dear dun han you wrote I had NOT enabled MAM before. I enabled it and the system works correctly now. Thank you for your useful advices.
same problem we have our led is 2-3 mhz.and we know we must see 30 mhz around.
which is correct about pll and MAM?
Also LPC214x has a Fast GPIO Interface which should be used in order to achieve the best performance. The interface is enabled in SCS register and uses similar registers like legacy GPIO. Details are in the User Manual.
Frequencies up to 15MHz can be achieved with proper code (CPU @ 60MHz).
Me bad. Yes, the LPC21xx can select between legacy and fast accessing modes for the two ports but will default to the legacy access mode.
i will look to SCS registers.thanks robert rostohar