Jackson Labs FireFly-1A GPSDO User manual

FireFly-1A User
Manual
Document: 80200501
Version: 1.2
Date: 6 July, 2011

FireFly-1A User Manual
Copyright © 2010, 2011 Jackson Labs Technologies, Inc.

© 2011 Jackson Labs Technologies, Inc. i
FireFly-1A User Manual
1 Introduction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1
1.1 Overview . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1
1.2 General Safety Precautions . . . . . . . . . . . . . . . . . . . . . . . . 1
1.2.1 Grounding . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1
1.2.2 Power Connections. . . . . . . . . . . . . . . . . . . . . . . . . 1
1.2.3 Environmental Conditions . . . . . . . . . . . . . . . . . . . . . . 1
2 Quick-Start Instructions . . . . . . . . . . . . . . . . . . . . . . 3
2.1 Powering Up the Unit . . . . . . . . . . . . . . . . . . . . . . . . . . 3
2.1.1 Major connections . . . . . . . . . . . . . . . . . . . . . . . . . 3
2.2 Coaxial Connector types . . . . . . . . . . . . . . . . . . . . . . . . . 4
2.3 Connecting the GPS Antenna . . . . . . . . . . . . . . . . . . . . . . . 4
2.4 Remote serial control . . . . . . . . . . . . . . . . . . . . . . . . . . 5
2.4.1 “Help” and command overview . . . . . . . . . . . . . . . . . . . . 5
2.4.2 Loop parameter adjustment . . . . . . . . . . . . . . . . . . . . . 5
3 SCPI-Control Quick Start Instructions . . . . . . . . . . . . . . 7
3.1 Introduction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 7
3.2 General SCPI Commands . . . . . . . . . . . . . . . . . . . . . . . . 7
3.2.1 *IDN? . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 7
3.2.2 HELP?. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 7
3.3 GPS Subsystem . . . . . . . . . . . . . . . . . . . . . . . . . . . . 7
3.3.1 GPS:SATellite. . . . . . . . . . . . . . . . . . . . . . . . . . . 8
3.3.2 GPS:SATellite:TRAcking:COUNt? . . . . . . . . . . . . . . . . . . . 8
3.3.3 GPS:SATellite:VISible:COUNt? . . . . . . . . . . . . . . . . . . . . 8
3.3.4 NMEA Support . . . . . . . . . . . . . . . . . . . . . . . . . . 8
3.3.5 GPS:GPGGA . . . . . . . . . . . . . . . . . . . . . . . . . . . 9
3.3.6 GPS:GGASTat . . . . . . . . . . . . . . . . . . . . . . . . . . 9
3.3.7 GPS:GPRMC . . . . . . . . . . . . . . . . . . . . . . . . . . . 9
3.3.8 GPS:XYZSPeed . . . . . . . . . . . . . . . . . . . . . . . . . . 9
3.3.9 GPS:POSition? . . . . . . . . . . . . . . . . . . . . . . . . . .10
3.3.10GPS:RESET ONCE . . . . . . . . . . . . . . . . . . . . . . . .10
3.3.11GPS? . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .10
3.4 PTIME Subsystem . . . . . . . . . . . . . . . . . . . . . . . . . . .10
3.4.1 PTIMe:TZONe? . . . . . . . . . . . . . . . . . . . . . . . . . .10
3.4.2 PTIMe:DATE?. . . . . . . . . . . . . . . . . . . . . . . . . . .10
3.4.3 PTIMe:TIME? . . . . . . . . . . . . . . . . . . . . . . . . . . .11
3.4.4 PTIMe:TIME:STRing?. . . . . . . . . . . . . . . . . . . . . . . .11
3.4.5 PTIMe:TINTerval? . . . . . . . . . . . . . . . . . . . . . . . . .11
3.4.6 PTIME? . . . . . . . . . . . . . . . . . . . . . . . . . . . . .11
3.5 SYNChronization Subsystem . . . . . . . . . . . . . . . . . . . . . . .11
3.5.1 SYNChronization:SOURce:MODE [GPS|EXTernal|AUTO] . . . . . . . . .11
3.5.2 SYNChronization:HOLDover:DURation? . . . . . . . . . . . . . . . .12
3.5.3 SYNChronization:HOLDover:INITiate. . . . . . . . . . . . . . . . . .12
3.5.4 SYNChronization:HOLDover:RECovery:INITiate . . . . . . . . . . . . .12
3.5.5 SYNChronization:TINTerval? . . . . . . . . . . . . . . . . . . . . .12
3.5.6 SYNChronization:IMMEdiate . . . . . . . . . . . . . . . . . . . . .12
3.5.7 SYNChronization:FEEstimate? . . . . . . . . . . . . . . . . . . . .12
3.5.8 SYNChronization:LOCKed? . . . . . . . . . . . . . . . . . . . . .13
3.5.9 SYNChronization:health? . . . . . . . . . . . . . . . . . . . . . .13

