CS2000-CP
9. CALCULATING THE USER DEFINED RATIO
Note: The software for use with the evaluation kit has built in tools to aid in calculating and converting the User
Defined Ratio. This section is for those who are not interested in the software or who are developing their
systems without the aid of the evaluation kit.
Most calculators do not interpret the fixed point binary representation which the CS2000 uses to define the output
to input clock ratio (see Section 5.3.1 on page 19); However, with a simple conversion we can use these tools to
generate a binary or hex value which can be written to the Ratio registers.
0-3
9.1
High Resolution 12.20 Format
To calculate the User Defined Ratio (R ) to store in the register(s), divide the desired output clock frequen-
UD
20
cy by the given input clock (CLK_IN or RefClk). Then multiply the desired ratio by the scaling factor of 2
to get the scaled decimal representation; then use the decimal to binary/hex conversion function on a cal-
culator and write to the register. A few examples have been provided in Table 2.
Scaled Decimal
Representation =
(output clock/input clock) • 2
1288490
Hex Representation of
Desired Output to Input Clock Ratio
(output clock/input clock)
20
Binary R
UD
12.288 MHz/10 MHz=1.2288
11.2896 MHz/44.1 kHz=256
00 13 A9 2A
10 00 00 00
268435456
Table 2. Example 12.20 R-Values
9.2
High Multiplication 20.12 Format
To calculate the User Defined Ratio (R ) to store in the register(s), divide the desired output clock frequen-
UD
12
cy by the given input clock (CLK_IN). Then multiply the desired ratio by the scaling factor of 2 to get the
scaled decimal representation; then use the decimal to binary/hex conversion function on a calculator and
write to the register. A few examples have been provided in Table 3.
Scaled Decimal
Representation =
(output clock/input clock) • 2
838860800
Hex Representation of
Desired Output to Input Clock Ratio
(output clock/input clock)
12
Binary R
UD
12.288 MHz/60 Hz=204,800
32 00 00 00
2D F5 E2 08
11.2896 MHz/59.97 Hz =188254.127...
771088904
Table 3. Example 20.12 R-Values
34
DS761F1
CIRRUS [ CIRRUS LOGIC ]
