formatted commands with at least one out-of-range parameter is to return the previous unchanged value(s) of the parameter(s) in the response message.

Input commands may be of the type that change a particular configuration parameter of the Oncore receiver. Examples of these input command types include commands to change the initial position, the Oncore receiver internal time and date, satellite almanac, etc. These input commands, when received and validated by the Oncore receiver, change the indicated parameter and result in a response message to show the new value of the parameter that was changed. If the new value shows no change, then the input command was either formatted improperly, or one of the input parameters was out of its valid range.

NOTE: Every change-parameter type input command has a corresponding response message showing the configuration parameter change. To request the current status of the Oncore receiver, enter an input command with at least one out-of-range parameter. The response to properly formatted commands with out-of-range parameters is to output the original unchanged value of the parameter in the response message.

Input commands may also be of the type that enable or disable the output of data or status messages. These output status messages include those that the external controller will use for measuring position, velocity, and time.

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Motorola Binary Format (Continued)

Status messages are output at the selected update rate (typically, once per second) for those messages that contain position, velocity, or time, or can be commanded to output the data one time upon request. The rate at which the data is output in the continuous output mode is dependent on the type of data in the message. Table below shows the rates at which the data messages are output for each type of message, depending on the setting of the continuous/one-time option that is part of the input command.

Table 3.11: Data Message Output Rates

OUTPUT MESSAGE TYPE MSG.

ID

Ea

CONTINUOUS (m=1…255) ONE TIME

(m=0)

When requested Position/Status/Data Output

Message

ASCII Position Output

Message*

Time Raim Setup and Status

Message

Almanac Data Output

Visible Satellite Status

Message

UTC Offset Status**

Eq

En

Cb

Bb

At selected update rate

At selected update rate

At selected update rate

When new almanac available When requested

When visibility data changes When requested

Bo When UTC offset data available or when it changes

Leap Second Pending

Status

Bj Not available

*GT Oncore receiver only, **UT Oncore receiver only

When requested

When requested

When requested

When requested

For the case where more than one output message is scheduled during the same one second interval, the GPS receiver will output all scheduled messages but will attempt to limit the total number of bytes transmitted each second to

800 bytes. For the case of multiple output messages, if the next message to be sent fits around the

800 byte length goal, then the message will be output. For example, if messages totaling 7

58 bytes are scheduled to be sent, and the user requests another 58 byte message, then

816 bytes will actually be sent. If the user requests y et another 86 byte message, then its output will be left pending and will be scheduled when the total number of output bytes allows.

If external battery power is applied during the power-off state, the polled or continuous option of each output message is remembered in the Oncore receiver

RAM memory.

The UT Oncore timing receiver supports the timing capabilities via the Motorola binary I/O format. Non-timing receivers will not respond to, nor create, the timing I/O messages.

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Motorola Binary

Format Input/Output

Processing Time

NMEA Support

The GT Oncore 2.x firmware supports the NMEA 0183 format for GPS data output.

Output of data in the NMEA-0183 standard format allows a direct interface via the serial port to an electronic navigation instrument that supports the specific output messages. The following NMEA output messages are supported as per the NMEA-

0183 Specification Revision 2.0.1.

Message Description

GPGGA

GPGLL

GPS Fix Data

Geographic Position Latitude/Longitude

GPGSA

GPGSV

GPRMC

GPVTG

GPS DOP and Active Satellites

GPS Satellites in View

Recommended Minimum Specific GPS/Transit Data

Track Made Good and Ground Speed

You can enable or disable each message output independently and control the update rate at which the information is output. If back-up battery power is applied or if the receiver has the battery option, then the GT Oncore receiver retains the output settings when powered off and reconfigures itself to the same state when powered up again. If no back-up power is provided, the receiver will start up in the default state (Motorola binary format at 9600 baud) each time it is powered on.

All NMEA messages are formatted in sentences that begin with the ASCII $ (hex 24) and end with ASCII <CR><LF> (hex OD and hex OA). A five character address occurs after the ASCII $. The first two characters are the talker ID (which is GP for GPS equipment), and the last three characters are the sentence formatter or message ID from the list above. Note that the NMEA messages are not fixed length. Fields within the message are delimited by the ASCII comma character. The maximum length of any NMEA message is 79 characters.

The checksum is calculated by XORing the 8 data bits of each character in the sentence between, but not including, the $ and the optional (*) or checksum (CS). The high and low nibbles of the checksum byte are sent as ASCII characters.

