I have a 4MHz external crystal and want the CPUCLOCK = 32MHz and BUSCLOCK = 16MHz so both the SCI and RTC can use the bus clock for timing.
Which CPU model, exactly.
I've got the MCF51EM256 manual open, and a search for "MCG" (which means "Melbourne Cricket Ground" to me :-) doesn't find anything.
If you've tried to program it and are having trouble, post a section of your code and what you're measuring.
Thanks for responding to my question.
Given the following:
Desired Reference clock: 4MHz external crystal
When set correctly, the CPU clock frequency will be 32MHz and the BUS clock will be 16MHz.
My question is this
I believe I need to change the clock settings from FEI mode which uses the internal reference clock;
To FEE mode which uses the external crystal oscillator.
Please tell me what values to load into the MCG module registers:
MCGC1, MCGC2, MCGC3, MCGC4, etc. and
Please tell me the sequence, ie: which register to load: 1st, 2nd, 3rd, etc.
Also indicate if I need to read, write, or pause until certain bits are set in the MCGSC ( Status / Control ).
Lastly, tell me what effect my debugging using the PE Micro BDM interface will have on these clock
Thankyou for your help ! Have a super day !
Bob Reichenbach email@example.com
Minimus Spine, Inc.
Austin, TX. 78750
Here's a snippet from an old JM128 project of mine:
// Clock generator setup - external 12 MHz reference crystal, 48 MHz PLL// MCGOUT must be 48 MHz for USB operation (PLL engaged external)// 12 MHz / 8 = 1.5 MHz, * 32 = 48 MHzMCGC2 = 0x36; // High range, high gain, osc on, MCGERCLK active, BDIV=1while ((MCGSC & 2) == 0);MCGC1 = 0b10011000; // External reference, RDIV=8while ((MCGSC & 0x10) != 0);while ((MCGSC & 0x0c) != 0x08);MCGC3 = 0x48; // PLL selected, VDIV=32while ((MCGSC & 0x20) == 0);while ((MCGSC & 0x40) == 0);MCGC1 = 0b00011000; // Switch to PLL, RDIV=8
This was set up for a 12 MHz reference crystal and produces a 48 MHz bus clock, so it should give you your 16 MHz bus clock from 4 MHz.
If you're using CodeWarrior, I'd suggest checking the Processor Expert tool. It does a pretty good job on ColdFire. Even if you don't want to use PE in your project, you can create a dummy project and use the clock configuration tool to generate code you can reference.
I've got a couple of P&E Cyclone PROs and a couple of Multilink BDMs and they haven't needed any special setup.
Hope that helps,
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