GS4911B Datasheet, PDF (54/113 Pages) Gennum Corporation – HD/SD/Graphics Clock and Timing Generator with GENLOCK

GS4911B/GS4910B Data Sheet
3.6.2 Manual Locking Process
Using the host interface, the GS4911B/GS4910B may be manually programmed to
genlock certain video formats and audio clocks that are not automatically
genlocked by the device. The following sections discuss when the user should
manually program the internal video and/or audio genlock block, and how these
blocks are programmed.
3.6.2.1 Programming the Internal Video Genlock Block and Output Line/Frame Reset Registers
The user will be required to manually program the internal video genlock block and
output line/frame reset registers during any of the following situations:
1. The pre-programmed output format and input reference cannot be
automatically genlocked according to the cross-reference genlock table
(Table 3-4 in Section 3.6.1 on page 50).
2. A custom video clock is programmed in the host interface (Section 3.9.1 on
page 72).
3. VID_STD[5:0] = 62 and a custom H-based timing output signal is programmed
(see Section 3.10 on page 74).
4. VID_STD[5:0] = 62 and a custom reference pulse is applied to HSYNC (see
Section 3.10.1 on page 74).
Video Genlock Block Host Registers
A simplified version of the GS4911B/GS4910B’s internal video genlock block is
shown in Figure 3-6.
27MHz
HSYNC
(f_Href
Internal Video Genlock Block
H_Reference_Divide
(host address 2Ah - 2Bh)
Phase
Comparator
Clock
Synthesizer
Output Video
Clock
(fout
H_Feedback_Divide
(host address 28h - 29h)
Figure 3-6: Internal Video Genlock Block
To genlock the output clock and video timing signals to the input format, the user
must first lock the frequency of the output video clock (f_out) to the frequency of the
reference pulse on HSYNC (f_Href). This is accomplished by programming the set of
integers (H_Feedback_Divide, H_Reference_Divide) in the equation:
-^H----^_---^F----^e---^e--^d---^b---^a---^c---^k---^_---^D----ⁱ--^v--ⁱ--^d---^e- = --^f--^o---^u--^t-
H_Reference_Divide f_Href
36655 - 2 April 2006
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