Microchip Technology GPS-2700 User manual

2020 Microchip Technology Inc. DS50003016A
GPS-2700
User’s Guide

DS50003016A-page 2 2020 Microchip Technology Inc.
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GPS-2700 USER’S GUIDE
2020 Microchip Technology Inc. DS50003016A-page 3
Preface
NOTICE TO CUSTOMERS
All documentation becomes dated, and this manual is no exception. Microchip tools and
documentation are constantly evolving to meet customer needs, so some actual dialogs
and/or tool descriptions may differ from those in this document. Please refer to our website
(www.microchip.com) to obtain the latest documentation available.
Documents are identified with a “DS” number. This number is located on the bottom of each
page, in front of the page number. The numbering convention for the DS number is
“DSXXXXXXXXA”, where “XXXXXXXX” is the document number and “A” is the revision level
of the document.
For the most up-to-date information on development tools, see the MPLAB®IDE online help.
Select the Help menu, and then Topics, to open a list of available online help files.
PURPOSE OF THIS GUIDE
The GPS-2700 user guide provides basic recommendations for designing products to
use Microchip's GPS-2700. The guidelines in the document are generic because spe-
cific product requirements vary from one application to the other.
This material consists of a brief description of GPS-2700 design supported by block
diagrams, description of environmental issues, installation guidelines, and unit opera-
tion.
WHO SHOULD READ THIS GUIDE
This document is intended for engineers and telecommunications professionals who
are designing, installing, operating, or maintaining time, frequency, and synchroniza-
tion systems having a requirement for a low profile and highly precise frequency gen-
erator.
To use this document effectively, you should have a good understanding of digital tele-
communications technologies and analog frequency generation and synthesis tech-
niques.
DOCUMENT LAYOUT
This guide contains the following sections:
•Chapter 1. “Introduction”: Provides an overview of the product, describes the
major hardware and software features, and lists the system specifications.
•Chapter 2. “Quick-Start Instructions”: Contains the Principle of Operation,
Start-Up Sequence, and aspects related to first power-up.
•Chapter 3. “SCPI-Control Quick Start Instructions”: Provides an overview of
the telemetry interface and command structure.
•Chapter 4. “Firmware Upgrade Instructions”: Describes how to update the
GPS-2700 firmware.
•Chapter 5. “GPSCon Utility”: Contains information about using the GPSCon util-
ity for monitoring and control.

GPS-2700 User’s Guide
DS50003016A-page 4 2020 Microchip Technology Inc.
CONVENTIONS USED IN THIS GUIDE
This manual uses the following documentation conventions:
DOCUMENTATION CONVENTIONS
Description Represents Examples
Arial font:
Italic characters Referenced books MPLAB®IDE User’s Guide
Emphasized text ...is the only compiler...
Initial caps A window the Output window
A dialog the Settings dialog
A menu selection select Enable Programmer
Quotes A field name in a window or
dialog
“Save project before build”
Underlined, italic text with
right angle bracket
A menu path File>Save
Bold characters A dialog button Click OK
A tab Click the Power tab
N‘Rnnnn A number in verilog format,
where N is the total number of
digits, R is the radix and n is a
digit.
4‘b0010, 2‘hF1
Text in angle brackets < > A key on the keyboard Press <Enter>, <F1>
Courier New font:
Plain Courier New Sample source code #define START
Filenames autoexec.bat
File paths c:\mcc18\h
Keywords _asm, _endasm, static
Command-line options -Opa+, -Opa-
Bit values 0, 1
Constants 0xFF, ‘A’
Italic Courier New A variable argument file.o, where file can be
any valid filename
Square brackets [ ] Optional arguments mcc18 [options] file
[options]
Curly brackets and pipe
character: { | }
Choice of mutually exclusive
arguments; an OR selection
errorlevel {0|1}
Ellipses... Replaces repeated text var_name [,
var_name...]
Represents code supplied by
user
void main (void)
{ ...
}

Preface
2020 Microchip Technology Inc. DS50003016A-page 5
WARNINGS, CAUTIONS, RECOMMENDATIONS, AND NOTES
Warnings, Cautions, Recommendations, and Notes attract attention to essential or crit-
ical information in this guide. The types of information included in each are displayed
in a style consistent with the examples below.
WARNING
To avoid serious personal injury or death, do not disregard warnings. All warnings use
this style. Warnings are installation, operation, or maintenance procedures, practices,
or statements, that if not strictly observed, may result in serious personal injury or even
death.
CAUTION
To avoid personal injury, do not disregard cautions. All cautions use this style. Cau-
tions are installation, operation, or maintenance procedures, practices, conditions, or
statements, that if not strictly observed, may result in damage to, or destruction of, the
equipment. Cautions are also used to indicate a long-term health hazard.
Note: All notes use this style. Notes contain installation, operation, or mainte-
nance procedures, practices, conditions, or statements that alert you to
important information, which may make your task easier or increase your
understanding.
WHERE TO FIND ANSWERS TO PRODUCT AND DOCUMENT QUESTIONS
For additional information about the products described in this guide, please contact
your Microchip representative or your local sales office. You can also contact us on the
web at www.microsemi.com/ftdsupport.
When this manual is updated the latest version will be available for downloading from
Microchip’s web site. Manuals are provided in PDF format for ease of use. After down-
loading, you can view the manual on a computer or print it using Adobe Acrobat
Reader.
Manual updates are available at: www.microsemi.com/ftdsupport
RELATED DOCUMENTS AND INFORMATION
See your Microchip representative or sales office for a complete list of available docu-
mentation. To order any accessory, contact the Microchip Sales Department. See
www.microsemi.com/sales-contacts/0 for sales support contact information. If you
encounter any difficulties installing or using the product, contact Microchip Frequency
and Time Systems (FTS) Services and Support:
U.S.A. Call Center: including Americas, Asia and Pacific Rim
Frequency and Time Systems
3870 N 1st St.
San Jose, CA 95134
Toll-free in North America: 1-888-367-7966
Telephone: [phone]
Fax: [phone]