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3.5.10SYNChronization?. . . . . . . . . . . . . . . . . . . . . . . . . 14
3.6 DIAGnostic Subsystem . . . . . . . . . . . . . . . . . . . . . . . . . 14
3.6.1 DIAGnostic:ROSCillator:EFControl:RELative? . . . . . . . . . . . . . . 14
3.6.2 DIAGnostic:ROSCillator:EFControl:ABSolute?. . . . . . . . . . . . . . 14
3.7 MEASURE Subsystem . . . . . . . . . . . . . . . . . . . . . . . . . 14
3.7.1 MEASure:VOLTage?. . . . . . . . . . . . . . . . . . . . . . . . 14
3.7.2 MEASure:CURRent?. . . . . . . . . . . . . . . . . . . . . . . . 15
3.7.3 MEASure?. . . . . . . . . . . . . . . . . . . . . . . . . . . . 15
3.8 SYSTEM Subsystem . . . . . . . . . . . . . . . . . . . . . . . . . . 15
3.8.1 SYSTem:COMMunicate . . . . . . . . . . . . . . . . . . . . . . 15
3.8.1.1 SYSTem:COMMunicate:SERial:ECHO . . . . . . . . . . . . . 15
3.8.1.2 SYSTem:COMMunicate:SERial:PROmpt . . . . . . . . . . . . 15
3.8.1.3 SYSTem:COMMunicate:SERial:BAUD . . . . . . . . . . . . . 15
3.8.2 SYSTem:STATus? . . . . . . . . . . . . . . . . . . . . . . . . 16
3.8.3 SYSTem:FACToryReset ONCE . . . . . . . . . . . . . . . . . . . 16
3.9 SERVO Subsystem. . . . . . . . . . . . . . . . . . . . . . . . . . . 16
3.9.1 SERVo:COARSeDac . . . . . . . . . . . . . . . . . . . . . . . 16
3.9.2 SERVo:DACGain . . . . . . . . . . . . . . . . . . . . . . . . . 16
3.9.3 SERVo: EFCScale . . . . . . . . . . . . . . . . . . . . . . . . 16
3.9.4 SERVo:EFCDamping . . . . . . . . . . . . . . . . . . . . . . . 17
3.9.5 SERVo:SLOPe . . . . . . . . . . . . . . . . . . . . . . . . . . 17
3.9.6 SERVo:TEMPCOmpensation . . . . . . . . . . . . . . . . . . . . 17
3.9.7 SERVo:AGINGcompensation . . . . . . . . . . . . . . . . . . . . 17
3.9.8 SERVo:PHASECOrrection . . . . . . . . . . . . . . . . . . . . . 17
3.9.9 SERVo:1PPSoffset . . . . . . . . . . . . . . . . . . . . . . . . 17
3.9.10SERVo:TRACe . . . . . . . . . . . . . . . . . . . . . . . . . . 18
3.9.11SERVo? . . . . . . . . . . . . . . . . . . . . . . . . . . . . 18
4 Firmware Upgrade Instructions . . . . . . . . . . . . . . . . . 21
4.1 Introduction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 21
4.2 ISP Flash Loader Utility installation. . . . . . . . . . . . . . . . . . . . . 21
4.2.1 Philips LPC2000 Flash Utility . . . . . . . . . . . . . . . . . . . . 21
4.2.2 Flash Magic Flash Programming Utility. . . . . . . . . . . . . . . . . 21
4.3 Putting the PCB into In-Circuit Programming (ISP) mode . . . . . . . . . . . . 22
4.4 Downloading the firmware . . . . . . . . . . . . . . . . . . . . . . . . 22
4.4.1 Philips LPC2000 Flash Utility . . . . . . . . . . . . . . . . . . . . 22
4.4.2 Flash Magic Flash Programming Utility. . . . . . . . . . . . . . . . . 24
4.5 Verifying Firmware Update . . . . . . . . . . . . . . . . . . . . . . . . 27
5 GPSCon Utility . . . . . . . . . . . . . . . . . . . . . . . . . . . 29
5.1 Description . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 29
5.2 Installation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 29
5.3 Using GPSCon . . . . . . . . . . . . . . . . . . . . . . . . . . . . 29
5.3.1 Setting the options. . . . . . . . . . . . . . . . . . . . . . . . . 29
5.3.1.1 Communication Parameters. . . . . . . . . . . . . . . . . . 30
5.3.1.2 Auxiliary parameters. . . . . . . . . . . . . . . . . . . . . 30
5.3.1.3 Other options . . . . . . . . . . . . . . . . . . . . . . . 32
5.3.2 Sending manual commands to the receiver . . . . . . . . . . . . . . . 32
5.3.3 Use of the mouse in graph mode . . . . . . . . . . . . . . . . . . . 33
5.3.4 Exporting the graphics . . . . . . . . . . . . . . . . . . . . . . . 35
5.4 Interpreting the Data . . . . . . . . . . . . . . . . . . . . . . . . . . 36

