GS4910B GENNUM [Gennum Corporation], GS4910B Datasheet - Page 57

• Manufacturer Part Number: GS4910B
• Description: HD/SD/Graphics Clock and Timing Generator with GENLOCK
• Manufacturer: GENNUM [Gennum Corporation]

To genlock the audio clock to the video clock, the user must lock the fundamental
sampling frequency (f
accomplished by programming the set of integers (A_Feedback_Divide,
A_Reference_Divide) in the equation:
where:
f
f
A_Feedback_Divide = numerator of the divide ratio (host register 3Bh-3Ch)
A_Reference_Divide = denominator of the divide ratio (host register 3Dh-3Eh)
n = an integer constant
The integer constant, n, will depend on the fundamental audio sampling frequency.
It will be one of the three values as defined in
Table 3-5: Integer Constant Value
Before programming A_Feedback_Divide and A_Reference_Divide, the
numerator and denominator must be reduced to their lowest factors.
For example, to manually genlock a custom audio clock with a fundamental
sampling frequency of 42kHz to a 27MHz video clock, the following calculations are
necessary:
Therefore, program A_Feedback_Divide = 1792 and A_Reference_Divide = 1125.
Note that n=1024 when programming a custom audio clock (see
page
36655 - 2
------------------------------------------------- -
A_Reference_Divide
n = 1024
∴
A _Feedback_Divide
s
out
NOTES:
1. Enable_384fs corresponds to bit 5 of address 31h of the host interface. It is LOW by default.
2. ‘X’ signifies ‘don’t care.’ This bit will be ignored when determining n.
= the fundamental audio sampling frequency
------------------------------------------------- -
A_Reference_Divide
A _Feedback_Divide
ASR_SEL[2:0]=100b
= output video clock frequency
73).
YES
YES
April 2006
NO
=
=
n
1024
s
×
) to the frequency of the output video clock (f
------- -
f
out
f
s
×
----------------------- -
27000000
42000
Enable_384fs = 0
=
YES
NO
43008
-------------- -
27000
X
GS4911B/GS4910B Data Sheet
=
1792
----------- -
1125
Table
3-5.
Value of constant (n)
3072
1024
1536
Section 3.9.2 on
out
). This is
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