GPS-2700 User’s Guide
DS50003016A-page 6 2020 Microchip Technology Inc.
email: [email protected]
Internet: www.microsemi.com/ftdsupport
Europe, Middle East, and Africa (EMEA)
Microchip FTS Services and Support EMEA
Altlaufstrasse 42
85635 Hoehenkirchen-Siegertsbrunn
Germany
Telephone: [phone]
Fax: [phone]
email: [email protected]
email: [email protected]
THE MICROCHIP WEBSITE
Microchip provides online support via our website at www.microchip.com. This website
is used as a means to make files and information easily available to customers.
Accessible by using your favorite Internet browser, the website contains the following
information:
•Product Support – Data sheets and errata, application notes and sample
programs, design resources, user’s guides and hardware support documents,
latest software releases and archived software
•General Technical Support – Frequently Asked Questions (FAQs), technical
support requests, online discussion groups, Microchip consultant program
member listing
•Business of Microchip – Product selector and ordering guides, latest Microchip
press releases, listing of seminars and events, listings of Microchip sales offices,
distributors and factory representatives
CUSTOMER SUPPORT
Users of Microchip products can receive assistance through several channels:
• Distributor or Representative
• Local Sales Office
• Field Application Engineer (FAE)
• Technical Support
Customers should contact their distributor, representative or field application engineer
(FAE) for support. Local sales offices are also available to help customers. A listing of
sales offices and locations is included in the back of this document.
Technical support is available through the website at:
http://www.microchip.com/support.
DOCUMENT REVISION HISTORY
Revision A (July 2020)
• Initial release of this document as Microchip DS5000xxxxA.

GPS-2700 USER’S GUIDE
2020 Microchip Technology Inc. DS50003016A-page 7
Table of Contents
Preface ........................................................................................................................... 3
Purpose of This Guide........................................................................................... 3
Who Should Read This Guide............................................................................... 3
Document Layout .................................................................................................. 3
Conventions Used in this Guide ............................................................................ 4
Warnings, Cautions, Recommendations, and Notes............................................. 5
Where to Find Answers to Product and Document Questions .............................. 5
Related Documents and Information..................................................................... 5
The Microchip Website.......................................................................................... 6
Customer Support ................................................................................................. 6
Document Revision History ................................................................................... 6
Chapter 1. Introduction
1.1 Overview ....................................................................................................... 13
1.2 Operating Principles ...................................................................................... 13
1.3 General Safety Precautions .......................................................................... 14
1.3.1 Use an Approved Antenna Lightning Protector .......................................... 14
1.3.2 Grounding................................................................................................... 14
1.3.3 Power Connections .................................................................................... 14
1.3.4 Environmental Conditions........................................................................... 14
Chapter 2. Quick-Start Instructions
2.1 Powering Up the Unit .................................................................................... 15
2.2 Operating the Unit from a PC’s USB Port ..................................................... 15
2.3 Operating the Unit from the RS-232 Port ...................................................... 15
2.4 Major Connections ........................................................................................ 16
2.4.1 Harness Pinning ......................................................................................... 17
2.4.2 Harness Connectors J1 and J3 .................................................................. 18
2.4.3 Concurrent-GNSS Capabilities................................................................... 18
2.4.4 Connecting the GNSS Antenna.................................................................. 19
2.4.5 Connecting an LCD Display ....................................................................... 19
2.4.5.1 LCD Key ..................................................................................... 21
2.4.5.2 LCD Display Pages .................................................................... 21
2.5 Loop Parameter Adjustment.......................................................................... 25
2.6 Performance Graphs ..................................................................................... 26

