Microchip Technology Vectron MD-261 Manuale utente

Vectron GNSS Timing Modules

MD-261, MD-171, MD-174

Reference Manual

Rev D, 10-05-18

Vectron GNSS Timing Module Reference Manual, Rev. D, 10-05-18

Vectron • 100 Watts Street • Mount Holly Springs, PA 17065, USA

Revision History

Revision

Date

Description

04/02/2015

•First Release

05/21/2015

•Update for Firmware 4.0

12/13/2016

•Update for Firmware 4.3

10/05/2018

•Update for Firmware 4.4

•Updated section 2.4.3 Reference

Selection

•Updated section 2.3 Operating Modes

 
Vectron GNSS Timing Module Reference Manual, Rev D, 10-05-18 
Vectron • 100 Watts Street • Mount Holly Springs, PA 17065, USA 
3
 
Table of Contents 
CHAPTER 1 INTRODUCTION ...................................................................................................................................... - 4 -
1 INTRODUCTION.................................................................................................................................................. - 4-
2 SCOPE............................................................................................................................................................... - 4-
3 TERMINOLOGY................................................................................................................................................... - 4-
CHAPTER 2 DEVICE OPERATION.............................................................................................................................. - 5 -
1 STARTUP ................................................................................................................................................................. - 5-
2 COMMUNICATIONS................................................................................................................................................... - 5-
3 OPERATION MODES................................................................................................................................................. - 5-
4 MODULE CONFIGURATION ....................................................................................................................................... - 8-
4.1 Output Messages Configuration................................................................................................................... - 8 -
4.2 Module Output Configuration........................................................................................................................ - 8 -
4.3 Reference Selection...................................................................................................................................... - 9 -
4.4 Survey Mode & Position Hold..................................................................................................................... - 11 - 
4.5 Cable Delay.................................................................................................................................................. - 11 - 
4.6 GNSS Fixmask ............................................................................................................................................ - 11 - 
4.7 GNSS System Select.................................................................................................................................. - 12 - 
4.8 GPS Week Rollover .................................................................................................................................... - 12 - 
4.9 Manual Holdover Mode............................................................................................................................... - 13 - 
4.10 Manual Frequency Setting........................................................................................................................ - 13 - 
4.11 Device Reset / Restart.............................................................................................................................. - 13 - 
5 FIRMWARE UPDATES............................................................................................................................................. - 14 -
6 OPERATION MODES &CONDITION REGISTERS...................................................................................................... - 15 -
6.1 Operation Modes......................................................................................................................................... - 15 - 
6.2 Condition Register....................................................................................................................................... - 15 - 
CHAPTER 3 DEVICE INSTALLATION ...................................................................................................................... - 16 - 
1 SERIAL RX AND TXCONNECTIONS........................................................................................................................ - 16 -
2 RECOMMENDED MINIMAL CONNECTIONS............................................................................................................... - 16 -
 
 

Vectron GNSS Timing Module Reference Manual, Rev. D, 10-05-18

Vectron • 100 Watts Street • Mount Holly Springs, PA 17065, USA

Chapter 1

Introduction

1.1 Introduction

The Vectron GNSS Disciplined Oscillator Module is an OEM Micro-Disciplined Oscillator

Module designed to provide a time and frequency reference to systems requiring

synchronization. These modules can be configured to use either GNSS constellations or an

external reference signal, which can be 1PPS (standard) or a reference frequency (contact

factory). This document outlines the available VSIP commands and queries supported by

the module and explains how the commands are used. This document should be used

along with the datasheet and VSIP Reference Manual to properly configure the device.

1.2 Scope

This document currently applies to the MD-171, MD-174, and MD-261 series modules with

firmware versions 4.3 and 4.4.

1.3 Terminology

VSIP

Vectron Serial Interface Protocol

VDOM

Vectron Disciplined Oscillator Module

Device or Target

The VDOM device sending reports and responding to commands

Host

The device, typically a PC, sending commands to the VDOM device; a host may also be

another embedded system, typically communicating with the VDOM device via a UART.

Incoming

From Host to Target

Outgoing

From Target to Host

Permanent Setting

A permanent setting is written to nonvolatile memory and will persist between power

cycles and resets. Permanent settings can be modified by the user any number of times.

Temporary Setting

A temporary setting will only maintain its state during the current runtime, and will revert

to the last permanent setting or factory default upon device power-up or reboot.

Vectron GNSS Timing Module Reference Manual, Rev D, 10-05-18

Vectron • 100 Watts Street • Mount Holly Springs, PA 17065, USA

Chapter 2

Device Operation

2.1 Startup

At startup or after reset the module may take from five to ten seconds to boot up and

begin serial communications. Standard communications startup begins with a

$PVEC,03,VECTRON,init_ok… message indicating that the device successfully loaded and

initialized all settings. If the init_ok field is not given, the device was unable to start due

to a hardware failure or invalid configuration. After the $PVEC,03 message, the first

$PVEC,00 status message will be transmitted in approximately 1.5 seconds. After

transmitting the first status message, the unit will begin processing normal serial

communications. Do not attempt to send any data to the unit before the first status

message is received.