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6 Certification and Warranty. . . . . . . . . . . . . . . . . . . . .37
6.1 Certification . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .37
6.1.1 Warranty . . . . . . . . . . . . . . . . . . . . . . . . . . . . .37
6.1.2 Limitation of Warranty. . . . . . . . . . . . . . . . . . . . . . . .37
6.1.3 Exclusive Remedies . . . . . . . . . . . . . . . . . . . . . . . .38

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FireFly-1A User Manual
1Introduction
1.1 Overview
The FireFly-1A GPSDO includes an extremely high-performance GPS receiver that can acquire and
track up to 50 GPS signals down to a state of the art –160dBm, a 32bit processor that runs a Real
Time OS, a low-noise sine wave 10MHz output, 1PPS UTC synchronized output, RS-232 control
interface, precision voltage references, and DACs.
1.2 General Safety Precautions
The following general safety precautions must be observed during all phases of operation of this
instrument. Failure to comply with these precautions or with specific warnings elsewhere in this
manual violates safety standards of design manufacture, and intended use of the instrument. Jackson
Labs Technologies, Inc. assumes no liability for the customer’s failure to comply with these
requirements.
1.2.1 Grounding
To avoid damaging the sensitive electronic components in the FireFly-1A GSPDO 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 GPS
antenna.
1.2.2 Power Connections
Make sure to connect the DC power to the device following the polarity indicated in Section 2.1 . Do
not reverse the power pins as this will cause serious damage to the circuit board.
1.2.3 Environmental Conditions
This instrument is intended for indoor use. It is designed to operate at a maximum relative
non-condensing humidity of 95% and at altitudes of up to 4000 meters. Refer to the specifications
tables for the ac mains voltage requirements and ambient operating temperature range.

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2Quick-Start
Instructions
2.1 Powering Up the Unit
The unit is powered from a 8V - 14V DC source. The current is typically less than 0.15A at 12V.
Connect a clean +12V power supply to J5. The connector style is a MolexPart Number 22-23-2031
connector.
Warning: Do not reverse the polarity of the power connector, this will damage the unit.
2.1.1 Major connections
The major connections and features of the FireFly-1A PCB are shown in :Figure 2.1.
Figure 2.1 Major connections to FireFly-1A
GPS
Antenna
+12V
GND 10MHz
1PPS
RS-232 RX
RS-232 TX
GND
LOCK
OK
,
ISP

