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MCF54450 Clock Speed, PLL Multiplier

Question asked by Kyle Edwards on Feb 27, 2013
Latest reply on Feb 28, 2013 by Kyle Edwards

Hello everyone,

 

I'm working with a MCF54450 processor running U-Boot 2013.01.01, trying to bring the clock speed down from 240 MHz to 180 MHz. The processor is running off of a 24 MHz crystal. It's running in serial boot mode, and our 7-byte SBF header is as follows:

 

0E FF 0F 00 00 14 C0

 

I've attempted to change the clock speed by changing the PLL multiplier from 0x14 to 0x0F. However, when I do this, the processor doesn't print anything to the UART console, and doesn't seem to boot at all. In fact, the lowest clock speed I've been able to achieve is 204 MHz, by changing the PLL multiplier to 0x11. Anything lower than this and the processor doesn't boot.

 

Is there another setting I need to change to get the clock speed down to 180 MHz and still have it boot properly? Perhaps some RAM timing setting that needs to be changed? Thanks in advance.

 

Kyle

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