2.2 Communications

The module communicates using an idle high CMOS-level serial UART, transmitting both

VSIP and NMEA talker sentences. The standard port configuration is 115,200 baud, 8 data

bits, no parity, and one stop bit (115200 8N1). Configuration of the device is done using

VSIP commands and queries which are outlined in the section below. See the VSIP

Reference Manual for more information on VSIP commands, queries, and reports. Serial

communication is not required for normal operation; once the device is configured it can

be used as a standalone GPSDO without a host controller.

In standard operating mode, the module will output a status message (VEC,00) every

second. This message indicates the operation mode, DAC value, temperature, uptime, and

other information. Additionally, all supported NMEA messages (see below) can be

configured to be output up to once per second as well. Note: the time fields in GNSS

messages are up to one second ahead of UTC and correspond to the next PPS pulse.

The Vectron VDOM Monitor 3 software application can be used to monitor and configure

the module via the serial interface.

A 3.3 volt USB-to-serial converter, such as the FTDI TTL-232R-3v3, may be used to

connect to the module for configuration and firmware update purposes. Alternatively, the

module can be interfaced with another microcontroller or logic on the customer’s board;

however, it is advisable to allow direct access to the module’s RX and TX pins from a PC

interface (such as the TTL-232R-3v3) to allow for firmware updates using the VDOM

Monitor 3 software. WARNING: DO NOT CONNECT THE CMOS-LEVEL SERIAL PORT TO AN

RS-232 LEVEL SERIAL INTERFACE. THIS WILL DAMAGE THE UNIT.

2.3 Operation Modes

Upon power-up, the module will perform a self-diagnostic test and initialize its internal

registers. This takes approximately ten seconds. After this is completed, VSIP Status

Reports and NMEA 0183 data are transmitted at regular time intervals via the serial TX

Vectron GNSS Timing Module Reference Manual, Rev. D, 10-05-18

Vectron • 100 Watts Street • Mount Holly Springs, PA 17065, USA

pin. The default interval is once per second, but the intervals for all NMEA messages are

configurable. The status information is transmitted using the VEC,00 format. See the VSIP

Protocol document for details of the commands and message format. Errors that occur

during self-diagnostics or any other stages are reported real-time through error messages

and/or the error flag bytes in the status packets.

The disciplined oscillator module has 8 operation modes (opmodes). They are shown in

the flow diagram below. The current mode of operation is included in the serial Status

Report. See the VSIP Protocol document for details.

Figure 2.3a: Operation Modes (opmodes)

Opmode 0 –System Warmup

After the completion of the self-diagnostic test, the module enters the System Warm-up

mode. The duration of this mode after reset or power-on is fixed, but may be from 0 to

1200 seconds. The module may return to this mode momentarily while exiting from a

holdover mode (manual and auto) before re-starting the locking process.

Opmode 1 –Reference Evaluation

In this mode the reference(s) and local oscillator are evaluated for stability. Additionally,

the local 1PPS is coarsely aligned to the reference, if available. The module will remain in

this mode until a suitable reference is detected. If using GNSS constellation(s) as a

reference, the GNSS receiver parameters are evaluated to determine the fitness for use of

the reference.

Opmode 2 –Frequency Locking

Once a suitable reference is detected, a frequency locking routine will begin.

Assuming the reference is determined to be usable, moderate adjustments to the local

oscillator’s frequency are then made to gradually approach nominal. The time spent in this

mode is mostly related to the initial frequency error. Once the local oscillator’s frequency

is within approximately 2ppb or less of nominal, the module will enter Phase Alignment

mode. If the routine is unable to achieve and hold these criteria, the module will return to

reference evaluation.

Opmode 3 –Phase Alignment

Phase alignment is a digital phase adjustment which is intended to bring the local

oscillator within approximately 100ns or better of the reference signal. If the frequency of

both the local oscillator and reference is stable, this mode will exit to opmode 4.

Vectron GNSS Timing Module Reference Manual, Rev D, 10-05-18

Vectron • 100 Watts Street • Mount Holly Springs, PA 17065, USA

Opmode 4 –Phase Locking

In order to maintain synchronization to the reference source, small frequency corrections

to the local oscillator are made. The magnitude of these changes is configurable by the

factory depending on application requirements. These corrections happen at variable

intervals that are related to the stability of the oscillator and/or reference signal. In most

cases, this is the desired steady-state operating mode of the module. Upon entering this

mode after initial reference evaluation, the first (approximately) 5 minutes of this mode

are considered “Coarse Phase Locking” and PPS is not valid. After the stability of the local

oscillator and reference has been established, the PPS is considered valid and the lock bit

(see pinout and VSIP Status Report) will go high, indicating the module is locked to within

its configured threshold. At this point, the module will also enable the output 1PPS and/or

RF if configured to do so (See VEC,12 –Output Configuration).

Opmode 5 –Manual Holdover

The module can be placed into holdover mode at any time using the Holdover Mode Set

command. See the VSIP protocol document for details. This can be used in applications

where the user demands control of when holdover mode is entered, or for testing,

evaluation, or control of module performance. The module will remain in this mode until

the Holdover Mode Set command is issued, with hmode set to 0. The module will then

momentarily return to warmup mode before restarting the normal evaluation and locking

process.

