DE5-NET
User
Manual
71
June 20, 2018
end
Users can get a desired frequency output from si570 by modifying these three parameters :
new_hs_div
,
new_n1
and
fdco
.
Detailed calculation method is in following equation:
fdco = output frequency * new_hs_div * new_n1 * 64
There are three constraints for the equation:
1.
4850 < output fequency * new_hs_div * new_n1 < 5600
2.
4 <= new_hs_div <= 11
3.
1 <= new_n1 < =128
For example, you want to get a 133.5 mhz clock, then
fdco = 133.5 x 4 x 10 x 64 = 341760d = 0x53700
Find a mode in this RTL code section and modify these three parameters,as shown below:
new_hs_div = 3'b100 ;
new_n1 = 4'b1010 ;
fdco = 23'h05_3700 ;
In addition, Silicon Lab also provide the corresponding calculation tool.
Users can refer to the Programmable Oscillator tool (See
mentioned in below link to
calculate the values of new_hs_div and new_n1, then, the fdco value can be calcuted with above
ftdo equation.
http://www.silabs.com/products/clocksoscillators/oscillators/Pages/oscillator-software-development