CS2000-OTP

16

DS758PP1

It is important to note that Auto R-Mod (if enabled) is applied in addition to any R-Mod already selected

by the RModSel[1:0] modal parameter and is used to calculate the Effective Ratio (see Section 5.4.5 on

page 16).

Auto R-Mod can be used to generate the appropriate oversampling clock (MCLK) for audio A/D and D/A

converters. For example, if the clock applied to CLK_IN is the audio sample rate, Fs (also known as the

word, frame or Left/Right clock), and SysClk is 12.288 MHz (REF_CLK = 12.288 MHz with RefClkDiv[1:0]

generates the audio oversampling clocks as shown in Table 4.

Table 4. Example Audio Oversampling Clock Generation from CLK_IN

5.4.5

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.

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 unless auto

clock switching is enabled in which case the LockClk[1:0] modal parameter also selects the ratio (see

“Fractional-N Source Selection” on page 16).

5.4.6

Fractional-N Source Selection

To select between the static ratio based Frequency Synthesizer Mode and the dynamic ratio based Hybrid

PLL Mode, the source for the fractional-N value for the Frequency Synthesizer must be changed. The

Fractional-N value can either be sourced directly from the Effective Ratio (static ratio) or from the output

of the Digital PLL (dynamic ratio) (see Figure 12 on page 18). The setting of this function can be made

manual or automatically depending on the presence of CLK_IN.

FsDetect[1:0]

Inferred Audio Sample Rate

when SysClk = 12.288 MHz

Speed Mode (used for

audio converters)

Audio Oversampling

Clock

00

< 54.8 kHz

Single Speed

512 x

01

54.8 kHz to 128 kHz

Double Speed

256 x

10

> 128 kHz

Quad Speed

128 x

Referenced Control

Parameter Definition

Ratio 0-3................................“Ratio 0 - 3” on page 24

RModSel[1:0] ........................“R-Mod Selection (RModSel[1:0])” section on page 23

AutoRMod .............................“Auto R-Modifier Enable (AutoRMod)” on page 24

M2Config[2:0]........................“M2 Pin Configuration (M2Config[2:0])” on page 26

Referenced Control

Parameter Definition

M[1:0] pins.............................“M1 and M0 Mode Pin Functionality” on page 20

LockClk[1:0] ..........................“Lock Clock Ratio (LockClk[1:0])” section on page 24