GS4911B Datasheet, PDF (37/119 Pages) Gennum Corporation – HD/SD/Graphics Clock and Timing Generator with GENLOCK

3. Detailed Description
3.1 Functional Overview
The GS4911B/GS4910B is a highly flexible, digitally controlled clock synthesis circuit
and timing generator with genlock capability.
The device has two main modes of operation: Genlock mode and Free Run mode. In
Genlock mode, the video clock and timing outputs, will be frequency and phase locked
to the detected reference input signal. In Free Run mode, the occurrence of all
frequencies is based on a 27MHz external crystal reference.
The GS4911B/GS4910B will recognize input reference signals conforming to 36
different video standards and 16 different graphic formats. It supports cross-locking,
allowing the output to be genlocked to an incoming reference that is different from the
output video standard selected.
When the device is in Genlock mode and the input reference is removed, the
GS4911B/GS4910B will enter Freeze mode. In this mode, the output clock and timing
signals will maintain their previously genlocked phase and frequency to within +/-
2ppm.
The user may select to output one of 8 different video sample clock rates or 13 different
graphic display clock rates, or may program any clock frequency between 13.5MHz and
165MHz. The chosen clock frequency may be further internally divided, and is available
on two video clock outputs and one LVDS video clock output pair. The video clocks may
also be individually phase delayed with respect to the timing outputs for clock skew
control.
Eight user-selectable timing outputs are provided that can automatically produce the
following timing signals for 35 different video formats and 13 different graphics
formats: HSync, Hblanking, VSync, Vblanking, F sync, F digital, AFS (GS4911B only), DE,
and 10FID. Alternatively, custom output timing signals may be programmed in the host
interface.
In addition, the GS4911B provides three audio sample clock outputs that can produce
audio clocks up to 512fs with fs ranging from 9.7kHz to 96kHz. Audio to video phasing
is accomplished by either an external 10FID input reference, a 10FID signal specified via
internal registers, or a user-programmed audio frame sequence.
3.2 Modes of Operation
The GS4911B/GS4910B will operate in either Genlock mode or Free Run mode
depending on the setting of the GENLOCK pin. These two modes are described in
Section 3.2.1 on page 38 and Section 3.2.2 on page 41 respectively.
If desired, the external GENLOCK pin may be ignored by setting bit 5 of the
Genlock_Control register (address 16h) so that genlock can instead be controlled via the
host interface (see Section 3.12.3 on page 79). Although the external GENLOCK pin will
be ignored in this case, it should not be left floating.
GS4911B/GS4910B HD/SD/Graphics Clock and Timing
Generator with GENLOCK
Data Sheet
36655 - 5
June 2009
37 of 119