GS4901B_09 Datasheet, PDF (47/102 Pages) Gennum Corporation – SD Clock and Timing Generator with GENLOCK

generated clock and timing outputs of the device may correspond to the internal default
settings of the chip until a reference is applied.
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.
If the device cannot automatically genlock the output to the applied reference, the
LOCK_LOST pin will be set HIGH and the device will operate in Free Run mode.
Individual H, V, and F-locked signals can be read from the Genlock_Status register of the
host interface. Additionally, designated bits in the Genlock_Control register may be
configured to permit the genlock block to ignore invalid timing on the HSYNC, VSYNC,
or FSYNC pin when determining the locked status of the device. These registers are
described in Section 3.9.3 on page 66.
The user may disable one or more of the 36 video standards listed in Table 1-2 from
being used to genlock the output by setting the Reference_Standard_Disable register
located at address 11h-13h of the host interface. If a reference is applied that is disabled
in the Reference_Standard_Disable register, the lock process will fail when the
application layer sets GENLOCKb = 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.
By default, the HD video reference formats are disabled in the
Reference_Standard_Disable register and so must be enabled by the user before
attempting to lock to an HD reference. See Section 1.4 on page 19.
Table 3-4: Cross-reference Genlock Table
Input Reference Format
1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 25 26 27 29 30 31 32 33 34 35 36 37 38
1
3
4
5
6
7
8
9
10
GS4901B/GS4900B SD Clock and Timing Generator
with GENLOCK
Data Sheet
37703 - 4
December 2009
47 of 102