571AMC000154DG Silicon Laboratories Inc, 571AMC000154DG Datasheet - Page 15

• Manufacturer Part Number: 571AMC000154DG
• Manufacturer: Silicon Laboratories Inc

Specifications of 571AMC000154DG

• Lead Free Status / Rohs Status: Compliant

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,
3. Unfreeze the DCO and assert the NewFreq bit (bit 6
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.
f
Read the current values for RFREQ, HS_DIV, N1:
RFREQ
11744124600d x 2
HS_DIV = 4
N1 = 8
out
HS_DIV, N1)
of Register 135) within the maximum Unfreeze to
NewFreq Timeout specified in Table 12,
“Programming Constraints and Timing,” on page 12.
= 156.25 MHz
current
Convert integer portion to a 10-bit binary number
= 0x2BC011EB8h = 11744124600d,
Figure 4. Example of RFREQ Decimal to Hexadecimal Conversion
28
= 43.7502734363d
46 = 00 0010 1110b
00 0010 1110 0000 1011 0000 0100 1100 1110 0000b
Concatenate the two results
02E0B04CE0h
46.043042064
Convert to Hex
Rev. 1.2
Convert to a 28-bit binary number (pad 0s on the left)
Calculate f
Given
dividers that will keep f
5.67 GHz. In this case, keeping the same output
dividers will still keep f
Calculate the new value of RFREQ given the new DCO
frequency:
f
0000 1011 0000 0100 1100 1110 0000
f
DCO_current
DCO_new
=
Multiply the fractional portion by 2
.043042064 x 2
161.1328125 MHz 4
Truncate the remaining fractional portion
f
out_new
RFREQ
=
f
XTAL
XTAL
0x2D1E12788
=
=
, f
f
=
out_new
= 161.1328125 MHz,
f
new
DCO_current
out
-------------------------------------- -
RFREQ
f
28
DCO_current

= 11554016
=
= 11554016.077
HSDV
DCO

f
---------------------- -
DCO_new
DCO
HSDV

f
current
XTAL
within its range limits:


within the range of 4.85 to
Si570/Si571
8
N1
new
=
=
=
5.156250000 GHz
=

114.285 MHz
45.11746934
28
N1
5.000000000 GHz
new
choose
output
15