[Discuss-gnuradio] DDC block diagram confuse

[Wipat phonsukkarn]

I'm new for gnuradio and usrp but I tried to use two of them for the digital beacon receiver. So i tried to understand most of the block diagram in usrp
and now i have  detail of the usrp from many site. One is the USRP user's and Developer 's Guide(Matt Ettus) and The USRP under 1.5X Magnifying Lens!
And i saw the difference in the DDC block diagram between two of this sheet that is from first sheet they said after nco the signal will be pass trough the Decimating Lowpass filter (Bandwidth decimation factor = N) but from the second sheet they said after the nco the signal will be pass through the 4 stage CIC Decimator and 31 Tap HBF divide by 2.

so that make newbies like me confuse what difference between CIC+HBF(confused) and Decimating LPF(this one i understand)

and from the 1.5X mag.. i saw the question that asked about mux and i interested It said that
If i want to generate the signal 1.5Mhz from signal generator connect to the BasicRx DB directly How todo ?

and the answer was said that Just connect to the input connector and use 0xf0f0f0f0 setting for the MUX that mean feed zero into each DDC Q inputs and ADC0 into the DDCI

from this answer what i confuse is from 0xf0f0f0f0 i understand it's arrange f0 f0 f0 f0 = Q3 I3 Q2 I2 Q1 I1 Q0 I0 that I correct and how did they know that they are connect ADC0(because they have 4 ADC(0,1,2,3)) to the DDCI

and i if i set mux = 0x00002201 what does it mean for more detail please if i have BasicRx(sideB) board and WBX DB(sideA)

Thank you so much for every advice
I need this information for clear to do my project(Now i'm only thai undergraduate student that work in GNURADIO so nobody can help me!!! )

Wipat