Cirrus Logic CS2300-OTP - Manual (Page 14)

CS2300-OTP
14 DS844F2
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.
5.4.4 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-Mod is applied accordingly.
The user defined ratio, ratio modifier, and automatic ratio modifier make up the effective ratio R
EFF
, the
final calculation used to determine the output to input clock ratio. The conceptual diagram in Figure 10
summarizes the features involved in the calculation of the ratio values used to generate the fractional-N
value which controls the Frequency Synthesizer. The subscript ‘4’ indicates the modal parameters.
Figure 10. Ratio Feature Summary
Referenced Control Parameter Definition
M[1:0] pins............................. “M1 and M0 Mode Pin Functionality” on page 16
Referenced Control Parameter Definition
Ratio 0-3................................ “Ratio 0 - 3” on page 20
M[1:0] pins............................. “M1 and M0 Mode Pin Functionality” on page 16
LFRatioCfg ............................ “Low-Frequency Ratio Configuration (LFRatioCfg)” on page 20
RModSel[1:0] ........................ “R-Mod Selection (RModSel[1:0])” section on page 19
Effective Ratio R
EFF
Ratio Format
Frequency Reference Clock
(CLK_IN)
PLL Output
Frequency
Synthesizer
Digital PLL &
Fractional N Logic
Ratio 0
Ratio 1
Ratio 2
Ratio 3
12.20
20.12
M[1:0] pins
LFRatioCfg
RModSel[1:0]
4
Ratio
Modifier
LCO
Dynamic Ratio, ‘N’
User Defined Ratio R
UD
M2 pin