GS4911B Datasheet, PDF (50/113 Pages) Gennum Corporation – HD/SD/Graphics Clock and Timing Generator with GENLOCK

GS4911B/GS4910B Data Sheet
3.6 Genlock
When both the REF_LOST output and the GENLOCK input are LOW, the device
will attempt to genlock the output clock and timing signals to the input reference.
NOTE: The user must apply a reference to the input of the device prior to setting
GENLOCK = LOW. If the GENLOCK pin is set LOW and no reference signal is
present, the generated clock and timing outputs of the device may correspond to
the internal default settings of the chip until a reference is applied.
The device will first attempt to automatically genlock the output to the input
reference. This automatic locking process is described in Section 3.6.1 on
page 50. If the output format selected is such that it is not commonly genlocked to
the input reference, the GS4911B/GS4910B will not automatically lock. In this
case, the user may program designated registers to manually allow locking to
occur. The manual locking process is described in Section 3.6.2 on page 54.
The user may disable one or more of the recognized input standards from being
used to genlock the output by setting the Reference_Standard_Disable register
located at address 11h - 14h of the host interface. If a reference is applied that is
disabled in the Reference_Standard_Disable register, both the automatic and
manual locking process will fail when the application layer sets GENLOCK = LOW.
NOTE: If the device is already genlocked to an input reference and the applied
standard is subsequently disabled in the Reference_Standard_Disable register,
the device will remain locked.
3.6.1 Automatic Locking Process
The behaviour of the device when attempting to automatically genlock will depend
on the status and format of the input reference with respect to the selected output
format.
VID_STD[5:0] = 1 to 51:
Once reference validity is established and the reference format is recognized, the
device uses an internal cross-reference genlock look-up table to determine
whether the input can be used to genlock the output. A simplified version of this
look-up table is shown in Table 3-4. The table represents a matrix with the
VID_STD[5:0] number representation of each possible reference format along the
top axis, and the VID_STD[5:0] representation of each possible output timing
format along the vertical axis. A shaded box indicates that the output format can be
automatically genlocked to the input reference.
If the device determines that the output can be automatically genlocked to the input
reference, it will lock the output format to the reference, adjust the output timing
signals based on the genlock timing offset registers (Section 3.2.1.1 on page 37),
and then set the LOCK_LOST pin LOW.
36655 - 2 April 2006
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