What needs to pay attention on the circuit design when selecting boot from Internal SPI Flash mode in NUC505?

[a_ziliu]

The NUC505 is designed to set the booting mode according to the four pins, PB.4, PB.3, PA.10, and PA.9, as shown in the table below:

When using Boot from SPI Flash mode, if the PA.9 status is low (i.e. Boot from USB) before power-on, the code may be cleared.
It is suggested that a pull-up resistor is reserved outside the four pins to adjust the pin status.

When the NUC505 boots, there is a 47k internal pull-up resistor in the four pins. If the current sink of the chip is too strong, it may lead to abnormal pin status. Thus, it is recommended to add the pull-up resistor to the four pins to adjust the pin status.