I want to write programs for MKE02Z64LVD4 microcontroller. Tell me which compiler should i use for this?VD$
You can use MCUXpresso, KDS, CW10.x, Atollic, S32 Development Studio or Rowley Crossworks, which all use the GCC compiler.
Or you can use IAR or uVision or Green Hills (and probably various other less known ones).
If you only consider free tools then your choice will be one of the GCC based ones.
When i go to download MCUXpresso, it asks me for serial no. From where i get it?
I know of no serial number (unless it has been added since I downloaded it). You will need to ask NXP what it is - if possible you can ignore it because I don't think you need to do anything special.
Otherwise use KDS since it is more or less the same (at the moment) although I expect NXP will drop support of older tools and invest only in MCUXpresso in the future (until it gets replaced by whatever follows).
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