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Other Parts Discussed in Thread: MSP430F67451

Part number: MSP430F67451
Ref document: SLAS815C.PDF

We have applied an exteral 24 MHz clock source, with XT1BYPASS = 1, and it works. However, we find
no support for this idea in the above-referenced datasheet. Is our present practice a reasonable choice?

Our reason for use of a high-frequency external clock source is that we find lower timing jitter as a
result. We are applying the SD24B ADC in this system, and we observe better data quality with
our choice as opposed to use of the large multiplication factor with a 32.768 KHz crystal.

  • Hello Mike,

    MSP430 microcontrollers are designed, characterized and tested to run within the specifications outlined in the respective datasheets. Operating above Recommended Maximum values or below recommended minimum values in general could lead to unexpected results; operating above Absolute Maximum values or below absolute minimum values in the datasheet can cause physical damage to the MSP430 MCU.

    It is true that in some use-cases an MSP430 MCU may operate correctly outside of the specified limits, but performance is not guaranteed and such operations are done at the risk of the user and are not recommended by TI.

    Specifically, the part you link only has a LF mode available for the XT1 oscillator even in bypass mode. The max frequency given given in the datasheet for that mode is 50kHz as a square wave input frequency. Please see note sin datasheet for additional information.

  • Hi Jace, and thanks for your response. The notes section of the datasheet for the MSP430F67451, page 67, note 2, says: "When XT1BYPASS is set, XT1 circuits are automatically powered down. Input signal is a digital square wave with parametrics defined in the Schmitt-trigger Inputs section of this data sheet." This doesn't seem to contain a frequency restriction, so if it is correct, then it seems at odds with the 50KHz LF mode speed limitation that you mention. As I mentioned, this internal issue in the documentation is a reason why we've raised this question. As I said, we've built dozens of our prototypes, and all operate flawlessly with a 24 MHz clock signal applied at Xin.
  • Hello Mike,

    As stated above, if you operate the device out of specification given in the datasheet, TI can not guarantee the performance of the device. For this particular device, XT1 is only spec'd and tested for Low-Frequency Mode. The far right column of the table that describes frequency specifications while in L-F mode with a max limit of 50kHz.