GS4901B Datasheet, PDF (56/95 Pages) Gennum Corporation – SD Clock and Timing Generator with GENLOCK

GS4901B/GS4900B Preliminary Data Sheet
525i 59.94 Format
For 525/59.94 NTSC reference signals, the device will observe the 5-frame
phase-relationship inherent with this video standard, aligning the audio clocks with
the 50% point of the H sync input of line 1 on every fifth frame (+/- the allowable
drift specified in Table 3-9).
The number of audio sample clocks during a video frame is shown in Table 3-10
for 32, 44.1, and 48kHz audio sampling frequencies.
Table 3-10: Audio Sampling Frequency to Video Frame Rate Synchronization
Audio Sample Rate (kHz)
32
44.1
48
* fps = frames per second.
24fps
4000/3
3675/2
2000
25fps
1280
1764
1920
Audio Samples per Video Frame
29.97fps
16016/15
147147/100
8008/5
30fps
3200/3
1470
1600
50fps
640
882
960
59.94fps
8008/15
147147/200
4004/5
60fps
1600/3
735
800
The external 10FID input pin may be used to resynchronize other audio clock
frequencies, according to Table 3-10, by applying an active signal during the
reference HSYNC of line 1 of the appropriate video frame. Please see
Section 3.4.2 on page 41 for more details on the 10FID input pin.
In the case where 10FID is not present as a reference signal, the GS4901B will
automatically generate an AFS pulse appropriate to the format selected, and use
it to create an audio frame sequence.
Host Interface Control of AFS and 10FID
Alternatively, the user may program the device via the host interface to re-time the
audio frame sequence and 10 field-ID. Using register 1Ah, a pulse may be
generated to reset the AFS and/or 10FID dividers at the start of an output video
frame (see Section 3.10.3 on page 66).
If using the host interface to reset the AFS pulse, the device may be configured to
ignore the input 10FID reference pin. To disable the signal on the external 10FID
pin from resetting the AFS output pulse, set bit 0 of the Audio_Control register
HIGH.
If using the host interface to reset the 10FID pulse, the external 10FID pin must be
grounded.
37703 - 0 April 2006
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