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External clock input frequency range of MSP430F6?

Zhiyong Li
Prodigy 180 points
Other Parts Discussed in Thread: MSP430F6720

Hi,

I am trying to use MSP430F6720 to measure the frequency of a input signal, the way I plan to do it is: feed signal onto TACLK pin, and set another timer to measure time duration.

My question is: what is the frequency range TACLK pin can take? I am particularly interested in the upper range. I could not find this information in datasheet. So please advise.

Thanks a lot.

ZL

  • 0
    Mastermind 7565 points

    if you will be use CCRx  capture mode

    first you should see on maximum Timer clock frequency !

    input signal frequency measure is always connected with timer clock frequency

    in my opinion 1-2 MHz will be max,

    it depends on how fast will be you code ( TimerA interrupt routine and frequency calculation )

  • 0
    Guru 33653 points

    I done the same thing with MSP430F550x  (running on 24 MHz MCLK XT2) and it was able to measure 48 MHz. Didn't try to measure value higher than this, so don't know exactly about upper limit.

    http://forum.43oh.com/topic/3317-msp430f550x-based-frequency-meter

  • 0 in reply to zrno soli
    Mastermind 7565 points

    zrno soli said:

    I done the same thing with MSP430F550x  (running on 24 MHz MCLK XT2) and it was able to measure 48 MHz. Didn't try to measure value higher than this, so don't know exactly about upper limit.

    http://forum.43oh.com/topic/3317-msp430f550x-based-frequency-meter

    ok in this configuration it is possible,

  • 0 in reply to zrno soli
    Prodigy 180 points

    zrno soli said:

    I done the same thing with MSP430F550x  (running on 24 MHz MCLK XT2) and it was able to measure 48 MHz. Didn't try to measure value higher than this, so don't know exactly about upper limit.

    http://forum.43oh.com/topic/3317-msp430f550x-based-frequency-meter

    That's very assuring. The signal I am dealing with is at most 15MHz, so I guess it should be a problem. According to a post on 430oh, maximum external frequency for TACLK is actually specified for MSP430F550x, odd I cannot find this in F6 series datasheet.

    Edit: I just found the range for F6, it is the same, max 25MHz.

    A further question would be: does this maximum frequency depend on frequency of MCLK? I'd like to set MCLK as low as possible to reduce power consumption.

    Thanks.

  • 0 in reply to Zhiyong Li
    Guru 227245 points

    For any kind of frequency metering, you’ll need a known reference clock. (time is relative)

    There are two methods to measure a frequency. It depends on whether the frequency you’re testing is (much) higher or lower than your reference clock.

    If the frequency you measure is high, you can count the number of ticks for a known period. E.g. if you have a frequency of, say, ~1MHz, you can count the number of clock pulses per 244µs and get a 244Hz resolution. In this case, you would feed the signal into the timer (TACLKIN) and trigger a capture by the reference. (in this case assuming a trigger by ACLK, sourced from 32768kHz crystal/8)
    If the frequency you measure is slow compared to the reference, you let the timer count the reference pulses (e.g. 8MHz from DCO) and trigger a capture by the signal, getting the number of reference pulses per signal pulse. If the signal is fed to TA0CLKIN as well as a CCR input, then you can switch both methods at runtime, depending on the results of the other method, automatically picking the best.

     The maximum input frequency does not depends on MCLK. But it depends on VCC. The 25MHz are assured even for the lowest VCC allowed, while on higher VCC, higher frequencies are possible, but not specified/guaranteed (the digital logic runs on VCC, and since it is CMOS logic, its maximum speed depends on supply voltage).

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