GS4911B Datasheet, PDF (64/113 Pages) Gennum Corporation – HD/SD/Graphics Clock and Timing Generator with GENLOCK

GS4911B/GS4910B Data Sheet
Table 3-8: Audio Clock Divider
ACLKn_fs_Multiple[3:0]
Audio Clock Frequency
000
fs
001
64fs
010
128fs
011
192fs*
100
256fs
101
384fs*
110
512fs**
111
z-bit
*This setting is only available when the enable_384fs bit of the Audio_Control register is HIGH.
**512fs clock will have a 33% duty cycle when the enable_384fs bit is HIGH and fs = 96kHz.
The fs signal on ACLK1-3 has an accurate 50% duty cycle, and can be used for
left/right definition, with the following exception: if fs = 96kHz and the user
configures the host interface such that one of the three ACLK pins is set to output
a clock signal at 192fs or 384fs, the 512fs clock will have a 33% duty cycle.
All audio clocks are initially reset on the rising edge of the AFS pulse, ensuring that
video to audio clock synchronization is correct. During normal operation, the audio
clock edge is allowed to drift slightly with respect to the AFS pulse. By default, the
audio clock will be reset directly by the AFS pulse if it drifts more than
approximately +/-0.1us from the rising edge of the AFS pulse. However, after
device reset, or after the application of a new input reference, the ACLK outputs
may sometimes be offset from the AFS pulse by up to several microseconds. The
offset will remain until the device is reset or the reference removed and re-applied.
The user may avoid this offset by minimizing the width of the AFS_Reset_Window
using bits 9-7 of register 31h for the duration of the audio PLL locking process.
Once the audio PLL is locked, bit 1 of register 1Fh will be set HIGH, and the
AFS_Reset_Window may be set as desired. See Table 3-9.
NOTE: To maintain correct audio clock frequencies for some VESA standards, the
window tolerance shown in Table 3-9 may have to be increased from its default
setting. In this case, set the AFS_Reset_Window register to 1XX.
36655 - 2 April 2006
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