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Chapter 3. SCPI-Control Quick Start Instructions
3.1 Introduction.................................................................................................... 31
3.2 General SCPI Commands............................................................................. 31
3.2.1 *IDN ............................................................................................................31
3.2.2 HELP?.........................................................................................................31
3.3 GPS Subsystem ............................................................................................ 31
3.3.1 GPS:SAT:TRA:COUN?...............................................................................32
3.3.2 GPS:SAT:VIS:COUN? ................................................................................32
3.3.3 NMEA Support ............................................................................................32
3.3.4 GPS:PORT <RS232 | USB>.......................................................................33
3.3.5 GPS:PORT? ...............................................................................................33
3.3.6 GPS:GPGGA <int> [0,255] .........................................................................33
3.3.7 GPS:GGAST <int> [0,255]..........................................................................33
3.3.8 GPS:GPRMC <int> [0,255] .........................................................................34
3.3.9 GPS:GPZDA <int> [0,255] ..........................................................................34
3.3.10 GPS:GPGSV <int> [0,255]........................................................................34
3.3.11 GPS:PASHR <int> [0,255] ........................................................................35
3.3.12 GPS:XYZSP <int> [0,255].........................................................................36
3.3.13 GPS:GNGGA <int> [0,255] .......................................................................36
3.3.14 GPS:GGAGNST <int> [0,255] ..................................................................36
3.3.15 GPS:GNRMC <int> [0,255].......................................................................37
3.3.16 GPS:GNZDA <int> [0,255]........................................................................37
3.3.17 GPS:DYNAM:MODE <int> [0,7]................................................................38
3.3.18 GPS:DYNAM:MODE 8 (Automatic Dynamic Mode) .................................39
3.3.19 GPS:DYNAM:STAT? ................................................................................39
3.3.20 GPS:REF:ADEL <float> <s | ns > [-32767ns,32767ns] ............................40
3.3.21 GPS:REF:PUL:SAW? ...............................................................................40
3.3.22 GPS:RESET ONCE ..................................................................................40
3.3.23 GPS:TMOD <ON | OFF | RSTSURV> ......................................................40
3.3.24 GPS:SURV ONCE ....................................................................................40
3.3.25 GPS:SURV:DUR <sec>............................................................................40
3.3.26 GPS:SURV:VAR <mm^2> ........................................................................41
3.3.27 GPS:HOLD:POS <cm, cm, cm> ...............................................................41
3.3.28 GPS:SURV:STAT? ...................................................................................41
3.3.29 GPS:INIT:DATE <yyyy,mm,dd>................................................................41
3.3.30 GPS:INIT:TIME <hour,min,sec> ...............................................................41
3.3.31 GPS:SYST:SEL [GPS | SBAS | QZSS | GAL | BD | GLO]........................41
3.3.32 GPS:NMEA:TALK <GP | GN> ..................................................................42
3.3.33 GPS:NMEA:SVN <GP | GN>....................................................................43
3.3.34 GPS:JAM? ................................................................................................43
3.3.35 GPS:FW?..................................................................................................43
3.3.36 GPS? ........................................................................................................43
3.4 GYRO Subsystem ......................................................................................... 43
3.4.1 GYRO:MODE <ON | OFF>.........................................................................44
3.4.2 GYRO:TRA <int> [0,255] ............................................................................44
3.4.3 GYRO:PORT <RS232 | USB>....................................................................44
3.4.4 GYRO:PORT? ............................................................................................44
3.4.5 GYRO:CAL <float,float,float,float,float,float> ..............................................44
3.4.6 GYRO:CAL:COMP......................................................................................45
3.4.7 GYRO:CAL:RESET ....................................................................................45

