PCIe-TC User Guide Page 14 April 2012
RELIABILITY ESTIMATE
MTBF (mean time before failure) for PCIe-TC boards is unknown at
present, because this is a relatively new product for us. Our previous
(PCI-TC) generation of time code boards had an actual MTBF of approxi-
mately 450 years, based on actual product return rates. Our PCIe-TC
boards are very similar in design and construction, so should be about the
same. Note that these numbers are well in excess of the expected useful
product lifetime.
STATUS LED OPERATIONS
The green colored status LED, near the bottom end of the PCIe-TC board
bracket, is useful for quickly diagnosing signal quality problems. If the
board is reading time code successfully (either LTC or VITC), the green
status LED will be solid “on”. If both LTC and VITC are missing, but the
video input signal is OK, the green status LED will be “on” most of the
time, but will blink off once per second. If the green status LED is off all
the time, then the board is not seeing any valid inputs.
Intermittent input signals can cause the green status LED to blink off
occasionally. For example, if a board is reading LTC OK, then the LTC
input signal drops out momentarily, the green status LED will blink off
for as long as the LTC input signal remains unreadable.
For more advanced users, it is possible in some cases for the green status
LED to remain off even if a valid input signal is present. For example, if
a PCIe-VLTC/RDA board is placed into “VITC Reader” mode via applica-
tion software, and only an LTC input signal is connected to the board, the
green status LED will remain off because in that particular case, the board
is not reading any valid time code (the LTC reader function has been tem-
porarily disabled via application software). If in doubt, reboot the PC to
ensure that all readers are active (the power-on default setting).
PCIe-TC User Guide Page 15 April 2012
LTC READER OPERATIONS
PCIe-TC boards use proprietary hardware and software to read LTC from
the signal present at connector J1. As described in the INSTALLATION
section of this manual, the LTC input connector can be either an RCA jack
(standard equipment), a Mini-XLR(m) connector, or an isolated BNC(f)
connector. Depending on the LTC signal quality, which varies from one
tape machine to the next, our PCIe-TC boards can read LTC at tape speeds
from 1/30x to 80x play speed. With most VTR outputs, reading LTC at
tape speeds which are below 1/5x play speed is doubtful.
The LTC input signal is first passed through a differential amplifier and a
band pass filter to remove DC offsets, high frequency noise, and common
mode noise. The cleaned up LTC input signal can be viewed at the “LTC1”
test point on the board (includes a +1.4V DC offset, may be clipped). This
signal is then passed through a window comparator to convert the analog
waveform into a digital signal for further analysis. The window compara-
tor has a threshold which increases as the LTC signal amplitude increases,
thus providing very good noise rejection for normal amplitude (1Vpp to
2Vpp) LTC input signals. The digitized LTC input signal is then analyzed
using a combination of hardware and software to extract the desired time
bits, user bits, and embedded bits information.
Because the SMPTE and EBU and FILM longitudinal time codes are so
similar, the PCIe-TC board will read any of these LTC formats interchange-
ably. No setup work needs to be done.
If you are having trouble reading LTC, first try the bootable test/demo
program on the PCIe-TC CDROM. Be sure the cable and connectors you
are using are of good quality and are wired correctly. Use a continuity
tester if necessary to check them out. Connect one end of the cable to J1,
the LTC input on your PCIe-TC board, as described in the INSTALLA-
TION section of this manual. Connect the other end of the cable to the
“LTC OUTPUT” of the signal source. Because LTC is a specialized type of
audio signal, and can thus be recorded onto any audio channel, you may
have to experiment around to find out which channel has LTC on it.
Refer to the “PCIe-TC Board Reference Manual” if you need technical
information on register mapping, how to read time code from the board,
etc..