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Table 2.1 shows the FireFly-1A revision 2.0 hardware connectors
Table 2.1 FireFly-1A hardware connectors
2.2 Coaxial Connector types
There are three coaxial connectors on the FireFly-1A board. They are the following types:
J1, antenna: MMCX
J3, 1PPS output: SMB
J4, 10MHz sine output: SMB
2.3 Connecting the GPS Antenna
Connect the GPS antenna to the BNC to MMCX cable adapter. Caution: use a Lightning Arrestor on
your Antenna setup. Use an amplified GPS antenna that is 3V LNA compatible. The FireFly-1A GPS
receiver is a 50 channel high-sensitivity GPS receiver with very fast lock time. It does not require any
self-survey or position-hold mode (auto survey), and thus can be used in mobile platforms.
FireFly-1A is capable of generating standard navigation messages (see GPS:GPGGA and
GPS:GPRMC RS-232 commands) that are compatible with most GPS based navigation software.
Please note that FireFly-1A indicates MSL height (rather than GPS height) in its GPGGA, GPS? and
syst:stat? output strings.
The GPS receiver generates a 1PPS time signal that is phase synchronized to UTC. This 1PPS signal
is used to frequency-lock the 10MHz Sine-Wave output of the FireFly-1A GPSDO to UTC, thus
disciplining the unit’s 10MHz frequency output to the US Naval master clock for very high
frequency accuracy (typically better than 1ppb offrequency accuracy when locked to GPS). Over the
long term, the FireFly-1A will out-perform free-running Cesium Atomic Frequency Standards.
Ref Name Function
Specification
Pinning
J5 +12V Clean +12V Supply 8.0V-14.0V DC, <0.5A, <10mVac 3 +12V, 2-GND, 1-GND
J4 Sine Out 10MHz Output +11dBm +/-3dB 10MHz Output Center-Sine Output, Shield-GND
J3 1PPS Out 1PPS Output 3.3V CMOS, Rising Edge
Synchronized Center-1PPS Output, Shield-GND
J6 RS-232 RS-232
Communication 115Kbaud, 8N1, RS-232 3-RX, 2-GND, 1-TX
J1 Antenna GPS Antenna 3.0V Amplified Antenna MMCX
connector Center-RF Input, Shield-GND
J2 ISP/Status Alarm/Lock Status
indicators, and
Enable-ISP Flash
Download Mode
Pin 3: 3.3V CMOS output
Pin 2: 4.7Kohm pull-up on open
collector to 3.3V
3-LOCK-OK indicator, can drive an
LED
2-ALARM (unlock) indicator, needs
buffering
1-GND
[Connect pin 2 to ground during
power-on to enter ISP
flash-firmware-download mode]

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2.4 Remote serial control
• The unit is controlled via the Serial port at 115200 baud, 8N1. Other Baud Rates can be set via
SCPI commands.
• Connect the RX, TX, and GND pins of connector J6 to a standard RS-232 connector, attaching the
FireFly-1A unit to your PC’s Hyperterminal, or the optional GPSCon software package. An
RS-232 level shifter is built into the FireFly-1A PCB. A free control/graphing program for
Windows called Z38XX is available on the Jackson Labs Technologies, Inc. website under the
“support” tab.
2.4.1 “Help” and command overview
• A listing of the available RS-232 commands can be shown by typing "help?".
• "*IDN?" can be used to see if the connection works. Both commands need to be followed by
pressing “Enter”.
2.4.2 Loop parameter adjustment
• All loop parameters can be controlled via the RS-232 serial port.
• Loop parameters are optimized for the OCXO on the board, and changing the factory settings may
result in the unit’s performance to deteriorate.
The commands to control the loop parameters are part of the servo? command. See also the SERVO
Subsystem section below.
The individual commands are:
EFC Scale: this is the proportional gain of the PID loop. Higher values will give quicker
convergence, and faster locking of the GPS time (lower loop time constant), lower values give less
noise. Values between 0.7 and 6.0 are typical.
EFC Damping: overall IIR filter time constant. Higher values increase loop time constant. Jackson
Labs Technologies, Inc. typically uses values between 10 to 50. Setting this value toohigh may cause
loop instability.
Phase compensation: this is the Integral part of the PID loop. This corrects phase offsets between the
FireFly-1A 1PPS signal and the UTC 1PPS signal as generated by the GPS receiver. Set higher
values for tighter phase-following at the expense of frequency stability. Typical values range from 4
- 30, 25 being the default. Setting this value too high may cause loop instability.
A well-compensated unit will show performance similar to the plot in Figure 2.2 when experiencing
small perturbations

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Figure 2.2 FireFly-1A phase compensation plot

