ADF5904 readback vs temrature to ATEST

In it's regiter we can see in Register2 "Channel TEST select" we can set it to "Temrature to ATEST" or set it to some register readback.

1.It meant reading temperature from ATEST and readback from DOUT is not possible at the same time. Am I right? Then why ATEST is not continually connected to Temprature node or at least why we can't set it to 3State? Also what will be readingback from ATEST?

2. Selecting each channel and LO path from Regiter1 is necessary only if temperature changes more than maybe 10 degree. Am I right? Maybe they setting them will cause calibration, since there is no explanation about them!!!

Qestion extended more
[edited by: mohammadsdtmnd at 8:37 PM (GMT 0) on 7 Dec 2019]