The output of the above listed messages is controlled with a Motorola NMEA format message. Input messages follow the NMEA specification, and take the form

$PMOTG,,,,,*CS<CR><LF>. All input parameters are separated with comma delimiters.

The P character identifies the message as Proprietary format, the MOT is the manufacturer designator for Motorola, and the G is for GPS.

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NMEA 0183 Format

Overview

(Continued)

RTCM SC104 Format

Overview

For the case where more than one output message is scheduled during the same one second interval, the GPS receiver will output all scheduled messages but will attempt to limit the number of bytes transmitted each second to

400 bytes. For the case of multiple output messages, if the next message to be sent fits into the

400 byte length goal, then the message will be output. For example, if messages totaling 334 bytes are scheduled to be sent, and the user requests another 80 byte message, then

414 bytes will actually be sent. If the user requests yet another 70 byte message, then its output will not be generated. The order for priority for transmitting messages is simply alphabetical.

The NMEA input and output are on the primary serial port. For details on the command formats see the Input/Output section of this document.

RTCM Differential GPS Support

The M12+ and GT+ Oncore 2.x firmware supports the RTCM SC-104 format for differential corrections. The receiver employs a decoding algorithm that allows the unit to directly decode the RTCM Type 1 and Type 9 (6 of 8 type with two most significant bits always 01) differential correction messages from the secondary input serial port (pin 5). Having a separate port allows the M12+ and GT+ Oncore to simultaneously accept the RTCM format data stream and other receiver input commands (in either Motorola binary format or in NMEA format).

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EXCLUSIVE-OR CHECKSUM CREATION

This application note describes the procedure to calculate checksums used in the serial messages of the Oncore GPS receivers. An example message is used to illustrate the procedure.

Command name: Position/Status/Data Output Message (eight channel)

Command in Motorola binary format: @@EamC<CR><LF>

In this message, ‘m’ indicates the response message rate (ie. 1 = once per second, 2

= once every two seconds, etc.), and ‘C’ is the checksum. In calculating the checksum, only ‘Eam’ are used. The exclusive-or operation yields a one if only one of the bits is a one. Setting ‘m’ to ‘1’, we have the following:

Character Hexadecimal Binary

E 45 01000101 a 61 01100001

Xor 24 00100100

1 01 00000001

Xor 25 00100101

The final checksum would then be ‘25’ in hexadecimal. The complete command would then be as follows:

ASCII @ @ E a

Od Oa

^A % ^M ^J

To enter this command using the PC controller software type: @@Ea01

Within the PC controller software, the characters beyond the fourth character are treated as hexadecimal numbers and the checksum is computed automatically. The receiver will now report the eight channel position/status/data message every second. Note that this is equivalent to entering the ‘ps8 1’ controller command.

The checksum for the ASCII Position Message (@@Eq) is computed in a similar manner. The 8-bit checksum is converted to a decimal value between 0 and 255 and sent.

NMEA checksums, which are optional, are also calculated in a similar manner. The 8bit representations of all the characters between but not including the starting ‘$’ and the ending" are used. The high and low four bits of the eight bit checksum are converted to and sent as ASCII characters.

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MILLISECOND TO DEGREE CONVERSION

The primary output message of Oncore receivers is the Position/Status/Data

Message (@@Ea). In this message, the latitude and longitude are reported in milliarcseconds. This note describes how to convert milliarcseconds to degrees.

One degree of latitude or longitude has 60 arcminutes, or 3600 arcseconds, or

3,600,000 milliarcseconds.

To convert the positive or negative milliarcseconds to a conventional degrees, minutes, seconds format follow this procedure:

Divide the milliarcsecond value by 3,600,000

The integer portion of the quotient is the degrees

Multiply the remaining decimal fraction of the quotient by 60

The integer portion of the product is the minutes

Multiply the remaining decimal fraction of the product by 60

The integer portion of the product is the seconds

The remaining decimal fraction of the product is the decimal seconds

CONVERSION EXAMPLE:

Michigan Avenue, Chicago, IL:

Latitude = 150748869 mas

150748869 / 3600000 = 41.87468583 -315445441 / 3600000 = -87.62373361

0.87468583 * 60 = 52.48114980 -0.62373361 * 60 = 37.42401660

0.48114980 * 60 = 28.86898800 -0.42401660 * 60 = 25.44099600

Decimal seconds = 0.868988

Latitude = 41º 52'28.869"

Decimal seconds = 0.440996

Longitude = -87º 37'25.441"

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Motorola Binary

Format Input/Output

Processing time

Chapter 3 – Receiver Description

INPUT/OUTPUT PROCESSING TIME

The Oncore receiver always operates in position fix mode and the input buffer data is serviced once a second. When powered on and available satellites are tracked, the current receiver position is available. If no satellite signals are received, the last known position is output.

