Si5338-RM
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Equation 1. Frequency Programming
Register values for MSx_P1, MSx_P2, and MSx_P3 must be written to the appropriate registers as shown in
Figure 4 and Figure 5. To ensure that the MultiSynth is properly configured, it is recommended to write all bytes
(even ones that are zero) associated with MSx_P1, MSx_P2, and MSx_P3. This will ensure that previous
configurations are completely overwritten.
Note: MSx_P1, MSx_P2, and MSx_P3 were named INT, NUM, and DEN in an earlier version of this document. Because the
values are not equal to the integer, numerator, and denominator, the names have been changed. The equations are
identical.
a +
b
c
Let MSn or MSx =
Example:
MSx_P1 = Floor
c
(a * c + b) * 128
- 512
Mod
b * 128 , c
MSx_P3 = c
The Floor function rounds down to the closest integer value.
Mod(b*128,c) returns the remainder of b*128/c
Note:
Where a = 4, 6, 8, 9 … 567
b = 0 … (2
30
-1)
c = 1 … (2
30
-1)
Note: When MSn or MSx is an integer, you must set b = 0 and c = 1
MSx_P2 =
a + b/c = 99.5328
MSx_P1 = 12228 (0x02FC4)
MSx_P2 = 124 (0x0000007C)
MSx_P3 = 625 (0x00000271)
a = 99, b=333, c=625
Alternately let a = 99, b = 5328, c=10000
MSx_P1 = 12228 (0x02FC4)
MSx_P2 = 1984 (0x0000007C0)
MSx_P3 = 10000 (0x000002710)
Both results can be used to program the Si5338
because in both cases b/c = .5328
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