GS4911B_09 Datasheet, PDF (64/119 Pages) Gennum Corporation – HD/SD/Graphics Clock and Timing Generator with GENLOCK

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.
GS4911B/GS4910B HD/SD/Graphics Clock and Timing
Generator with GENLOCK
Data Sheet
36655 - 5
June 2009
64 of 119