GS4911B_09 Datasheet, PDF (50/119 Pages) Gennum Corporation – HD/SD/Graphics Clock and Timing Generator with GENLOCK

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 38), and then set the
LOCK_LOST pin LOW.
GS4911B/GS4910B HD/SD/Graphics Clock and Timing
Generator with GENLOCK
Data Sheet
36655 - 5
June 2009
50 of 119