Meinberg TCR180, Manual

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6 Functional description of receiver
After the received time code has passed a consistency check, the TCR180’s on-board software clock and battery
buffered real time clock are synchronized according to the external time reference. If an error or inconsistency
is detected in subsequent time code frames, or the input signal is disconnected, the on-board clock switches to
holdover mode, where the time is derived from the on-board high quality oscillator which has been disciplined
before.
All IRIG and similar time codes provide the time-of-day, and a day-of-year number (1...365/366). When con-
verting the day-of-year number from the incoming time code to a calendar date then the result is ambiguous
unless the year number is not known: the day after February 28 can be March 1, but can also be February 29
in case the year is a leap year.
Unfortunately, most of the commonly used IRIG code formats don’t include a year number, in which case
the year number used for the computation of the calendar date is retrieved from the battery buffered on-board
real time clock.
So care must be taken that the on-board clock has been set to the correct date. The on-board date and
time can be adjusted by sending a Meinberg Standard Time string to the serial interface COM0, or via the PCI
bus by using the utility programs included in the driver software package.
If the configured time code format does provide a year number (e.g. IEEE 1344, IEEE C37.118, IRIG-Bxx6/Bxx7)
then the year number from the time code is used instead of the year number from the on-board real time clock,
and the on-board date is set accordingly.
Most of the commonly used IRIG code formats also
don’t provide an indicator whether the transported
time is UTC, or local time with some offset from UTC.
However, the TCR180 always needs to derive UTC time
from the incoming time code since the card’s on-board
time is expected to run on UTC.
If no UTC offset is provided by the time code then a UTC offset parameter on the card first needs to be
configured, depending on the time provided by the input signal. When the TCR180 is shipped then the UTC
parameter is set to "unconfigured", and as long as this is the case the card doesn’t synchronize to the input
signal. So the UTC offset has to be configured first when the card is put into operation. The tools that come
with the driver software package given an appropriate hint if this is the case.
Only if the used time code format provides the UTC offset (e.g. IEEE 1344, IEEE C37.118) the card uses
the UTC offset from the time code, and thus even synchronizes to the input signal if the card’s UTC parameter
is still set to "unconfigured".
Care must be taken, however, if one of the IEEE 1344 or IEEE C37.118 codes is used: The main differ-
ence between these formats is the way the UTC offset is to be applied: subtracted or added. Unfortunately
there are 3rd party IRIG devices out there which claim to use a IEEE 1344 code, but in fact handle the UTC
offset as specified in IEEE C37.118. This may result in a wrong UTC time derived from the time code if local
time is transported. A simple fix is usually to switch the card from one of the IEEE codes to the other one.
10 Date: 4th June 2021 TCR180