The message response time will be the time from the transmission of the first byte of input data to the transmission of the last byte of output data. The command processing time will be skewed since the time will be dependent on when the input message buffer is processed. For best case processing, the input command would have to arrive just before the input buffer data is processed, and the output response would have to be the first (or only) receiver output. For worst case processing, the input command would have to arrive just after the input buffer data had been processed, and the output response would have to be the last receiver output.

Assuming 1 ms per transmission of a data byte, assuming 50 ms command processing, and assuming a uniform distribution for time of input command data entry, the best case, typical case, and worst case scenarios are shown below.

Best case GMT Offset command:

BC time = shortest command input + command processing +

= 10 ms +50 ms +10 ms

Typical case:

TC time = input anywhere across one second period + command processing + output anywhere across one second

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Worst case:

WC time = input beginning of one second period + output end of

= 1 s+1 s =

Note: The receiver Self-Test command takes 5-10 seconds to complete.

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DATA LATENCY

The Oncore receiver can output position, velocity, and time data on the TTL port once each second. The start of the output data is timed to closely correspond with the receiver measurement epoch. The measurement epoch is the point in time at which the receiver makes satellite range measurements for the purpose of computing position. The first byte of TTL data in the position message is output between 0 and 50 ms after the most recent Oncore receiver measurement epoch.

Refer to Figure 3.11 for the discussions that follow.

Let T k

be the most recent measurement epoch. The Oncore Receiver takes about one second to compute data from the satellite range measurements. Consequently, the data output 0 to 50 ms after T k

represents the best estimate of the position, velocity, and time based on the measurements taken one second in the past, at time T k

_1. Position data (latitude, longitude, and height) is computed from the most recent measurement epoch data, and is output immediately after the next measurement epoch, which is 1.0 to 1.05 seconds after the original measurements were taken.

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DATA LATENCY (CONTINUED).

Chapter 3 – Receiver Description

Figure 3.11: Position/Status/Data Output Message Latency

To compensate for the one second computational pipeline delay, a one second propagated position is computed that corresponds to T k

based on the position and velocity data computed from measurements taken at time T k -1

. In this way, the position data output on epoch T k

will most closely correspond with the receiver true position when the data is output on the TTL port. Of course, there can be a position error due to the propagation process if the receiver is undergoing acceleration. The error can be as large as 4.5 m for every G of acceleration. There is no significant error under stationary or constant velocity conditions.

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Position DATA Latency

The position data output in the current data packet (i.e., at time T k

) is the result of a least squares estimation (LSE) algorithm using satellite pseudorange measurements taken at time T k-1

. The resulting LSE position corresponding to time T k-1

is then propagated one second forward by the velocity vector (the result of an LSE fit using satellite pseudorange rate measurements taken at T k-1

). The resulting propagated position is output at the T k

epoch.

Velocity DATA Latency

The velocity data output in the current data packet (i.e., at time T k

) is the result of an

LSE fit using satellite pseudorange rate measurements taken at time T k-1

. The pseudorange rate measurements are derived from the difference in integrated carrier frequency data sampled at measurement epochs T k-1

and T k-1

-200 ms. In effect, the resulting velocity data represents the average velocity of the receiver halfway between T k-1

and T k-1

-200 ms.

Time DATA Latency

The time data output in the current data packet (i.e., at time T k

) is the result of an LSE fit using satellite pseudorange measurements taken at time T k-1

The time estimate at

T k-1

is then propagated by one second plus the computed receiver clock bias rate at time T k-1

before being output at time T k

. The resulting time data is the best estimate of local time corresponding to the T k

measurement epoch based on data available at T k-1

ONE PULSE PER SECOND (1PPS) TIMING

Measurement Epoch Timing

The Oncore receiver timing is established relative to an internal, asynchronous, 1 kHz clock derived from the local oscillator. The receiver counts the 1 kHz clock cycles, and uses each successive 1000 clock cycles to define the time when the measurement epoch is to take place. The measurement epoch is the point at which the receiver captures the pseudorange and pseudorange rate measurements for computing position, velocity, and time.

