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Unified Clock System and XCAP

Carloalberto Torghele
Intellectual 835 points
Other Parts Discussed in Thread: MSP430F5505

Hi!

I'm using a MSP430F5505 with a 32768 Hz quartz on XT1.

I want to use 2 external load capacitors instead of selecting internal capacitors with XCAP.

Therefore I would clear XTS in UCSCTL6. Is it correct?

What it's not clear to me is if XTS is involved with other stuff or if its only function is to enable/disable internal capacitors. Could anyone clarify this?

Will the power consumption rise selecting XTS?

Best Regards,

Carloalberto Torghele

  • 0
    Guru 227245 points

    XTS switches the oscillator circuit between LF and HF mode. You need LF mode for a 32768Hz crystal. In HF mode the internal silicon capacitors are implicitely disabled. So this is a side-effect and not the primary purpose of XTS.
    In LF mode, you can chose to use them or not by selecting the capacitance with the XCAP bits. You cannot disable the parasitic pin capacitance, so clearing the XCAPx bits (setting XCAP_0 won't clear any bit, as it would be an OR with 0x00) will result in 2pF pin capacitance on each XT1 pin and you can use your external capacitors.

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