If a master wants to change the selected slave from slaveA to slaveB, then how to determine the HREADY signal?
should I choose HREADYOUTA to determine HREADY or choose HREADYOUTB to determine HREADY? The picture show as during T4-T5 in purple circle
address A3 is for slaveA marked by blue
address B0 is for slaveB marked by orange
HREADYOUTA is slaveA's HREADYOUT
HREADYOUTB is slaveB's HREADYOUT
HREADY is driven by slaves in that data phase of accesses, so as you are still in the data phase of the A3 access, it is HREADYOUTA that is relevant in the circled cycle T4-T5.
From T5 onwards you are in the data phase of the B0 access, so then HREADYOUTB is the relevant signal driving the master's HREADY input.