2020 Microchip Technology Inc. DS50003016A-page 9
3.4.8 GYRO:SENS <float,float,float>................................................................... 45
3.4.9 GYRO:GLOAD? ......................................................................................... 45
3.4.10 GYRO?..................................................................................................... 46
3.5 PTIME Subsystem......................................................................................... 46
3.5.1 PTIM:DATE? .............................................................................................. 46
3.5.2 PTIM:TIME? ............................................................................................... 46
3.5.3 PTIM:TIME:STR? ....................................................................................... 46
3.5.4 PTIM:TINT?................................................................................................ 46
3.5.5 PTIM:OUT <ON | OFF>.............................................................................. 46
3.5.6 PTIM:LEAP?............................................................................................... 47
3.5.7 PTIM:LEAP:PEND?.................................................................................... 47
3.5.8 PTIM:LEAP:ACC? ...................................................................................... 47
3.5.9 PTIM:LEAP:DATE? .................................................................................... 47
3.5.10 PTIM:LEAP:DUR?.................................................................................... 47
3.5.11 PTIM?....................................................................................................... 47
3.6 Synchronization Subsystem .......................................................................... 48
3.6.1 SYNC:HOLD:DUR?.................................................................................... 48
3.6.2 SYNC:HOLD:STAT? .................................................................................. 48
3.6.3 SYNC:HOLD:INIT....................................................................................... 48
3.6.4 SYNC:HOLD:REC:INIT .............................................................................. 49
3.6.5 SYNC:SOUR:MODE <GPS | EXT | AUTO>............................................... 49
3.6.6 SYNC:SOUR:STAT?.................................................................................. 49
3.6.7 SYNC:TINT?............................................................................................... 49
3.6.8 SYNC:IMME ............................................................................................... 49
3.6.9 SYNC:FEE?................................................................................................ 49
3.6.10 SYNC:LOCK?........................................................................................... 49
3.6.11 SYNC:OUT:1PPS:RESET <ON | OFF> ................................................... 49
3.6.12 SYNC:OUT:1PPS:RESET?...................................................................... 50
3.6.13 SYNC:OUT:1PPS:WIDTH <int> <ms | s > [200s,600ms] .................... 50
3.6.14 SYNC:OUT:FILT <ON | OFF>.................................................................. 50
3.6.15 SYNC:OUT:FILT?..................................................................................... 50
3.6.16 SYNC:HEA? ............................................................................................. 50
3.6.17 SYNC:TINT:THR <int> [50,2000] ............................................................. 51
3.6.18 SYNC?...................................................................................................... 51
3.7 DIAG Subsystem........................................................................................... 51
3.7.1 DIAG:ROSC:EFC:REL? ............................................................................. 51
3.7.2 DIAG:ROSC:EFC:ABS?............................................................................. 51
3.7.3 DIAG:LIF:COUN?....................................................................................... 52
3.7.4 DIAG?......................................................................................................... 52
3.8 Measure Subsystem...................................................................................... 52
3.8.1 MEAS:TEMP? ............................................................................................ 52
3.8.2 MEAS:VOLT?............................................................................................. 52
3.8.3 MEAS:CURR?............................................................................................ 52
3.8.4 MEAS:POW?.............................................................................................. 52
3.8.5 MEAS? ....................................................................................................... 52
3.9 System Subsystem........................................................................................ 53
3.9.1 SYST:COMM:SER:ECHO <ON | OFF> ..................................................... 53
3.9.2 SYST:COMM:SER:PRO <ON | OFF>........................................................ 53
3.9.3 SYST:COMM:SER:BAUD <9600 | 19200 | 38400 | 57600 | 115200> ....... 53
3.9.4 SYST:FACT ONCE .................................................................................... 53

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3.9.5 SYST:ID:SN? ..............................................................................................53
3.9.6 SYST:ID:HW? .............................................................................................53
3.9.7 SYST:LCD:CONT [0,1.0] ............................................................................53
3.9.8 SYST:LCD:CONT? .....................................................................................54
3.9.9 SYST:LCD:PAGE [0,8] ...............................................................................54
3.9.10 SYST:LCD:PAGE? ...................................................................................54
3.9.11 SYST:COMM:USB:BAUD <9600 | 19200 | 38400 | 57600 | 115200>......54
3.9.12 SYST:COMM:USB:BAUD?.......................................................................54
3.9.13 SYST:STAT? ............................................................................................54
3.10 Servo Subsystem ........................................................................................ 54
3.10.1 SERV:LOOP <ON | OFF> ........................................................................55
3.10.2 SERV:MODE <OFF | NORM | FAST | AUTO> .........................................55
3.10.3 SERV:STAT? ............................................................................................55
3.10.4 SERV:DACG <float> [0.001, 10000].........................................................55
3.10.5 SERV:EFCS <float> [0.0, 500.0]...............................................................56
3.10.6 SERV:EFCD <int> [2, 4000] .....................................................................56
3.10.7 SERV:TEMPCO <float> [-4000.0, 4000.0]................................................56
3.10.8 SERV:AGING <float> [-10.0, 10.0] ...........................................................56
3.10.9 SERV:PHASECO <float> [-500.0, 500.0] .................................................57
3.10.10 SERV:1PPS <int> ns [-5000000, 5000000] ............................................57
3.10.11 SERV:TRAC:PORT <RS232 | USB>......................................................57
3.10.12 SERV:TRAC <int> [0,255] ......................................................................57
3.10.13 SERV:EFCS:FAST <float> [0.0, 500.0] ..................................................58
3.10.14 SERV:EFCD:FAST <int> [2, 4000] .........................................................58
3.10.15 SERV:PHASECO:FAST <float> [-500.0, 500.0] .....................................58
3.10.16 SERV? ....................................................................................................59
3.11 CSAC Subsystem........................................................................................ 59
3.11.1 CSAC:RS232? ..........................................................................................60
3.11.2 CSAC:ST? ................................................................................................60
3.11.3 CSAC:STAT?............................................................................................60
3.11.4 CSAC:AL?.................................................................................................60
3.11.5 CSAC:MODE? ..........................................................................................61
3.11.6 CSAC:CONT?...........................................................................................61
3.11.7 CSAC:LAS? ..............................................................................................61
3.11.8 CSAC:TCXO? ...........................................................................................61
3.11.9 CSAC:SIG?...............................................................................................61
3.11.10 CSAC:HEAT? .........................................................................................61
3.11.11 CSAC:TEMP? .........................................................................................61
3.11.12 CSAC:FW? .............................................................................................61
3.11.13 CSAC:SN? ..............................................................................................61
3.11.14 CSAC:LIFE? ...........................................................................................61
3.11.15 CSAC:ST:LAT ONCE .............................................................................62
3.11.16 CSAC:TYPE?..........................................................................................62
3.11.17 CSAC:LOCK? .........................................................................................62
3.11.18 CSAC:POW <ON | OFF>........................................................................62
3.11.19 CSAC? ....................................................................................................62
Chapter 4. Firmware Upgrade Instructions
4.1 Introduction.................................................................................................... 63
4.2 ISP Flash Loader Utility Installation............................................................... 63
4.3 Putting the PCB into In-Circuit Programming (ISP) Mode............................. 63