When the receiver starts, it defines the first clock cycle as the measurement epoch.

Every 1000 clock cycles from that point define the next measurement epoch. Each measurement epoch is about one second later than the previous measurement epoch, where any difference from 1.000000000 seconds is the result of the receiver local oscillator intentional offset (about +

60 us/s) and the oscillator's inherent instability (+/-30 ppm over specified temperature range).

When the Oncore processor computes receiver local time, this time corresponds to the time of the last receiver measurement epoch. This time is precisely known by the

Oncore process to an accuracy of approximately 20 to 300 ns depending on satellite geometry and the effects of selective availability.

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The computed time is relative to UTC or GPS time depending on the time type as specified by the user by the Time Mode.

The Oncore system timing is designed to slip time when necessary in discrete one millisecond intervals so that the receiver local time corresponds closely to the measurement epoch offset. The Oncore observes the error between actual receiver local time and the desired measurement epoch offset and then slips the appropriate integer milliseconds to place the measurement epoch to the correct integer millisecond. When a time skew occurs (such as after initial acquisition or to keep time within limits due to local oscillator drift), the receiver lengthens or shortens the next processing period in discrete one millisecond steps.

The rising edge of the 1PPS signal is the time reference. The falling edge will occur approximately 200 ms (+/-1 ms) after the rising edge. The falling edge should not be used for accurate time keeping.

Output Data Timing Relative To Measurement Epoch

Figure 3.12: Output Signal Timing

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Chapter 3 – Receiver Description

Output Data Timing Relative to Measurement Epoch (Continued)

The Position/Status/Data Message and the

Time RAIM Setup and Status Message are the only output messages containing time information. If enabled, these messages will be output from the receiver shortly after a measurement epoch. Generally, the first data byte in the first message will be output between 0 to 50 ms after a measurement epoch. For the Position/Status/Data

Message, the time output in the message reflects the best estimate of the most recent measurement epoch. A simple timing diagram is shown in figure 3.12.

IPPS Cable Delay and IPPS Offset (UT Model Only)

1PPS Cable Delay and 1PPS OfFset (M12 Timing and UT Model

Only)

Users can compensate for antenna cable length with the 1PPS Cable Delay command. The IPPS can also be positioned anywhere in the one second window using the 1PPS Offset command. The rising edge of the IPPS is placed so that it corresponds to the time indicated by the following equation:

1PPS rising edge time = top of second -1PPS cable delay + 1PPS offset

Consider the following example:

Top of second =

1PPS cable delay =

10.000000000 s

0.000654321 s

1PPS 0.100000000

1PPS rising edge time = 10.099345679 s

The rising edge of the IPPS signal is adjusted so that it occurs corresponding to the fractional part of time equal to the total above. The fractional part of time is measured relative to UTC or GPS time depending on the setting of the Time Mode.

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POWER-UP

STATE

OPERATIONAL CONSIDERATIONS

When powered on, the Oncore Receiver automatically acquires and tracks satellites; measures the pseudorange and phase data from each of up to eight satellites; decodes and collects satellite broadcast data; computes the Oncore receiver's position, velocity, and time; and outputs the results according to the current I/O configuration selected.

TTFF is a function of position uncertainty, time uncertainty, almanac age, and ephemeris age as shown in the table below. The following information assumes that the antenna has full view of the sky when turned on.

Table 3.12: GT+, UT+, SL Oncore TTFF Information

INITIAL ERROR AGE TTFF

(GT+)

TTFF

(M12+)

Hot

Warm

100 km

100km

3 min

3 min

1 month

1 month

<4 hrs

U/A

15s

45s

30s

65s

<15s

<40s

U/A – This parameter is assumed to be unavailable.

N/A – Not applicable. Knowledge of this parameter has no effect on TTFF in this configuration.

Reacquisition time for all GPS satellite signals after signal obscuration is a function of the obscuration time, as shown in the table below.

