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MCF52259 I2C I2FDR Incorrect clock frequency

Question asked by William Hookway on Sep 30, 2011
Latest reply on Oct 5, 2011 by William Hookway

Hi,

 

I am using the I2C interface and have a strange clock frequency problem.  My system oscillator is 24 Mhz with a predivide (CCHR=2) divide by 3, and a PLL multiply by 8 for a system clock frequency of 64 Mhz.

 

Setting the I2FDR register with 0x0d (divide by 160) results in a slightly slow clock frequency of 381 KHz.  If I use the 0x30 (also divide by 160) I get the correct frequency of 400KHz.  Trying other values from the 2nd or 4th column of the I2FDR work as expected, but selecting the same divider from columns 1 and 3 result in a slightly slow frequency.

 

I cannot find any information on what the individual bits of the I2FDR register do.  Why are there multiple frequency dividers?

Any help would be appreciated.

 

Thanks,

Will

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