Arduino due erase button and power switching

Question

Last days I have been investigatin schematics of arduino due board. The purpose of proper understanding of schematics in crucial for me, beacuse I indend to build myself my own board with some minor modifications.

I would really want to learn something from it and not just blindly copy stuff that are already done. In schematics there are two things that I do not understand. First is the working principle of erase button (see: erase button). I have my own idea how does it work, but would like to clarify the working principle from someone that know exactly what is the purpose of all the elements that are connected to erase button. Also, why is ERASE_CMD line connected to Atmega processor? Second thing is switching of power supply between external power and both usbs (see: usb switch). Again, would someone please just brifly describe working principle? Here I really do not undertand why is there op amp added?

Thank you in advance.

Erase button:

enter image description here

USB switch: enter image description here

PLEASE NOTE: Both pictures are taken from original arduino webpage: https://store.arduino.cc/due (see: documentation -> schematics)

Answer 1

The asker posted the same question and received an answer here There is discussion regarding the purpose of the Erase switch here

• timemage: You're encouraged to summarize the essentials such that the answer will remain useful if the links become broken.