Spectracom TSync-PCIe, User Manual

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6.1 Input References
The input references consist of multiple interfaces to various types of Time References. A Time
Reference can take many forms but their fundamental responsibility is they always provide a
1PPS on-time-point, they usually provide a time-of-day and date input and they might provide a
control and status protocol to the time source. The input references can also provide other time
related data such as Leap Second indication and number of seconds, Julian date, day of year,
day of week, week of year, status, sync indication, accuracy indication and other fields unre
lated to time.
The TSync-PCIe architecture’s input reference subsystem is designed to support multiple possible
input references, while allowing only a single time reference and 1PPS reference to discipline
the local clock subsystem at any given time. The user can choose to use the factory default pri
ority list for input references, or may define a proprietary priority list. This user priority list can
be created to combine different time and 1PPS sources (such as GNSS time coupled with the
external 1PPS). The user is also provided with the means to enable or disable the selection of a
specified input reference allowing them to disregard the list and synchronize to a specific out
put.
6.1.1 GNSS Receivers as Input References
GNSS receivers are usually the highest precision and accuracy time references a TSync-PCIe
board can select. GNSS receivers use coaxial GNSS antenna input and typically provides a
serial interface and a 1PPS output. The serial interface can be used for bi-directional com
munication with the GNSS receiver to implement a control and status protocol which conveys
time and position information.
6.1.2 IRIG Inputs
Inter-range instrumentation group time codes, more commonly referred to as “IRIG” time codes,
were created by the Tele-Communications Working Group of the Inter-Range Instrumentation
Group, which is a standard body formed by Range Commanders Council. This standard was
used by US Government military test ranges, NASA, and other research organizations to dis
tribute telemetry information, including time and frequency. The current standard version is IRIG
Standard 200-4. The TSync-PCIe architecture uses IRIG formats as both input and output ref
erences. IRIG formats can be amplitude modulated, or they can be digital signals at various car
rier and clock rates.
The TSync-PCIe architecture supports IRIG inputs with Formats A, B, and G. It supports inputs
and outputs using modulation frequency values of pulse width code, also known as DCLS (0),
and sine wave amplitude modulated coding. Additionally, the board supports inputs with fre
quency/resolution values of no carrier/index count interval, 1 kHz/1 ms, 10 kHz/0.1 ms, and
100 kHz/10 ms, as well as IRIG input coded expressions of the fields BCDTOY, CF, SBS, and
BCDYEAR.
The TSync-PCIe board supports IRIG inputs of the following coded expressions combinations for
BCDTOY, CF, SBS, and BCDYEAR fields:
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Instruction Manual XYZ Rev. R
6.1 Input References