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How can I boot to LPC55 to BOOT ROM from firmware code?  Previous method doesn't work

Question asked by Conor Patrick on Apr 26, 2020
Latest reply on Jun 1, 2020 by Diego Charles

I'm trying to get the LPC55 to enter the bootloader from application code.  I previously tried this solution which edits the `BOOTERRORCOUNTER` of the AOREG1 register.  This solution did work on my LPCXpresso55S69, but it does not work on my custom PCB with new LPC55 chips.

 

On the LPCXpresso (device revision marked "1"), it works and boots to BOOT ROM just fine.

 

On custom PCB (chip revision marked "1B"), it just boots the application again. 

 

In both cases I confirmed that BOOT ROM works/boots after mass erasing the flash.  I also figured out I could erase the first flash page from application code and reset, which results in BOOT ROM booting, but this is problematic since now the application needs to be reprogrammed.

 

Would there be a difference between chip revisions in how the boot rom handles `BOOTERRORCOUNTER` in AOREG1 register?  How else can I boot the BOOT ROM from application code (without erasing application)?

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