CCS/MSP-EXP430G2: Sourcing SMCLK and MCLK from BasiC Clock System causing waveform abnormality. What am I doing wrong?

Part Number:MSP-EXP430G2

Tool/software: Code Composer Studio

Hi all,

I have been trying to source SMCLK and MCLK from the DCO, with dividers in a MSP430G2553 launchpad. The code is as below. The following function is the only content of the program, in main. I have commented all of the rest out.

void basic_clock_system_init_125khz_mclk_smclk_aclk(void)
{
    DCOCTL = 0;                                   // Select lowest DCOx and MODx settings
    BCSCTL1 = CALBC1_1MHZ;                        // Set range
    DCOCTL = CALDCO_1MHZ;                         // Set DCO step + modulation */

    BCSCTL2 |= SELS | DIVS_3 |  SELM_0  | DIVM_3; // SMCLK & MCLK /8

    P1DIR |= BIT4;
    P1SEL |= BIT4;
    // Summary: 125kHz MCLK SMCLK
}

The waveform I observed in the oscilloscope is quite inaccurate. Please see below, the yellow plot.

If I take the dividers off, and just set the SELS and SELM_0, I still get an inaccurate waveform. Please see below.

NOTE: The moment I remove the line "BCSCTL2 |= SELS | DIVS_3 | SELM_0 | DIVM_3;", I am able to get a decently accurate 1MHz waveform. However, as I am trying to source 125kHz (1MHz / 8) on MCLK and SMCLK, i need that line.

Could someone point out what i am doing wrong please?

Thank you.

Kind regards,

Guyan