CS2000-OTP

DS758F1

15

5.4.3

Ratio Modifier (R-Mod)

register space remain unchanged). The available options for R-Mod are summarized in Table 2 on

page 15. R-Mod is enabled via the M2 pin in conjunction with the appropriate setting of the M2Config[2:0]

global parameter (see Section 5.7.2 on page 19).

Table 2. Ratio Modifier

5.4.4

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 15).

5.4.5

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 13 on page 17). The setting of this function can be made

manual or automatically depending on the presence of CLK_IN.

RModSel[1:0]

R Modifier

00

0.5

01

0.25

10

0.125

11

0.0625

Referenced Control

Parameter Definition

Ratio 0-3................................“Ratio 0 - 3” on page 23

RModSel[1:0] ........................ “R-Mod Selection (RModSel[1:0])” section on page 22

M2Config[2:0]........................“M2 Pin Configuration (M2Config[2:0])” on page 25

Referenced Control

Parameter Definition

M[1:0] pins............................. “M1 and M0 Mode Pin Functionality” on page 19

LockClk[1:0] .......................... “Lock Clock Ratio (LockClk[1:0])” section on page 23