GS4910B GENNUM [Gennum Corporation], GS4910B Datasheet - Page 55

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

where:
f
f
H_Feedback_Divide = numerator of the divide ratio (host register 28h-29h)
H_Reference_Divide = denominator of the divide ratio (host register 2Ah-2Bh)
Before programming H_Feedback_Divide and H_Reference_Divide, the
numerator and denominator must be reduced to their lowest factors.
For example, to manually genlock an output format with a 74.25MHz video clock to
a reference with a 27MHz video clock and 1716 clocks per line, the following
calculations are necessary:
Therefore, program H_Feedback_Divide = 4719 and H_Reference_Divide = 1.
Output Line/Frame Reset Host Registers
In addition to programming H_Feedback_Divide and H_Reference_Divide, the
user must also define the ratio of the output frame rate to the reference frame rate.
The denominator of this ratio is programmed in the Output_FV_Reset register at
address 18h of the host interface. Before Output_FV_Reset is programmed, the
numerator and denominator must be reduced to their lowest factors. Two
examples are demonstrated below:
Example 1: the reference has a frame rate of 30Hz and the output frame rate is
50Hz:
Therefore, program Output_FV_Reset = 3. The numerator does not have to be
programmed.
Example 2: the reference has a frame rate of 29.97Hz and the output frame rate is
50Hz:
Therefore, program Output_FV_Reset = 600. The numerator does not have to be
programmed.
Additionally, the Frame_Divider_Reset register (address19h) must be configured
to initialize the counter reset programmed in register 18h.
36655 - 2
∴
Output Frame Rate
--------------------------------------------- -
f
Output Frame Rate
--------------------------------------------- -
out
Href
Input Frame Rate
Href
Input Frame Rate
------------------------------------------------- -
H_Reference_Divide
H_Feedback_Divide
= output video clock frequency
= reference H pulse frequency on HSYNC
=
----------- - MHz
1716
27
April 2006
=
=
=
50
----- -
30
------------ -
29.97
50
74.25MHz
------------------------- -
=
----------- - MHz
1716
27
5
-- -
3
=
1001
----------- -
600
=
74.25
×
1716
----------- -
GS4911B/GS4910B Data Sheet
27
=
127413
----------------- -
27
=
4719
----------- -
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