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32kHz external clock source

Masa
Intellectual 310 points
Other Parts Discussed in Thread: MSP430G2553

I think that MSP430G2553 supports 32.768Hz oscillator logic input to LFXT1 with the setting of LFXT1Sx=11 & OSCOFF=0.

In this case, I would like to confirm the DC characteristics for clock logic input. Is it the same specification as schmitt-trigger input, port px?

Also, if duty and DC characteristics meets G2553's requirement, can we use not only trapezoidal wave but sinusoidal input as external clock source to LFXT1?

Best regards,
Masa

  • 0
    TI__Genius 10830 points

    "LFXT1Sx Bits 5-4 = 11 Digital external clock source."  I believe this implies a digital square wave input.

    Reference:

    MSP430x2xx Family User's Guide (Rev. I)  (PDF , 4314 KB)   24 Jan 2012 
    5.3.4 BCSCTL3, Basic Clock System Control Register 3

    Would the documentation be more helpful if it could be changed to this?

    "LFXT1Sx Bits 5-4 = 11 Digital external square wave clock source."

  • 0
    Guru 227245 points

    Masa said:
    Also, if duty and DC characteristics meets G2553's requirement, can we use not only trapezoidal wave but sinusoidal input as external clock source to LFXT1?

    Well, this hould work, but due to the not exact trigger point sof the digital circuitry, a definmed DC on a sinusodial wave woudl be a problem. However, if you apply twice the desired frequency and use a /2 divider, you should get an almost perfect 50% DC on the divided frequency.

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