CS2100-OTP Datasheet, PDF (16/28 Pages) Cirrus Logic – Fractional-N Clock Multiplier

CS2100-OTP
set to ‘10’), FsDetect[1:0] would then reflect the frequency range of the audio sample rate. An R_UD of 512
generates the audio oversampling clocks as shown in Table 4.
FsDetect[1:0]
00
01
10
Inferred Audio Sample Rate
when SysClk = 12.288 MHz
< 54.8 kHz
54.8 kHz to 128 kHz
> 128 kHz
Speed Mode (used for
audio converters)
Single Speed
Double Speed
Quad Speed
Audio Oversampling
Clock
512 x
256 x
128 x
Table 4. Example Audio Oversampling Clock Generation from CLK_IN
Referenced Control
Parameter Definition
Ratio 0-3................................“Ratio 0 - 3” on page 22
RModSel[1:0] ........................“R-Mod Selection (RModSel[1:0])” section on page 21
AutoRMod .............................“Auto R-Modifier Enable (AutoRMod)” on page 22
M2Config[2:0]........................“M2 Pin Configuration (M2Config[2:0])” on page 24
5.4.4
Effective Ratio (R_EFF)
The Effective Ratio (R_EFF) is an internal calculation comprised of R_UD and the appropriate modifiers, as
previously described. R_EFF is calculated as follows:
R_EFF = R_UD • R-Mod • Auto R-Mod
To simplify operation the device handles some of the ratio calculation functions automatically (such as
when the internal timing reference clock divider is set). For this reason, the Effective Ratio does not need
to be altered to account for internal dividers.
Ratio modifiers which would produce an overflow or truncation of R_EFF should not be used. In all cases,
the maximum and minimum allowable values for R_EFF are dictated by the frequency limits for both the
input and output clocks as shown in the “AC Electrical Characteristics” on page 7.
Selection of the user defined ratio from the four stored ratios is made by using the M[1:0] pins.
Referenced Control
Parameter Definition
M[1:0] pins.............................“M1 and M0 Mode Pin Functionality” on page 18
5.4.5
Ratio Configuration Summary
The R_UD is the user defined ratio for which up to four different values (Ratio_0-3) can be stored in the one
time programmable memory. The M[1:0] pins then select the user defined ratio to be used as well as the
modal configuration set. The resolution/format for the R_UD is selectable. R-Mods are applied according to
their settings. The user defined ratio, ratio modifier, and automatic ratio modifier make up the effective
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