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MSP430F67751A: clock configuration

subramani pasupathy
Intellectual 575 points

Part Number: MSP430F67751A

Hi All,

Can we generate accurate 16Mhz MCLK clock with a 32.768Khz HCMOS TCXO for MSP430F67751A

Does anyone have the register values calculator for quick calculation for it to set up the MCLK

I think the XT1BYPASS to be set to 1 for oscillator input on XIN pin.

What will happen if XT1BYPASS to be set to 0

regards

Subbu

  • 0
    TI__Intellectual 1330 points

    Hi Subbu,
    I would propose you to use a HF crystal to generate an accurate 16 MHz clock. We collected a lot of code examples which you can reuse, please find the package with the following link. The files named with UCS are the ones for the clock system.

    http://www.ti.com/lit/zip/slac648

    About the XT1BYPASS bit, when the XT is in bypass mode, the XTCLK can be driven with an external square wave signal. This means that you do not need a crystal. So in your case, you have to turn it of (set to 0).

    Best regards,

    Tobias

  • 0 in reply to Tobias Oschmann
    Intellectual 575 points
    Hi Tobias,

    Thanks.

    The datasheet of MSP430F67751A 5.7.2 Clock Specifications, table 5-2 is for LF mode. I could not see HF mode in the data sheet. But in user manual it is given. Not sure if MSP430F67751A can be driven by external high frequency crystal or oscillator.
    Kindly guide me in identifying HF mode in the datasheet

    Appreciate your help

    regards
    Subbu
  • 0 in reply to subramani pasupathy
    TI__Intellectual 1330 points
    Hi Subbu,
    you're right, F67751A doesn't have HF-mode. The manuel is written for the whole device family, that's why it is mentioned there. But datasheet says that there is for this specific device only a LF mode available.

    The DCO performance is not sufficent for your application?

    Best regards,
    Tobias
  • 0 in reply to Tobias Oschmann
    Intellectual 575 points
    Hi Tobias,

    We are using 32.768 TCXO and used it as crystal (ie XT1BYPASS is off and XT is not bypassed). We used DCO and derived 16MHz. This clock is being used for UART and Timer. we got good results. After reading datasheet we have put the XT in bypass mode. (TXCO giving square wave and hence XT is bypassed). Then we are finding timing issue. The timer is not producing good precision of 10ms interrupt.

    Then we configured ACLK to be 32.768KHz without using DCO and used that ACLK to clock the timer. We are getting precise 10ms interrupt.

    The issue now is our UART works at 115200 bps. This baud rate cannot be achieved using ACLK. So we will have to use DCO to multiply and then use MCLK for the UART clock.

    The question that I am wondering is, why the TCXO external clock source and when XT is not bypassed actually worked good.

    We are further doing some more experiments to study the behavior and will let you know tomorrow

    Thanks
    regards
    Subbu

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