Boot Loader Issue

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Boot Loader Issue

Contributor I

We are using LPC54628J512ET180 in some of our product. We are recently facing an issue about boot loading. We are keeping ISP0, ISP1 and ISP2 pins floating in our design , similar to the reference design of your SDK board. We have provided just push button switches tied to ground, to select boot modes, hence there is no provision to pull up them (this provision is also not found in your reference designs). We are facing the issue in boot loading the internal Flash of MCU. In some hardware the boot loader is unable to boot up the MCU from Internal Flash. We need to provide external pull up on hardware to get it booted up from internal flash. But this is not mentioned in your reference designs. So we would like to know, if the external pull up are really required or not ? or these pins are internally pooled up by default ?

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NXP Employee
NXP Employee


Unfortunately, the pullup resistors are required, not in all designs since it really depends on the way the PCB gets done.  My advise it is that you make sure to secure the 1 and 0 of the Boot pins, to assure the proper state.  I understand that our design does not use it, but it is because we only use one of the multiple options that we have, and even if the pull-up required, I  strongly suggest that you keep the pull-up.Even just leave it DNP, (do not populate if this is case) but if you are planning to have multiple options, then keep the resistors available.

Have a great day,

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