Cirrus Logic CS2100-OTP - Manual (Page 15)

CS2100-OTP
DS841F2 15
5.4.2 Ratio Modifier (R-Mod)
The Ratio Modifier is used to internally multiply/divide the currently addressed R
UD
(Ratio
0-3
stored in the
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 18 ).
Table 2. Ratio Modifier
5.4.3 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
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.
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
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 21
RModSel[1:0] ........................ “R-Mod Selection (RModSel[1:0])” section on page 20
M2Config[2:0]........................ “M2 Pin Configuration (M2Config[2:0])” on page 22
Referenced Control Parameter Definition
M[1:0] pins............................. “M1 and M0 Mode Pin Functionality” on page 17