Auto Tc Reader Operations; Ltc Generator Operations - AEC PCIe-TC User Manual

AUTO TC READER OPERATIONS

Many PCIe-TC board models are capable of reading both LTC and VITC
simultaneously. The PCIe-VLTC/RDA board is a good example.
Normally it is assumed that the LTC data and VITC data match each
other on a frame by frame basis at play speed. Whenever it is in "Auto
LTC/VITC Reader Mode", the PCIe-TC board automatically selects either
LTC data or VITC data to be placed into the "selected reader" area of its
memory. This data area, which is exactly the same data area used by the
LTC reader mode and the VITC reader mode, can then be easily read by
application programs in the usual manner.
The type of time code (LTC vs. VITC) which is currently "selected" is that
which "looks best" to the board's hardware and software. If the board is
currently using LTC data, then that data disappears, the board will switch
over to reading VITC data within a fraction of a second. If neither LTC
nor VITC data is present, the board will continuously switch back and
forth between the two choices until it finds a valid time code signal again.
When installed inside a computer running Microsoft Windows, the best
way to see how the "Auto LTC/VITC Reader Mode" works is to use the
Windows demo application included on the PCIe-TC test/demo/support
CDROM. A little status box tells you whether LTC or VITC data is cur-
rently selected. You can alternately disconnect and reconnect the LTC
and VITC cables (or leave both disconnected temporarily) and see how
the board responds. The algorithm used by the PCIe-TC board was cho-
sen to work well in most situations. Your application may require some-
thing a little bit different, in which case you will have to write or use some
custom software to achieve the desired result.
There are some applications where the LTC data and VITC data contain
two completely different sets of time code information. The board can
handle this with no problem, but you will have to write or use custom
software which tells the board which set of time code data is to be cur-
rently "selected", and which set of time code data is to be located in a
separate area (reserved for this purpose) of the PCIe-TC board's memory.
Refer to the "PCIe-TC Board Reference Manual" if you need technical
information on register mapping, how to read time code from the board,
how to read two different time codes simultaneously, etc..
PCIe-TC User Guide Page 18 April 2012

LTC GENERATOR OPERATIONS

The LTC generator output signal appears at connector J2. The LTC gen-
erator can be freerunning, or synchronized to the LTC reference signal at
J1, or synchronized to the VIDEO reference signal at J3. With the excep-
tion of some generator-only boards, your PCIe-TC board will power up
with the generator(s) turned off, and you will have to run a third party
application program, our Windows test/demo program (on the CDROM),
or the bootable test/demo program (on the CDROM) to get it running.
The generator always remembers what mode it was in when power was
turned off, and powers back up in the same mode. Thus if you were gen-
erating EBU (25fps) LTC when the power was turned off, the board will
come back up in EBU mode even if the EBU reference signal (LTC or
VIDEO) is no longer present. If a VIDEO reference signal changes from
PAL to NTSC, for example, the board will automatically switch over to
SMPTE mode. It works the other way around too, and with 24fps LTC.
The best way to see how the LTC generator works is to fire up the Win-
dows test/demo program (from the CDROM) and enable the LTC genera-
tor. You will be able to set the time bits, the user bits, start and stop the
generator, and select a sync source.
The LTC generator is "smart" in that it continuously adjusts its output
frequency to stay in phase with the selected LTC or VIDEO reference
signal. After a 5 minute initial "learning" period, if the LTC or VIDEO
reference disappears, the LTC generator will continue generating LTC
with a maximum frequency error of +0.004% (4 frames/hour). This figure
assumes that the board's operating temperature and voltage remain fairly
stable, and gives TV station operators (for example) plenty of time to get
the reference signal hooked back up before the LTC generator's frequency
drift becomes noticeable. The board remembers this calibration data even
when the power is turned off, and maintains separate constants for
SMPTE, EBU, and FILM, using both LTC and VIDEO references.
PCIe-TC User Guide Page 19 April 2012