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MSP430F248: XT2 range selection of register BCSCTL3 not match with User Manual and driver library, also affect power consumption .

Vincent Hu
Prodigy 230 points

Part Number: MSP430F248

Hello Sir,

We used TI MCU MSP430F248 and found some issue of this chip initializaiton.

1)  The board we designed used 3.6864MHz oscillator, so of course we set register BCSCTL3 : Bits 7-6(XT2 range select)  : 10    3-to 16-MHz crystal or resonator

2)  MSP430F248 head file in IAR , its comments seems has some conflict with User Manual ( But I think this definition in User Manual should be right )

3)  Anyway,  my question is : when we selected "XT2S_2" configuration after power on and run the whole system , its power consumption = 2.6mA

                                               when we not set this Bits7-6 (default setting after power on should be 00 ), its power consumption = 1.6mA

                                               when we selected "01" (1- to 3-MHz crystal or resonator ), its power consumption about 1.6mA .

But the actual external crystal = 3.6864MHz , so would you mind help us to analyze why cause this abnormal issue?

Hope your response ASAP.

Thanks.

Best Regards,

Vincent

  • 0
    TI__Guru 56685 points

    Hello Vincent,

    When looking at application notes, user guides, example software, or even header files, it is important to keep in  mind the scope of these documents. Typically, these type of collateral are written for more than one device, and in fact whole families of devices. Also, sometimes the document is based off the first device in the family, and has not been updated to reflect different values in potentially "newer" device sin the family. this is especially true in such a diverse family as the MSP430x2xx family of MSP430 MCUs.  This means, sometimes you will see discrepancies as you pointed out. When this happens, the device specific Datasheet is the highest authority for the device.

     


    for your device, the MSP430F248, you can see in section Crystal Oscillator XT2, the different frequency ranges the different modes cover (XTSx setting). For this particular device, Mode 1 can cover a range of 1-4 MHz, while mode two can cover 2-16 MHz depending on voltage. This means with your XT2 frequency of 3.6864MHz, you could use either mode 1 or 2.

    Now, the different modes will correspond with different drive strengths for the Xtal with generally the higher the mode, the greater the drive strength. This increased drive strength translates to more current. So I'm not surprised you see a big current difference between the two modes. For your setup, I would recommend using mode 1. 

  • 0 in reply to Jace H
    Prodigy 230 points
    Hi JH,

    Thanks for your response.

    BTW: I also downloaded the latest datasheet and user manual of MSP430F248. But I still did not find the description of register BCSCTL3 about mode 1 ( 1 to 4 MHz ) and mode 2 (2-16 MHz).

    Which official document describe this information correct ? Or would you mind give me a link to download it ?
    Thanks for your understanding.


    Thanks.

    Best Regards,
    Vincent
  • 0 in reply to Vincent Hu
    TI__Guru 56685 points

    Hello Vincent,

    As mentioned earlier, it is in the section/table Crystal Oscillator XT2 in the datasheet. Page 51 in the current revision. I've included a snippet below.

  • 0 in reply to Jace H
    Prodigy 230 points

    Hi JH,

    Thanks a lot for your information.

    Best Regards,

    Vincent

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