2020 Microchip Technology Inc. DS50003016A-page 11
4.4 Downloading the Firmware............................................................................ 64
4.4.1 Using the Flash Magic Flash Programming Utility...................................... 64
4.5 Verifying Firmware Update............................................................................ 65
Chapter 5. GPSCon Utility
5.1 Description .................................................................................................... 67
5.2 Installation ..................................................................................................... 67
5.3 Using GPSCon .............................................................................................. 67
5.3.1 Setting the Options..................................................................................... 67
5.3.1.1 Communication Parameters ....................................................... 68
5.3.1.2 Auxillary Parameters .................................................................. 68
5.3.1.3 Traces Parameters ..................................................................... 68
5.3.2 Sending Manual Commands to the Receiver............................................. 70
5.3.3 Using the Mouse in the Graph Window...................................................... 70
5.3.4 Exporting the Graphics............................................................................... 71
5.4 Interpreting the Data...................................................................................... 72
Worldwide Sales and Service .................................................................................... 77

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NOTES:

GPS-2700 USER’S GUIDE
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Chapter 1. Introduction
1.1 OVERVIEW
The GPS-2700, featuring the Chip-Scale Atomic Clock (CSAC), is a game-changing,
disruptive technology culminating from decades of research sponsored by the U.S.
Government. It is a breakthrough technology that allows a Cesium Vapor Cell Atomic
Reference Oscillator to be packaged in a unit several orders of magnitudes smaller
than legacy products, with more than an order of magnitude in power reduction, and
fewer than 2 minutes warm-up to be fully operational, while out-performing many indus-
try-standard Atomic Oscillators.
The CSAC oscillator provides an impressive frequency accuracy, long-term stability,
and fast lock with low power consumption. Through hardware and firmware support,
the GPS-2700 improves the phase noise performance of the unit, and adds an isolated
distribution amplifier with four output channels at 10 MHz. The GPS-2700 provides
LCD, RS-232 and USB serial links for command and control, as well as an aviation bus
compatible power supply that operates from 8V up to 36V with reverse polarity and over
voltage protection, and can thus be directly connected to an aircraft’s 12V or 24V power
bus.
For long term Stratum-1 frequency accuracy and constant calibration the GPS-2700
includes an extremely high-performance GNSS receiver that can acquire and track up
to 72 (50 for uBlox 6 GPS receiver) GNSS signals down to a state of the art
–160dBm, a 32-bit processor that runs a Real Time OS, a low-noise 10 MHz distribu-
tion amplifier with four highly Isolated 10 MHz Sine Wave outputs, one 5 MHz CMOS
output, one 1PPS UTC synchronized CMOS output, RS-232 and USB control inter-
faces, and a generic LCD interface. The GPS-2700 also includes a high-performance
time interval counter that can measure the internally generated 1PPS signal from the
GNSS receiver or an externally supplied 1PPS reference signal with a resolution of 20
picoseconds. The CSAC oscillator is phase-locked to either of these two 1PPS signals
with better than 0.3 ns average phase accuracy typically. Software compensation mea-
sures residual aging, thermal, and g-sensitivity errors of the CSAC oscillator, and
applies electronic compensation to reduce these residual errors. This error compensa-
tion can improve performance especially in GPS-denied environments, and allows
monitoring of the CSAC health and detection of performance abnormalities in the sys-
tem.
Generic NMEA and SCPI (GPIB) commands on two serial interfaces allow very fast
integration into legacy applications, and by using the NMEA serial strings the unit can
behave like a standard GPS receiver albeit with better than 1 meter horizontal accuracy
typically, and full WAAS/EGNOS/MSAS SBAS support.
1.2 OPERATING PRINCIPLES
A Cesium Vapor Cell is excited from a VCEL Laser source. The VCSEL is modulated
at 4.6 GHz to produce a complementary pair of sidebands separated by the cesium
ground state hyperfine frequency of 9.2 GHz. As Cesium supply depletion is not a life-
time limiting factor in the CSAC, the GPS-2700 implementation allows operational life-
times that potentially exceed those of Cesium beam standards by far.

