DS90UB926Q-Q1: timing requirement for accessing registers

Dear TI Experts,

1. When DS90UB926 is powered up,Is there a timing requirement for accessing registers through I2C?

Must we  access registers after the Lock signal?

2. Soc--->927<- ----- ->926<- --- MCU

If Soc access the register of 926 by control 927, at the same time , mcu is accessing 926 too, Is there a problem