how to enter Bootloader mode

[Chaw]

Hi, Nordic

I check this: devzone.nordicsemi.com/.../ , first, it will work when I follow this article. Then I have 2 questions:

1. it said "If the bootloader LED is not lit, try pressing Button 4 during startup, this will put the device into bootloader mode".
   where can I found these code? (press button 4 to enter to bootloader mode)

   If I want to change the way to enter bootloader mode, how can I do?

   after DFU done, when I download new bootloader, it show "ERROR: The area to write is not erased.", this time, if I want to update bootloader, only can DFU?

2. I check, when DFU done, bootloader->app, now APP is running, can I add code to make nRF52 enter to bootloader mode? If yes, how can I do?

Plz help me. Thanks.

[Chaw]

Hello, for other issues, could you explain? where can I found these code? (press button 4 to enter to bootloader mode)