Table 3.13: Reacquisition Times

TIME OBSCURED

<15 s

15 s

60 s

30 min

REACQUISITION TIME (Typical)

<1.0 s internal

2.5 s

3.6 s

300 s

First Time On

When the Oncore receiver powers up for the first time after factory shipment, the initial date and time will be incorrect. This will force the Oncore receiver into a cold power-up state (cold start), and it will begin to search the sky for all available satellites. After one satellite has been acquired, the date and time will automatically be set using the satellite. When three or more satellites are tracked, automatic position computation is initiated. At power down, the Oncore receiver does not remember its current configuration unless external battery power is applied.

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Chapter 3 – Receiver Description

Initialization

When powered up, the On core receiver executes the satellite a cquisition and tracking algorithms and will compute position when it acquires at least three s atellites. Fo r each of the user-r eque stable outputs, the receiver (if ba ttery backed) re members t he prev iously requested message state (continuous or onetime) and ra te. If no me ssages were requested contin uously the last time the receiver was u sed, it waits for a n input command b efore it outputs any other data, even though it may have ac quired s atellites and is p ossibly computing position fixes internally.

The Oncore receiver does not need to be initialized to its approximate user position coordinates to acq uire satellites and output position, nor does it require a current satellite almanac. However, the TTFF will be considerably shorter if you help the

Oncore receiver find satellites by setting the approximate initial position coordinate s, setting the time and date correctly, and installing a recent satellite almanac.

If backup power is available, the Oncore receiver retrieves its last known position coordinates from RAM when main power is reapplied, and uses this information in the satellite acquisition algorithm. It also retrieves time and date information from the internal real-time clock so you do not have to initialize this information after you initially set the time or after it is obtained from the satellites. In addition, the receiver retains the almanac and last used satellite ephemeris as long as the backup power is applied. If you move the Oncore receiver a great distance before using it again, it will find and acquire satellites, but the TTFF will be longer than normal the first time you use the receiver. You can initialize the approximate position coordinates for faster

TTFF if desired.

Each message in the I/O format description in Chapter 6 shows the default value for each parameter.

Shut Down

It is recommended that the receiver not be shut down within 35 s of computing an initial 2D or 3D position fix. This allows for a full set of ephemerides to be downloaded to RAM, which may shorten the next startup time.

Keep Alive Power

If you disconnect the keep alive power (BATT power), then the real-time clock (RTC) and the battery backed RAM memory will be erased. In this scenario, date and time are lost and the Oncore receiver will enter the cold powerup state when power is reapplied. If the keep alive power is maintained during main power off, then the receiver will retain the last known position and time as well as the almanac, ephemeris, settings, and communications mode. If the receiver is turned on within four hours of power down, then a hot start condition may apply. Otherwise, a warm start condition will apply.

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ROLLOVERS I N TIME

In August of 1999, the GPS week number will rollover from 1023 to 0 due to the l imited length of the GPS week field in the navigation data stream. Motorola Oncore receivers (M12+, M12 Timing, GT+, UT+, VP, XT, and Basic) have been designed and tested to properly distinguish the correct 20 year window (1024 weeks is just shy o f 20 years). They will not need reprogramming or replacement come 1999. In fact, the transition will be completely transparent to users of Motorola Oncore GPS receivers .

Motorola Oncore GPS receivers are also year 2000 compliant.

Multichannel GPS satellite simulators have been used to test each rollover condition in GPS. For example, each week there is a rollover in the GPS seconds on midnight

Saturday. The August 1999, year 2000, leap day, and leap second rollovers have a ll been successfully tested using simulators.

In order to handle the 1999 rollover, Motorola GT and UT Oncore GPS receivers use a date stored in flash memory. For example, if the firmware date is 1998, a defaulted receiver that does not have back-up power (or battery) will start with an internal tim e of 12:00 on 1/1/98 and begin acquiring satellites. Once the first satellite is acquired, the time and week number will be downloaded from the navigation data message .

The receiver determines the current date by starting from the week number of 1/1/98

(week 938) and searching for the first occurrence of the current week number (week

964 for 7/1/98).

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Chapter 3 – Receiver Description

RECEIVED CARRIER TO NOISE DENSITY RATIO (C/NO)

The Position/Status/Data Message outputs C/No, which can be used to determine the relative signal levels of received satellite signals (refer to Figure below). C /No is the received carrier to noise density ratio. The units are dBHz, where No is the noise density ratio received in a 1 Hz bandwidth. The plot in Figure 3.13 is linear. The satellite signal strength is measured at the antenna input. Typically, the C/No is between 30 and 55 dB.

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Figure 3.13

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