參數(shù)資料
型號: 570AAB000107DG
廠商: SILICON LABORATORIES
元件分類: XO, clock
英文描述: CRYSTAL OSCILLATOR, CLOCK, 10 MHz - 810 MHz, LVPECL OUTPUT
封裝: ROHS COMPLIANT PACKAGE-8
文件頁數(shù): 7/30頁
文件大?。?/td> 361K
代理商: 570AAB000107DG
Si570/Si571
Rev. 1.1
15
Figure 4. Example of RFREQ Decimal to Hexadecimal Conversion
Once the new values for RFREQ, HSDIV, and N1 are
determined, they can be written directly into the device
from the serial port using the following procedure:
1. Freeze the DCO (bit 4 of Register 137)
2. Write the new frequency configuration (RFREQ,
HS_DIV, N1)
3. Unfreeze the DCO and assert the NewFreq bit (bit 6
of Register 135) within the maximum delay specified
The process of freezing and unfreezing the DCO will
cause the output clock to momentarily stop and start at
any arbitrary point during a clock cycle. This process
can take up to 10 ms. Circuitry that is sensitive to
glitches or runt pulses may have to be reset after the
new frequency configuration is written.
Example:
An Si570 generating 156.25 MHz must be re-configured
to generate a 161.1328125 MHz clock (156.25 MHz x
66/64). This frequency change is greater than
±3500 ppm.
fout =156.25MHz
Read the current values for RFREQ, HS_DIV, N1:
RFREQcurrent = 0x2BC011EB8h = 11744124600d,
11744124600d x 228 = 43.7502734363d
HS_DIV = 4
N1 = 8
Calculate fXTAL, fDCO_current
Given fout_new = 161.1328125 MHz, choose output
dividers that will keep fDCO within the range of 4.85 to
5.67 GHz. In this case, keeping the same output
dividers will still keep fDCO within its range limits:
Calculate the new value of RFREQ given the new DCO
frequency:
46.043042064
Convert integer portion to a 10-bit binary number
46 = 00 0010 1110b
Concatenate the two results
00 0010 1110 0000 1011 0000 0100 1100 1110 0000b
Convert to Hex
02E0B04CE0h
Multiply the fractional portion by 228
.043042064 x 228 = 11554016.077
Truncate the remaining fractional portion
= 11554016
Convert to a 28-bit binary number (pad 0s on the left)
0000 1011 0000 0100 1100 1110 0000
fDCO_current
fout HSDV
×
N1
×
5.000000000 GHz
==
fXTAL
fDCO_current
RFREQcurrent
---------------------------------------
114.285 MHz
==
fDCO_new
fout_new HSDVnew
×
N1new
×
161.1328125 MHz 4
×
8
×
5.156250000 GHz
=
==
RFREQnew
fDCO_new
fXTAL
-----------------------
45.11746934
0x2D1E12788
=
==
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