I’m using the NXP FRDM-K64F board in several projects.One issue I have faced several times is that the board works fine while debugging and connected and powered by a host machine, but does not startup sometimes if powered by a battery or started without a debugger attached. I have found that the EzPort on the microcontroller is causing startup issues.
The EzPort is a special serial interface present on some Kinetis, ColdFire+ and ColdFire V2 devices.
The issue is that if the EzPort chip select (EZP_CS) is LOW during reset of the microcontroller, it enters the special EzPort mode. The problem is that a pull-up on the EZP_CS line might not pulled up fast enough due capacitance on the line.
The commance is if something is not used, disable it! So the solution is to disable the EzPort functionality. That setting is part of the FOPT (flash option register).