Mark Parzgnat

MPC5554 CPU Clock not what expected

Discussion created by Mark Parzgnat on Apr 28, 2011
Latest reply on Apr 29, 2011 by TomE

I am expecting the CPU Clock to be 15Mhz and my results are 1.5Mhz (details below) and wanted to know if there is any clock dividers (Not RFD) in between the System Clock and the CPU Clock (Core) or am I missing something?

 

The hardware has is a MPC5554 with a 10Mhz crystal set to default with FMPLL_SYNCR (PREDIV = 0, MFD = 2, RFD = 2), which should produce a 15Mhz System Clock.  I execute the following endless loop to strobe a LED and produce a square wave.

 

 while (1)
 {
  
   bClock = ~bClock;
   SIU.GPDO[PIC_PGM_CLK].B.PDO = bClock;
 }

It produces a loop with 10 instructions which I expected to see the square wave :

   High for 667ns

   Low for 667ns

 

And I seeing:

 

   High for 6.48us

   Low for 6.48us

 

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