GPS-2700 User’s Guide
DS50003016A-page 14 2020 Microchip Technology Inc.
The Hyperfine transition frequency of the Cesium Vapor cell is affected by adverse
environmental influences, and long-term frequency and phase errors are thus present
in the CSAC. To calibrate these errors out and achieve phase-lock to USNO UTC, the
GPS-2700 uses a GNSS receiver to generate a highly accurate, though unstable 1PPS
signal, and this 1PPS signal is compared with a 1PPS signal generated by the CSAC
10 MHz VCXO. The VCXO is digitally tuned to shift the frequency up or down slightly
and very slowly to keep the CSAC 1PPS reference in phase-lock with the GNSS gen-
erated 1PPS signal. This allows a very close tracking of the U.S. USNO UTC 1PPS sig-
nal to within tens of nanoseconds anywhere in the world, out-performing even the best
free-running Atomic References in the long run. With this software PLL system the
short-term instability of the GNSS receiver is filtered by the CSAC, while the CSAC’s
long-term drift is removed by the GNSS receiver, resulting in both a very good
short-term as well as USNO phase-locked long-term performance.
The 10 MHz VCXO used in the CSAC oscillator exhibits phase noise and numerous
spurs on the output of the CSAC. A dedicated crystal phase noise cleanup oscillator is
phase-locked to the CSAC 10
MHz output with less than 8 Hz loop bandwidth, which
allows the removal of excessive phase noise and spurs from the CSAC output. With
this filter Phase Noise performance is improved typically by 10 dB and more above
8 Hz offset from the carrier, and spur performance is improved significantly. Software
commands allow the cleanup phase noise filter to be switched in and out.
1.3 GENERAL SAFETY PRECAUTIONS
The following general safety precautions must be observed during all phases of oper-
ation of this instrument. Failure to comply with these precautions or with specific warn-
ings elsewhere in this manual violates safety standards of design manufacture, and
intended use of the instrument. Microchip Technology Inc. assumes no liability for the
customer’s failure to comply with these requirements.
1.3.1 Use an Approved Antenna Lightning Protector
The use of an approved, and properly grounded antenna lightning protector on the
GNSS antenna is required to prevent damage, injury or death in case of a lightning
strike.
1.3.2 Grounding
To avoid damaging the sensitive electronic components in the GPS-2700 always make
sure to discharge any built-up electrostatic charge to a good ground source, such as
power supply ground. This should be done before handling the circuit board or anything
connected to it, i.e. the GNSS antenna.
1.3.3 Power Connections
Make sure to connect the DC power to the device following the polarity indicated in
Section 2.4 “Major Connections”.
1.3.4 Environmental Conditions
This instrument is intended for indoor use. The use of a properly installed GNSS
Antenna Lightning Protector is required. It is designed to operate at a maximum relative
non-condensing humidity of 95% and at altitudes of up to 50,000 meters. Refer to the
specifications tables for the DC and AC main voltage requirements and ambient oper-
ating temperature range.

GPS-2700 USER’S GUIDE
2020 Microchip Technology Inc. DS50003016A-page 15
Chapter 2. Quick-Start Instructions
2.1 POWERING UP THE UNIT
The GPS-2700 may be powered from an external 8V to 36V DC source, or simply from
a standard USB port. Both power sources can be connected at the same time. The
internal USB port provides a convenient way to supply power to the unit, as well as
establish serial communications to the unit via a standard USB serial link.
Once serial communications have been established, the user can try sending, and
experimenting with the following useful SCPI commands:
• SYST:STAT?
• GPS?
• SYNC?
• DIAG?
• MEAS?
• CSAC?
• HELP?
2.2 OPERATING THE UNIT FROM A PC’S USB PORT
1. Connect a 5V-compatible GNSS antenna to connector J4.
2. Plug in a short USB cable to USB connector U14. Plug the other end into a stan-
dard USB outlet. Please make sure that the USB cable is no longer than 1 foot
as the IR power drop on longer cables may prevent proper operation of the unit.
No software driver is required when operating under Windows XP/7/8 or later as Win-
dows has the required USB driver already built in. Once installed, the unit should simply
show up as a new Serial Comm Port, and the operator may use Hyperterminal, Ter-
aTerm, GPSCon, or any other serial control software to send commands and query sta-
tus from the unit. The GPSCon software package (see Chapter 5) is recommended for
monitoring and controlling the unit.
The RS-232 serial port on connector J1 operates in parallel to the USB serial port, and
commands can be sent and queried independently to and from both connectors.
English language SCPI (GPIB) commands are available to switch the default serial out-
put of the unit from the RS-232 serial port to the USB port and vice-versa.
2.3 OPERATING THE UNIT FROM THE RS-232 PORT
1. Connect a 5V-compatible GNSS antenna to connector J4.
2. Plug in a clean DC power source of between 8V to 32V (36V max) to the power
pins 15 and 16 of connector J1. Plug in the Ground connection to pins 12 and 14
of connector J1. RS-232 Serial TX and RX signals are available on pins 9 and 8
respectively of connector J1. Make sure not to accidentally short-out adjacent
pins 13 and 15 of connector J1 as this would severely damage the board.