Opmode 6 –Auto Holdover

If the signal is determined to be unusable during phase align or phase locking, the module

will enter auto holdover mode. The more time the module spends in phase locking mode,

the longer it can maintain accuracy during holdover. In Auto Holdover mode, the module

will continually check for the presence and of any reference. If a reference is detected, the

module will transition to either opmode 1, 3, or 4, depending on the phase error of the

local reference compared to the reference at that time.

Vectron GNSS Timing Module Reference Manual, Rev. D, 10-05-18

Vectron • 100 Watts Street • Mount Holly Springs, PA 17065, USA

2.4 Module Configuration

2.4.1 Output Messages Configuration

The module can be configured at runtime to output various GNSS NMEA talker sentences

at user-defined intervals. To configure these messages, use VSIP Command VEC,19

(Configure Messages) at any point during normal device operation. The maximum interval

is 255 seconds, while an interval of 0 disables the message. An ACK indicates that the

given message interval was set correctly.

The module supports the following NMEA outputs, per NMEA standard 0183 (June 2012):

Message ID

Description

GGA

Global Position System Fix Data

GLL

Geographic Position –Latitude/Longitude

GNS

GNSS Fix Data

GSA

GNSS DOP and Active Satellites

GSV

GNSS Satellites in View

RMC

Recommended Minimum Navigation Information

VTG

Course of Ground and Ground Speed

ZDA

Time & Date

The module’s periodic status report message (VEC,00) can also be controlled using

VEC,19. In this case, a message ID of “STATUS” should be used to set the interval of the

VEC,00 report.

By default (after power-up or restart) STATUS, GNS, GSA, and ZDA will be output every

second.

2.4.2 Module Output Configuration

The device can be configured to output both PPS and 10MHz RF in various modes. By

default, the module will output PPS only while locked to a reference (GNSS PPS or an

external PPS) and will always output a 10MHz RF signal. This behavior can be modified

using VSIP Command VEC,12 (Output Select) and can be set either temporarily or

permanently.

VEC,12 controls the PPS Output Source, PPS Output Enable, and RF Output Enable. The

PPS Output can be configured to output the locked PPS (default), the GNSS PPS, or to

pass the external reference PPS (note: there is approximately a 13ns delay through the

module in this case). PPS and RF outputs can be configured to output always, never, or

only when the device is locked to a reference.

Vectron GNSS Timing Module Reference Manual, Rev D, 10-05-18

Vectron • 100 Watts Street • Mount Holly Springs, PA 17065, USA

2.4.3 Reference Selection

The module can lock to either an external reference input or to the internal GNSS

receiver’s PPS. If both references are enabled on the module, the device will use

whichever is available. If both are enabled and available, the device can be configured to

prefer one over the other (GNSS or PPS preferred) or to continuing using the last

reference as long as it is available (No Preference). These settings can be modified using

VSIP Command VEC,10 (Reference Select) and can be set either temporarily or

permanently.

The module is capable of switching from GNSS to and external references in a hitless

fashion; that is, a phase offset will be applied to the external reference so that the

internal timing controls will not see a significant timing shift –allowing the device to stay

locked during the process of switching out of GNSS reference to an external reference,

and back again (assuming the external reference frequency is accurate). Figures 2.2.3a

and 2.2.3b show the reference switching process and holdover exit process, respectively.

Figure 2.4.3a: Reference Switching Process (From Locked Condition)

Vectron GNSS Timing Module Reference Manual, Rev. D, 10-05-18

Vectron • 100 Watts Street • Mount Holly Springs, PA 17065, USA

Figure 2.4.3b: Exit from auto holdover process

For example, if both GNSS and external PPS references are enabled, and GNSS is

preferred, the device will use GNSS whenever it is available. In the event that GNSS

reference is lost (i.e. the antenna is disconnected) the device will attempt to switch to the

external reference. If hitless is disabled and the external reference phase is not closely

aligned with the GNSS PPS, the device must switch to mode 1 (evaluating reference) and

start the locking process from the beginning. If hitless is enabled, the device will apply a

phase offset to the external reference and the lock will not be interrupted. When the

GNSS reference is restored, the device will attempt to switch back to GNSS reference (as

it is preferred in this case). If the phase of the on-board reference (previously locked to

the external reference) is aligned with the GNSS PPS, the device will return to the locking

state. If not aligned, the device will re-start the locking process from mode 1.

Bit 12 of the condition register indicates if a hitless offset is actively being applied to the

external reference input. A ‘1’ in this field indicates there is an offset active. Note that the

hitless offset is only applied to the external reference after switching out of GNSS; it

cannot be used to align the GNSS to the external reference.

Note: It is not shown on the flowchart diagrams, but when switching between aligned

references (with or without an active hitless offset), the module will briefly enter “Auto

Holdover” mode before switching to a new reference. PPS Output will not be affected.

Note: Refsel mode 4 is not supported prior to firmware version 4.5 (selecting this mode

will result in mode 7 operation).

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