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MSP430FR2633: The use of external crystals issue

Part Number: MSP430FR2633

The customer intends to improve the accuracy of the system clock by switching from an internal DCO to an external clock.

The customer would like to know the following info:

1. Can the MSP430FR2633 only use a 32768 crystal?

2. If the customer intends to configure the MCLK and SMCLK to 8 M/2M, can he only use the DCO and select the reference source for the FLL when configuring?

       CSCTL3 |= SELREF__REFOCLK;              // Set REFO as FLL reference source 

OR  CSCTL3 |= SELREF__XT1CLK;               // Set XT1CLK as FLL reference source

Thanks!

Best Regards,

Cherry Zhou

  • Hello Cherry,

    Yes, the customer can connect a 32KHz crystal to improve the DCO accuracy.  There is also an internal 32KHz REFO oscillator that can be use, but consumes ~15uA compared to an external 32KHz which consumes ~ 1uA.  So depending which 32KHz source the customer wishes to use, yes, the code snippet would select the appropriate clock source.  Note, if using the XT1 source, the customer must also configure the corresponding GPIO pins for driving the XIN and XOUT signals using the P2SEL register:

    P2SEL0 =  (GPIO_PIN0 | GPIO_PIN1);

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