This thread has been locked.

If you have a related question, please click the "Ask a related question" button in the top right corner. The newly created question will be automatically linked to this question.

MSP430F247: The waveform of XOUT behavior just after releasing the CPU reset

Part Number: MSP430F247

Hi

Product #: MSP430F247TPMR

The following waveform was captured at device power on.

When powering on the device, crystal oscillator (Green waveform) behave  like in the red box (in the waveform below) after releasing the CPU reset (pink waveform).

Q1) What's the reason of the behavior in above red box?

       (Does it affected by the configuration of some register in CPU?)

Q2) Do you think if the behavior in above red box is as expected or not?

Thanks and Best regards,

HaTa.

  • Hi HaTa,

    Thanks for posting to the MSP430 forum. 

    You could be seeing excess capacitance on the XOUT pin. There are a few places in which this could occur:

    - Setting the XCAPx bits in BCSCTL3 register

    - External load capacitance on pin

    - Capacitance from measuring the XOUT waveform on scope probe (not recommended)

    Is this affecting the performance of your system? I would like to omit the idea of crosstalk / layout issues before taking them into consideration. 

    The app note SLAA322D may also help with selecting the right crystal for your application if it's a crystal issue. 

  • Hi Aaron,

    I accidently push the "Resolved" button, but I sill have some questions from customer. Sorry...

    > - External load capacitance on pin

    ==> There is no any load capacitance outside of XOUT pin.

            Is it ok to consider that this item does not apply to us?

    > - Setting the XCAPx bits in BCSCTL3 register

    ==> Yes, we change the configuration of XCAPx.

           However, the behavior of the waveform wasn't changed even if we remove the code where XCAPx is changed.

    > - Capacitance from measuring the XOUT waveform on scope probe (not recommended)

    ==> We feels that it's not caused by this, because the waveform at issue occurs about 500 ms after the reset is released.

    Q1: Is there anything else that can cause it?

    Q2: What kind of harmful effects may occur if the operation is as it is now?

     

    Thanks and Best regards,

    HaTa.

  • Hi HaTa,

    1) If extra capacitance is not causing that, then the only solution I can think of would be board layout and routing. 

    2) It is hard to say depending on the application. Typically if you are using the external crystal and an error occurs, you will see the LFXT1OF set to a 1 for a crystal oscillator fault. 

    Is the behavior affecting the application? Are you measuring the correct frequency on the ACLK pin?

**Attention** This is a public forum