Si5345-44-42-D-RM
Si5345
Rev. 1.0
103
14.3.3. Page 2 Registers Si5345
The clock that is present on XAXB pins is used to create an internal frequency reference for the PLL. The
XAXB_FREQ_OFFSET word is used to adjust this frequency reference with high resolution.
XAXB_FREQ_OFFSET can be used to compensate for the XTAL frequency error. This will cause the free run
frequency to be more accurate. It is programmed as a two’s complement number. This register can be used to
adjust the frequency of the VCO when it is locked to the XAXB frequency. ClockBuilder Pro calculates the correct
values for these registers.
0 = pre-scale value 1
1 = pre-scale value 2
2 = pre-scale value 4
3 = pre-scale value 8
This can only be used with external clock sources, not crystals.
This set of registers configures the P-dividers which are located at the four input clocks seen in Figure 2, “Si5342
DSPLL and Multisynth System Flow Diagram,” on page 11. ClockBuilder Pro calculates the correct values for the
P-dividers.
Register 0x0202-0x0205 XAXB Frequency Adjust
Reg Address
Bit Field
Type
Name
Description
0x0202
7:0
R/W
XAXB_FREQ_OFFSET
32 bit offset adjustment
0x0203
15:8
R/W
XAXB_FREQ_OFFSET
0x0204
23:16
R/W
XAXB_FREQ_OFFSET
0x0205
31:24
R/W
XAXB_FREQ_OFFSET
Register 0x0206 Pre-scale Reference Divide Ratio
Reg Address
Bit Field
Type
Name
Description
0x0206
1:0
R/W
PXAXB
Sets the prescale divider for the
input clock on XAXB.
Register 0x0208-0x020D P0 Divider Numerator
Reg Address
Bit Field
Type
Name
Description
0x0208
7:0
R/W
P0_NUM
48-bit Integer Number
0x0209
15:8
R/W
P0_NUM
0x020A
23:16
R/W
P0_NUM
0x020B
31:24
R/W
P0_NUM
0x020C
39:32
R/W
P0_NUM
0x020D
47:40
R/W
P0_NUM