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3SCPI-Control Quick
Start Instructions
3.1 Introduction
The SCPI (Standard Commands for Programmable Instrumentation) subsystem is accessed via the
RS-232 interface and a terminal program. By default the terminal settings are 115200, 8N1.
There are a number of commands that can be used as listed below. Most of these are identical or
similar to Symmetricom 58503A commands.To get a listing of the available commands, send the
HELP? query. This will return a list of all the available commands for the FireFly-1A GPSDO.
Additional information regarding the SCPI protocol syntax can be found on the following web site:
http://www.scpiconsortium.org
Please refer to the document SCPI-99.pdf for details regarding individual SCPI command
definitions. A basic familiarity with the SCPI protocol is recommended when reading this chapter.
3.2 General SCPI Commands
3.2.1 *IDN?
This query outputs an identifying string. The response will show the following information:
<company name>, <model number>, <serial number>, <firmware revision>
3.2.2 HELP?
This query returns a list of the commands available for the FireFly GPSDO.
3.3 GPS Subsystem
Note: Please note that FireFly-1A displays antenna height in MSL Meters rather than in GPS Meters
on all commands that return antenna height [the legacy Fury GPSDO uses GPS height].

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The GPS subsystem regroups all the commands related to the control and status of the GPS receiver.
The list of the commands supported is the following :
GPS:SATellite:TRAcking:COUNt?
GPS:SATellite:VISible:COUNt?
GPS:GPGGA <int> [0,255]
GPS:GGASTat <int> [0,255]
GPS:GPRMC <int> [0,255]
GPS:XYZSPeed <int> [0,255]
GPS:POSition?
GPS:RESET ONCE
GPS
3.3.1 GPS:SATellite
This group of commands describe the satellite constellation.
3.3.2 GPS:SATellite:TRAcking:COUNt?
This query returns the number of satellites being tracked.
3.3.3 GPS:SATellite:VISible:COUNt?
This query returns the number of satellites (PRN) that the almanac predicts should be visible, given
date, time, and position.
3.3.4 NMEA Support
The following two commands allow the FireFly-1A GPSDO to be used as an industry standard
navigation GPS receiver. The GPGGA and GPRMC NMEA commands comprise all necessary
information about the antenna position, height, velocity, direction, satellite info, fix info, time, date
and other information that can be used by standard navigation applications via the FireFly-1A
RS-232 interface.
Once enabled, FireFly-1A will send out information on the RS-232 transmit pin automatically every
N seconds. All incoming RS-232 commands are still recognized by FireFly-1A since the RS-232
interface transmit and receive lines are completely independent of one another.
Please note that the position, direction, and speed data is delayed by one second from when the GPS
receiver internally reported these to the FireFly-1A Microprocessor, so the position is valid for the
1PPS pulse previous to the last 1PPS pulse at the time the data is sent (one second delay). The time
and date are properly output with correct UTC synchronization to the 1PPS pulse immediately prior
to the data being sent.

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Once set, the following two commands will be stored in NV memory, and generate output
information even after power to the unit has been cycled.
3.3.5 GPS:GPGGA
This command instructs the FireFly-1A to send the NMEA standard string $GPGGA every N
seconds, with N in the interval [0,255]. The command is disabled during the initial 4 minute OCXO
warmup phase.
This command has the following format:
GPS:GPGGA <int> [0,255]
GPGGA shows height in MSL Meters, this is different from traditional GPS receivers that display
height in GPS Meters. The difference between MSL and GPS height can be significant, 35m or more
are common.
3.3.6 GPS:GGASTat
This command instructs the FireFly-1A to send a modified version of the NMEA standard string
$GPGGA every N seconds, with N in the interval [0,255]. The command is disabled during the initial
7 minute OCXO warmup phase.
This command has the following format:
GPS:GGASTat <int> [0,255]
This command replaces the regular NMEA GGA validity flag with a decimal number indicating the
lock-state of the unit. Please see section SERVo:TRACe for a detailed description of the lock state
variable. The command allows capture of the position and other information available in the GGA
command, as well as tracking the lock state and health of the unit’s OCXO performance.
GGASTat shows height in MSL Meters, this is different from traditional GPS receivers that display
height in GPS Meters. The difference between MSL and GPS height can be significant, 35m or more
are common.
3.3.7 GPS:GPRMC
This command instructs the FireFly-1A to send the NMEA standard string $GPRMC every N
seconds, with N in the interval [0,255]. The command is disabled during the initial 4 minute OCXO
warmup phase.
This command has the following format:
GPS:GPRMC <int> [0,255]
3.3.8 GPS:XYZSPeed
Firmware version 0.909 and later add a 3D velocity vector output command. Enabling this command
will output a 3 dimensional velocity vector indicating the unit’s speed in centimeters per second as
well as the Time Of Week in milliseconds.
X, Y, and Z speed are individually given, and are independent of each other. An accuracy estimate in
centimeters per second is also given. The velocity data is time-stamped using the time-of-week with

