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TMS570LC4357: Oscillator missed pulses behavior on Hercules microcontroller

Part Number: TMS570LC4357

Hi,

We are feeding a 20MHz oscillator clock to OSCIN input of Hercules micrcontroller.

Can you please let us know what would be the behavior of microcontroller if oscillator misses or generates runt pulses of 100ns pulse duration?

Will the microcontroller generate an oscillator fail if one or two clock cycles from oscillator gets missed?

Regards,

Archana Rao

  • Hi,

    Any update on above request?

    Regards,

    Archana Rao

  • Hello Archana,

    The LPO and clock detect circuit uses the LPO HF to monitor the oscillator inter frequency.

    1. If oscillator misses, the input frequency is out of the valid range (<minimum HF LPO /4), OSCFAIL flag is set in GLBSTAT, the CPU executes the application at a reduced frequency (HF LPO) if ROF is not set. If ROF bit (PLLCTL1.23) is set, the OSC failure will generate a MCU reset.

    2.  The clock signal should be toggling between 0V and 3.3V. How's the runt pulses look like?

  • Hi Wang,

    Thank you for your reply.

    So, even if oscillator misses one clock pulse (and if ROF is not set), does the CPU execute application at reduced frequency? Or is there a certain margin where the output of VCO will be held even if input is missed by one clock cycle?

    Runt pulses would be similar to waveform where the pulses do not cross the required thresholds.

    Regards,

    Archana Rao 

  • Hello Archana,

    One missing clock pulse is certainly not detected. The clock detect circuit works by checking for a rising edge on one clock (oscillator or HF LPO) between rising edges of the other clock. HF LPO is used to monitor the oscillator input frequency.

     

    If more than 4 rising edges of OSC between 2 rising edge of HF LPO are detected, OSC failure is reported.

    If more than 4 rising edge of HF LPO between 2 rising edge of OSC are detected,  OSC fail is generated.