Chapter 4: Using the USD 45
Requirements for Read/Regeneration of LTC,
VITC and MTC
LTC
The external positional reference must
be moving at normal, 1x forward speed
(±8%).
VITC The positional reference must be LTC
or Bi-Phase/Tach, at any readable speed,
forward or reverse, or when the positional
reference is set to Generate. The USD will
not regenerate VITC if the positional refer-
ence is VITC.
MTC In order for the USD to regenerate
continuous MTC, the external positional
reference must be moving at normal, 1x
forward speed (±8%). Outside of this speed
range and direction, MTC is generated in
bursts every 200 milliseconds. This allows
MTC-slaved devices to read VITC or Bi-
Phase properly in either direction, and at
speeds down to zero. The USD begins re-
generating MTC as soon as it again detects
a valid positional reference signal.
✽ To optionally mute idle time MTC output,
see “MTC Output and Idle Muting” on
page 51.
If the positional reference is LTC or VITC,
USD will regenerate time code addresses
that match the incoming time code ad-
dresses. If the positional reference is a Bi-
Phase/Tach signal, the USD will generate
time code addresses starting at the Bi-Phase
preset start time. (See “Bi-Phase/Tach Start-
ing Frame” on page 42 for more informa-
tion.)
Generator Preset Mode
In this mode, the USD generates time code
internally from a start time based upon the
Generator Preset Time. Using either
USD Setup or the front panel controls, you
can start, stop, resume, and reset time code
generation.
When generating time code in Generator
Preset Mode, the USD time code generator
is resolved (locked) to one of three possible
sources, based upon the following Genera-
tor Reference rule.
Generator Reference Rule
◆ If the Clock Reference is set to Internal,
LTC, Pilot Tone, Bi-Phase/Tach, Digital
(AES/EBU), Digital (Super Clock), or Digital
(Word Clock), then the time code genera-
tor will lock to the selected clock reference.
– or –
◆ If the Clock Reference is set to one of the
two video inputs (Video Ref In or Video In),
then the time code generator will reference
the Video Ref In connector.
24 fps and Frame Rate Restrictions
24 FPS cannot be used as the USD time
code format when the Positional Reference
is set to Generate and the Clock Reference
is either one of the two video inputs.
Furthermore, under these same conditions,
if the video format is set to NTSC, only
29.97 FPS and 29.97 DF FPS may be chosen
as the time code format, and, if the video
format is set to PAL, only 25 FPS may be
chosen as the time code format.
These restrictions are removed when not in
Generate mode.
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