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a resolution of milliseconds. Use the following format to generate the velocity vector every N
seconds, with N in the interval [0,255]:
GPS:XYZSPeed <int> [0,255]
3.3.9 GPS:POSition?
This command will return the position and height of the GPS antenna, including velocity and track
over ground.
3.3.10 GPS:RESET ONCE
This command will re-initialize the GPS receiver.
3.3.11 GPS?
This query displays the configuration, position, speed, height and other relevant data of the GPS
receiver in one convenient location.
3.4 PTIME Subsystem
The PTIME subsystem regroups all the commands related to the management of the time.The list of
the commands supported is the following :
PTIMe:TZONe?
PTIMe:DATE?
PTIMe:TIME?
PTIMe:TIME:STRing?
PTIMe:TINTerval?
PTIME?
3.4.1 PTIMe:TZONe?
Returns the local time zone offset.
3.4.2 PTIMe:DATE?
This query returns the current calendar date. The local calendar date is referenced to UTC time. The
year, month, and day are returned.

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3.4.3 PTIMe:TIME?
This query returns the current 24-hour time. The local time is referenced to UTC time. The hour,
minute, and second is returned.
3.4.4 PTIMe:TIME:STRing?
This query returns the current 24-hour time suitable for display (for example, 13:24:56).
3.4.5 PTIMe:TINTerval?
This query is equivalent to the command SYNChronization:TINTerval
3.4.6 PTIME?
This query returns at once the result of the four following queries:
PTIME:DATE?
PTIME:TIME?
PTIME:TZONE?
PTIME:TINTerval?
3.5 SYNChronization Subsystem
This subsystem regroups the commands related to the synchronization of the FireFly-1A with the
GPS receiver. The list of the commands supported for this subsystem is the following:
SYNChronization:SOURce:MODE [GPS|EXTernal|AUTO]
SYNChronization:SOURce:STATE?
SYNChronization:HOLDover:DURation?
SYNChronization:HOLDover:INITiate
SYNChronization:HOLDover:RECovery:INITiate
SYNChronization:TINTerval?
SYNChronization:IMMEdiate
SYNChronization:FEEstimate?
SYNChronization:LOCKed?
SYNChronization?
3.5.1 SYNChronization:SOURce:MODE [GPS|EXTernal|AUTO]
The board may be configured lock to an external 1PPS source, or the internal GPS receiver. A small
through-hole pad next to the SMA connectors labeled “1PPS IN” may be used to feed an external
CMOS rising-edge 1PPS signal with 0V < x <5V signal level, and 1us minimum pulse width into the
unit. Use one of the various ground pins on the board as a 1PPS signal return.

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12 © 2011 Jackson Labs Technologies, Inc.
By default the unit is set to GPS. It may be hard-coded to only use the external 1PPS source by
setting EXT, or it may be auto-switched to the external 1PPS signal if the internal GPS receiver does
not generate 1PPS pulses for longer than 15 seconds if the signal is too week, or there is a GPS
failure. When set to the AUTO setting, the unit will switch back to the internal GPS receiver once
1PPS pulses are generated internally again.
3.5.2 SYNChronization:HOLDover:DURation?
This query returns the duration of the present or most recent period of operation in the holdover and
holdover processes. This is the length of time the reference oscillator was not locked to GPS. The
time units are seconds. The first number in the response is the holdover duration. The duration units
are seconds, and the resolution is 1 second. If the Receiver is in holdover, the response quantifies the
current holdover duration. If the Receiver is not in holdover, the response quantifies the previous
holdover. The second number in the response identifies the holdover state. A value of 0 indicates the
Receiver is not in holdover; a value of 1 indicates the Receiver is in holdover.
3.5.3 SYNChronization:HOLDover:INITiate
The command will place the unit into a forced holdover state, while still indicating the difference
between the internal 1PPS generated by the OCXO and the GPS generated 1PPS. This command is
useful to measure the OCXO drift when in holdover. Please note that the Time Interval Counter is
limited to +/-2000ns display range. The time interval difference may be displayed with the SYNC?
command.
3.5.4 SYNChronization:HOLDover:RECovery:INITiate
This command terminates a manual holdover that was initiated with the SYNC:HOLD:INIT
command, and return the unit to normal GPS locking mode.
3.5.5 SYNChronization:TINTerval?
This query returns the difference or timing shift between the FireFly-1A 1 PPS and the GPS 1 PPS
signals. The resolution is 1E-10 seconds.
3.5.6 SYNChronization:IMMEdiate
This commandinitiates a near-instantaneous alignmentof the GPS 1 PPS and Receiver output 1 PPS.
To be effective, this command has to be issued while not in holdover.
3.5.7 SYNChronization:FEEstimate?
This query returns the Frequency Error Estimate, similar to the Allan Variance using a 1000s
measurement interval and comparing the internal 1PPS to GPS 1PPS offset.
Values less than 1E-012 are below the noise floor, and are not significant.