WARNING
Please make sure not to confuse power connector J1 and LCD connector J3 because
these two connectors are mechanically identical and are therefore easy to confuse.
Applying power to LCD connector J3 will severely damage the board.
GPS-2700 User’s Guide
DS50003016A-page 16 2020 Microchip Technology Inc.
The unit will now lock to GPS (Red LED is blinking when satellites are being received)
and will indicate proper lock when the Green LED goes on. Once the green LED is on,
the unit will output 10 MHz and 5 MHz on the outputs with significantly better than 1ppb
frequency accuracy.
Please note that the GNSS receiver establishes the internal antenna-gain right after
power-on, so for proper operation the GNSS antenna should always be connected prior
to turning on the power supply.
2.4 MAJOR CONNECTIONS
The major connections and features of the GPS-2700 PCB are shown in Figure 2-1.
ISP/RESET
LCD Panel
1PPS Out
10MHz Out
5MHz Out
CMOS 5Vpp
LCD PAGE and
GPS Survey Key
USB Communication
and Power
GNSS
Antenna In
8V to 36V Power, RS232
FIGURE 2-1: Major Connections and Features of the GPS-2700.

Quick-Start Instructions
2020 Microchip Technology Inc. DS50003016A-page 17
Table 2-1 shows the functions supported on connector J1.
TABLE 2-1: CONNECTOR J1 PINOUT
Ref Name Function Specification
J1-1 ISP# Enter ISP mode GND pin 1 to activate
J1-2 RST_IN# Reset the instrument GND pin 2 to activate
J1-5 LCD_KEY
Cycle through the LCD
pages. Initiate Auto-Survey.
Wired in parallel with switch
S1.
GND momentarily to cycle
LCD pages. GND for more
than 8 seconds to initiate
Auto-Survey.
J1-7 LOCK_OK_OUT
Indicates that no internal
events are pending, the
hardware is okay, and the
CSAC is locked to GPS.
3.3V CMOS output can drive
up to 5 mA, series-termi-
nated by 33.
J1-8 RX_232 RS-232 receive data RS-232 level
J1-9 TX_232 RS-232 transmit data RS-232 level
J1-10 GPS_RS232
Raw NMEA output from
GNSS receiver in RS-232
level format.
RS-232 level
J1-11 PPS_IN External alternate 1PPS
input
TTL, 3.3V and 5V CMOS
compatible
J1-13 ALARM
Wired in parallel to the Red
LED, blinks whenever a
1PPS pulse is received.
3.3V CMOS level can drive
up to 5 mA, series-termi-
nated by 33.
2.4.1 Harness Pinning
Table 2-2 is a table of the cable harness J1 pinout.
TABLE 2-2: J1 PINOUT
Pin Name
1 ENTER_ISP#
2 RST_IN#
3 GND
4 GND
5 LCD_KEY
6 GND
7 LOCK_OK_OUT
8 RX RS-232
9 TX RS-232
10 GPS_RS232
11 PPS_IN
12 GND
13 ALARM
14 GND
15 +28V
16 +28V

TABLE 2-3: MISCELLANEOUS CONNECTORS
Ref Name Function Specification Pinning
J2 ISP/RESET ISP/RESET jumper GND pin 1 or pin 3 to
activate
J2-1:ISP;
J2-2:GND;
J2-3:RST#
J4 Antenna GNSS Antenna 5V Amplified Antenna,
MMCX connector
Center: RF Input;
Shield: GND
OUT_J1 5MHz OUT 5 MHz output 5V CMOS Center: RF out-
put; Shield: GND
OUT_J2 1PPS OUT 1 pps output 5V CMOS Center: RF out-
put; Shield: GND
OUT_J3-J6 10MHz OUT 10 MHz output Sine wave, +13 dBm
(±3 dBm)
Center: RF out-
put; Shield: GND
GPS-2700 User’s Guide
DS50003016A-page 18 2020 Microchip Technology Inc.
2.4.2 Harness Connectors J1 and J3
The manufacturer for connectors J1 and J3 is Hirose. A mating housing part number
for this connector is available from Digikey and other distributors. Crimp pins are also
available from Digikey for different wire sizes.
The part number of the connectors soldered onto the GPS-2700 PCB is:
Hirose DF11-16DP-2DSA01
2.4.3 Concurrent-GNSS Capabilities
GPS-2700 with firmware revision 0.74 and later and uBlox 8 GNSS receiver is capable
of simultaneously receiving up to three concurrent GNSS systems at one time. Firm-
ware revision 0.74 and later also supports the GPS-2700 with uBlox 6 GPS receiver.
Concurrent GNSS operation aids performance by allowing reception of up to 72 GNSS
satellites in challenged reception areas such as in urban canyons, under foliage,
indoors, or close to the earth's poles, etc. Using multiple GNSS systems also increases
robustness by not relying on a single GNSS system. Several of the systems operate at
different carrier frequencies, so using multiple GNSS systems can increase immunity
against jamming which often occurs at only one carrier frequency.
The multiple GNSS systems each have their own reference time and representation of
UTC. For example, GPS uses the GPS time standard and provides a method to convert
GPS time to UTC as defined by the US Naval Observatory (USNO). GLONASS, Gali-
leo and BeiDou have similar reference times and UTC definitions. The GPS-2700 with
multi-GNSS support automatically adjusts for offsets between the different GNSS time
reference standards and synchronizes the 1PPS output to UTC (USNO) when GPS is
being received. If GPS is not being received, the 1PPS output is synchronized to the
best representation of UTC (USNO) available.
The selection of GNSS systems is made with the GPS:SYST:SEL command as
detailed in Section 3.3.31. Because these systems operate at different carrier frequen-
cies with different bandwidths, it is necessary to use a GNSS antenna that is designed
to receive all the required GNSS systems. Please note that the Galileo system is now
functional, and uses the same carrier frequency as GPS: L1, albeit with a wider band-
width. In our experience Galileo sats can be received with good C/No carrier to noise
figures (>40 dB) with standard legacy GPS antennae and distribution amplifiers/split-
ters. Microchip thus recommends enabling at a minimum GPS, Galileo, and SBAS con-
currently with the command: GPS:SYST:SEL GPS GAL SBAS, see also Section
3.3.31.
Using other GNSS systems such as Glonass will require an antenna system designed
to support Glonass signals.

