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PMMCOREV settings and SMCLK

Brandon Gardner
Prodigy 220 points
Other Parts Discussed in Thread: MSP430F5529

For the MSP430F5529:

In the PMM datasheet, it states the MCLK frequency range supported by various PMMCOREV settings. Is the required Vcore affected at all by SMCLK?

For example: What if my MCLK was 1 MHz but my SMCLK was 25 MHz? Would I need to use PMMCOREV 3 just like if MCLK was 25 MHz? Or could I use PMMCOREV 0?

I hope I have been clear in my question.

  • 0
    Guru 12160 points

    Brandon,

    The short answer is yes, you'll need to use PMMCOREV 3 even if only SMCLK is 25MHz.  The reason is that presumably you are going to provide that 25MHz to some module inside the MSP430 (like a timer or a USCI etc), and it can't operate with that clock unless PMMCOREV is set to 3.  The data sheets specify maximum clock speeds for these modules, and they usually specify fSYS which is the one based on PMMCOREV.

    Jeff

  • 0 in reply to Jeff Tenney
    Guru 12160 points

    Actually I just double checked and it looks like the Timer module does allow you to go up to 25MHz, even at PMMCOREV 0.

    Also if you want to put SMCLK onto a pin that could be up to 16MHz while still at PMMCOREV 0.

    So I guess the cleanest answer is "it depends" on what you are trying to do with the SMCLK > fSYS.

    Jeff

  • 0
    Guru 34453 points

    I'm working mostly on MSP430F550x DIY USB dev boards (powered by 3.3V internal LDO), with 24 MHz XT2 (used for 24 MHz MCLK), on default core voltage.

    http://e2e.ti.com/support/microcontrollers/msp430/f/166/t/268778.aspx

    I only increase core voltage in case of overclocking.

    http://forum.43oh.com/topic/3906-msp430f5xx-overclocking

    BTW, timer module don't have any problems with default core voltage, and higher clock rates. For example, it is able to capture 48 MHz signal (TA0CLK/TA1CLK on external pins) even MCLK it is running on "only" 24 MHz, with default core voltage.

    http://forum.43oh.com/topic/3317-msp430f550x-based-frequency-meter/?p=35453

  • 0 in reply to Jeff Tenney
    Prodigy 220 points

    Jeff Tenney said:

    Actually I just double checked and it looks like the Timer module does allow you to go up to 25MHz, even at PMMCOREV 0.

    I found in the device datasheet where the max timer frequency is 25MHz, but I don't see where it says anything about PMMCOREV. 

    Jeff Tenney said:

    Also if you want to put SMCLK onto a pin that could be up to 16MHz while still at PMMCOREV 0.

    Where did you find this in the datasheet?

    I want to make sure I can reference these items in my documentation. 

  • 0 in reply to Brandon Gardner
    Guru 12160 points

    Hi Brandon,

    Here's the timer piece of the data sheet:

    I highlighted the 1.8V part -- that's the part that allows you to run with PMMCOREV 0.  Or better said, you cannot use PMMCOREV 1-3 at 1.8V Vcc.

    And here's the DIO output pin frequency part:

    It specifically mentions PMMCOREV 0 and correlates it to Vcc=1.8V as expected.

    Jeff

  • 0 in reply to Jeff Tenney
    Guru 58965 points

    I wish TI would put more effort in making the data-sheets more accurate and clear. Topics like pin schematics in various data-sheets are a mess. And in this case, the frequency limits (other than that of the CPU) at various core voltages are never clearly stated.

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