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Questions regarding power and clock of MSP430f5232.

Jason Kang
Intellectual 470 points
Other Parts Discussed in Thread: MSP430F5232

Hi, 

I have several questions on the power and clock of MSP430F5232. 

  1. I could not find a reference design with MSP430F5232. Is there a reference design? I want to check how clocks and powers are provided in the reference design.  
  2. Power: For MSP430F5232, all three powers VCC/AVcc/DVcc are tied together with two capacitors of 10uF and 0.1uF according to the reference design in the user manual (p.21/153 of SLAU278p). Is it a recommended power circuit design?
  3. Power: I want to estimate the maximum power of the MSP430F5232. According to the table on page 46/104 of "SLAS897-Sept 2013", power can be estimated depending on its frequency when the Vcc is 3.0V. By the way, I am planning to use 3.3V of Vcc. In that case, is there a way of estimating its maximum power? Or is the power going to be very similar to the values shown in the table? 
  4. Clock: Is it necessary to place an external crystal to provide a clock? Or can I use only internal VLO to make uC work?
  5. Clock:The manual says that XT1 is up to 32kHz while XT2 is up to 32MHz. Is it necessary to provide both XT1 & XT2?
  6. Clock: If it is required, what frequency is to be used for XT1 & XT2? In other words, what value can be selected? Can I randomly choose any value as long as the value is less than the maximum (XT1 (up to 32kHz) & XT2 (up to 32MHz))?

Thank you in advance. 

  • 0
    Intellectual 470 points

    Maybe, there are too many questions for this thread. 

    Let me split the above questions into several threads. 

    Thank you. 

  • 0
    TI__Intellectual 1310 points

    Hi Jason,

    Please disregard my post in your other thread, I will answer your clock questions here. I answered your power questions in the other post, please see that thread for responses to 2 & 3.

    Jason Kang said:

    Clock: Is it necessary to place an external crystal to provide a clock? Or can I use only internal VLO to make uC work?

    It is not necessary, you can use the VLO. An external crystal would provide a more stable reference, but it is up to you to determine what your requirements dictate.

    Jason Kang said:

    Clock:The manual says that XT1 is up to 32kHz while XT2 is up to 32MHz. Is it necessary to provide both XT1 & XT2?

    There is not a strict requirement to use any external crystals or oscillators.

    Jason Kang said:

    Clock: If it is required, what frequency is to be used for XT1 & XT2? In other words, what value can be selected? Can I randomly choose any value as long as the value is less than the maximum (XT1 (up to 32kHz) & XT2 (up to 32MHz))?

    First of all, it is not strictly required.

    XT1, if using a crystal, should be 32768 Hz (this is a standard LF crystal frequency).

    XT2, if using a crystal, has a range of possible values. You want to choose a crystal based on what your desired system clock frequency will be, i.e. if you plan to run at 20MHz, use a 20MHz crystal. Please see page 53 of the MSP430F5232 datasheet for this information. Keep in mind that power consumption increases with increasing MCLK frequency.

    Thanks,

    Ian

  • 0 in reply to Ian Cathey
    TI__Genius 10405 points

    Hi Jason,

     

      In addition to VLO, you should note that this MCU has a second internal clock source REFOCLK.  Many customers use the internal REFOCLK, which is 32KHz.  

     

    Please note that VLOCLK has a very wide tolerance, and is not too accurate: (6KHz to 14KHz).

     You might need an external crystal clock source, if you need a high speed UART interface, for example.

     

      Best,

          Rick Nardone

  • 0 in reply to Ian Cathey
    Guru 46710 points

    Ian Cathey said:
    XT1, if using a crystal, should be 32768 Hz (this is a standard LF crystal frequency).

    Actually you are not limited to 32768 Hz which without doubt is most common frequency. Crystals for other, 20..100 KHz-range frequencies are rare but they happen to exist and LF XT1 supposedly will work with them.

  • 0 in reply to Rick Nardone
    Intellectual 470 points

    Thank you for your valuable feedback.

    By the way, I have another quick question.

    If I use both I2C master and SPI master, can I run these signals with a low speed clock? - for example, "9.4kHz from VLO" or "30kHz from XT1 or REFOCLK" .

    The spec shows the maximum clock speed (400kHz for I2C & system clock for SPI). 

    But, I am not sure if these protocols will run with the lower-speed clocks which are already available in the MSP430xx.

    Thank you. 

  • 0 in reply to Jason Kang
    TI__Intellectual 1310 points

    Jason,

    Yes, you can elect to source the SPI and  I2C clocks (based on the BRCLK in the USCI peripheral) from ACLK instead of MCLK. ACLK is sourced from either XT1 or VLO.

    However, you can also configure the SPI and I2C clocks to run slower than MCLK by using the clock dividers which are in the USCI control registers; you are not required to run at "full speed".

    Thanks,

    Ian

  • 0 in reply to Ian Cathey
    Intellectual 470 points

    Ian.

    Thank you for your feedback. 

  • 0 in reply to Rick Nardone
    Intellectual 470 points

    Hi, Rick. 

    You mentioned that VLOCLK is not very accurate.

    I have two questions.

    1. Can the VLO be configured at a certain value between 6kHz & 14kHz? 
    2. If the frequency can be configured, are you indicating that the actual frequency will still vary a lot even though it is set to a certain value?

    Thank you. 

  • 0 in reply to Jason Kang
    TI__Genius 10405 points

    Hi Jason,

       Unfortunately, the VLO is not configurable or trimmable on this MCU.  The spec from the data sheet is:

     

       You will be much better off using REFOCLK, if you choose not to use an external crystal.   The VLO is useful in certain situations, but you have to understand its limitations.

        Best,

            Rick

  • 0 in reply to Rick Nardone
    Intellectual 470 points

    This is what I need to know.

    Thank you so much. 

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