Quick-Start Instructions
2020 Microchip Technology Inc. DS50003016A-page 19
GPS-2700 with firmware revision 0.75 and later and uBlox 8 GNSS receiver adds bet-
ter support for legacy GPS receiver by switching the main talker ID to $GP for GGA,
Microchip GGA, RMC, and ZDA commands. This command allows the GPS-2700 to
output NMEA sentences with navigation and PVT data for GPS only, see Section
3.3.32 for detailed operations and restrictions on talker ID mode.
The internal GNSS receiver can track up to three different GNSS systems and track up
to 24 satellites concurrently, such as GPS, Galileo, Glonass, and SBAS at the same
time. However only two different carrier frequencies may be received at any given time.
So BeiDou and Glonass cannot be enabled concurrently when either GPS, Galileo,
SBAS, or QZSS are simultaneously enabled as that would require tracking three differ-
ent carrier frequencies.
Attempting to configure an invalid combination of GNSS systems or configure GNSS
systems on GPS-2700 without uBlox 8 receiver with the GPS:SYST:SEL command will
result in a Command Error response with no change to the configuration.
2.4.4 Connecting the GNSS Antenna
Connect the GNSS antenna to connector J4 using the BNC to MMCX cable adapter.
Caution: use a Lightning Arrestor on your Antenna setup. Use an amplified GNSS
antenna that is 5V compatible. The GPS-2700 GNSS (GPS for uBlox 6) receiver is a
72 (50 for uBlox 6 receiver) channel high-sensitivity multi-GNSS receiver with very fast
lock time. The unit can either be used in stationary applications using the automatic
self-survey (Auto Survey with Position Hold) feature, or it can be used in mobile plat-
forms. Using Position Hold mode improves timing and frequency accuracy especially
in GPS-challenged antenna locations such as under foliage or with strong multipath
signals.
The GPS-2700 is capable of generating standard navigation messages (see
GPS:GPGGA, GPS:GPZDA, GPS:GPGSV, GPS:PASHR, and GPS:GPRMC serial
commands) that are compatible with most GPS based navigation software. These nav-
igation messages may either be sent to the RS-232 serial port or to the USB serial port.
The GNSS receiver generates a 1PPS time signal that is phase synchronized to UTC.
This 1PPS signal is used to frequency-lock the 10 MHz Sine-Wave output of the
GPS-2700 to UTC, thus disciplining the unit’s Atomic Clock 10 MHz frequency output
to the US Naval master clock for very high frequency accuracy (typically better than 10
digits of frequency accuracy when locked to GPS). Using a high-performance Timing
GNSS receiver allows operation with a phase stability error of typically less than ±15
nanoseconds anywhere in the world.
2.4.5 Connecting an LCD Display
An optional, industry standard alphanumeric LCD display may be connected to the unit
for displaying status information. LCD's with 16x2 characters are optimal, but 20x2 or
20x4 displays may also work. An example low-cost display is available from
www.mouser.com:
Newhaven Display PN: NHD-0216K1Z-NSW-BBW-L
The connector drives the LCD directly, and the 5V pin can also be used to drive the
LCD's backlighting. Contrast of the LCD is adjusted via software command.
Figure 2-2 shows the mechanical connections. A schematic showing the connections
from the GPS-2700 to the LCD panel is shown in Figure 2-3.

GPS-2700 User’s Guide
DS50003016A-page 20 2020 Microchip Technology Inc.
FIGURE 2-2: LCD Display Connection.
TABLE 2-4: LCD CONNECTOR J3 PINOUT
Pin Name
1 CONTRAST
2 +5V
3 GND
4 LCD_RS
5 For factory use only
6 LCD_RDWR
7 For factory use only
8 LCD_ENABLE
9 For factory use only
10 LCD_DATA4
11 For factory use only
12 LCD_DATA5
13 For factory use only
14 LCD_DATA6
15 For factory use only
16 LCD_DATA7