© 2011 Jackson Labs Technologies, Inc. 13
FireFly-1A User Manual
3.5.8 SYNChronization:LOCKed?
This query returns the lock state (0=OFF, 1=ON) of the PLL controlling the OCXO.
3.5.9 SYNChronization:health?
The SYNChronization:health? query returns a hexadecimal number indicating the system’s
health-status.. Error flags are encoded in a binary fashion so that each flag occupies one single bit of
the binary equivalent of the hexadecimal health-status flag.
The following system parameters are monitored and indicated through the health-status indicator.
Individual parameters are ‘ored’ together which results in a single hexadecimal value encoding the
following system status information:
As an example, if the unit is in GPS holdover, and the OCXO voltage is too high, and the UTC phase
offset is > 250ns then the following errors would be indicated:
1) UTC phase > 250ns: 0x4
2) OCXO voltage too high: 0x40
3) GPS in holdover: 0x10
‘Oring’ these values together results in:
0x40 | 0x10 | 0x4 = 0x54
The unit would thus indicate: HEALTH STATUS: 0x54
A health status of 0x0 indicates a properly locked, and warmed-up unit that is completely healthy.
If the OCXO coarse-DAC is maxed-out at 255 HEALTH STATUS |= 0x1;
If the OCXO coarse-DAC is mined-out at 0 HEALTH STATUS |= 0x2;
If the phase offset to UTC is >250ns HEALTH STATUS |= 0x4;
If the run-time is < 300 seconds HEALTH STATUS |= 0x8;
If the GPS is in holdover > 60s HEALTH STATUS |= 0x10;
If the Frequency Estimate is out of bounds HEALTH STATUS |= 0x20;
If the OCXO voltage is too high HEALTH STATUS |= 0x40;
If the OCXO voltage is too low HEALTH STATUS |= 0x80;
If the short-term-drift (ADEV @ 100s) > 100ns HEALTH STATUS |= 0x100;
For the first 7 minutes after a phase-reset, or a coarsedac change: HEALTH STATUS |= 0x200;

FireFly-1A User Manual
14 © 2011 Jackson Labs Technologies, Inc.
3.5.10 SYNChronization?
This query returns the results of these six queries :
SYNChronization:SOURce:MODE?
SYNChronization:SOURce:STATE?
SYNChronization:LOCKed?
SYNChronization:HOLDover:DURation?
SYNChronization:FEEstimate?
SYNChronization:TINTerval?
SYNChronization:health?
3.6 DIAGnostic Subsystem
This subsystem regroups the queries related to the diagnostic of the OCXO.The list of the commands
supported for this subsystem is as follows:
DIAGnostic:ROSCillator:EFControl:RELative?
DIAGnostic:ROSCillator:EFControl:ABSolute?
3.6.1 DIAGnostic:ROSCillator:EFControl:RELative?
This query returns the Electronic Frequency Control (EFC) output value of the internal reference
oscillator. It returns a percentage value between -100% to +100%. :
3.6.2 DIAGnostic:ROSCillator:EFControl:ABSolute?
This query returns the Electronic Frequency Control (EFC) output value of the internal reference
oscillator. It returns a value in volts between 0 and 5 V
3.7 MEASURE Subsystem
This subsystem regroups the queries related of some parameters that are measured on-board on the
FireFly-1A. The list of the commands supported for this subsystem is the following:
MEASure:VOLTage?
MEASure:CURRent?
MEASure?
3.7.1 MEASure:VOLTage?
This command is not supported in FireFly-1A, and will return undetermined values.