CDK2000 datasheet(13/26 Pages) CIRRUS

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CS2200-CP

DS759F1

5.2.2

Ratio Modifier (R-Mod)

The Ratio Modifier is used to internally multiply/divide the RUD (the Ratio stored in the register space re-

mains unchanged). The available options for RMOD are summarized in Table 1 on page 13.

The R-Mod value selected by RModSel[2:0] is always used in the calculation for the Effective Ratio

(REFF), see “Effective Ratio (REFF)” on page 13. If R-Mod is not desired, RModSel[2:0] should be left at

its default value of ‘000’, which corresponds to an R-Mod value of 1, thereby effectively disabling the ratio

modifier.

Table 1. Ratio Modifier

5.2.3

Effective Ratio (REFF)

The Effective Ratio (REFF) is an internal calculation comprised of RUD and the appropriate modifiers, as

previously described. REFF is calculated as follows:

REFF = RUD

• 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 REFF should not be used; For example

if RUD is 1024 an RMOD of 8 would produce an REFF value of 8192 which exceeds the 4096 limit of the

12.20 format. In all cases, the maximum and minimum allowable values for REFF are dictated by the fre-

quency limits for both the input and output clocks as shown in the “AC Electrical Characteristics” on

page 7.

RModSel[2:0]

Ratio Modifier

000

001

010

011

100

0.5

101

0.25

110

0.125

111

0.0625

Referenced Control

Ratio...................................... “Ratio (Address 06h - 09h)” on page 21

RModSel[2:0] ........................ “R-Mod Selection (RModSel[2:0])” section on page 20

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