PWM Frequency

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PWM Frequency

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ock
Contributor II

Hi guys,

Im currently working with the TWR S12G64.

I wanted to use the external Oscillator (8 Mhz) for the Bus clock.

 

CPMUOSC_OSCE = 1

 

CPMUCLKS_PLLSEL = 0

 

Now my bus clock should be 8 Mhz right? Or am i missing anything?

Im grateful for any help

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iggi
NXP Employee
NXP Employee

Hi,

Actually the bus clock depends on how the system clock registers (CPMU) are configured.

For example, from 8MHz ext. oscillator you can get 4MHz bus clock  in PBE mode (PLL Bypassed External Mode).

Or, if PLL Engaged External Mode (PEE) is used, you can set the bus clock up to 32MHz.

More on this in S12G ref. manual and section 10.4.6 System Clock Configurations.

System Clocks SW examples you can find with application note AN4455:
http://cache.freescale.com/files/microcontrollers/doc/app_note/AN4455.pdf

http://cache.freescale.com/files/microcontrollers/doc/app_note/AN4455SW.zip

regards,

iggi

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ock
Contributor II

edit: The S12G64 MCU has 4 Clock options for each PWM channel. Those for Clocks have the bus clock as source (thats why there is PWM frequency in the Title)

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