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MSP 432 I2C baudrate

Shai Gigi
Intellectual 440 points

Hi.

I'm using the MSP432 launchpad with the external HF 48MHz crystal,

The SMCLK is initialize to 1/2 the system clock , which is 48MHz. i check the on the external pin and measured SMCLK-24MHz.

but when i'm using the I2C devider by 60:

UCB3BRW = 0x3C;

the SCLK is measured to be 328Khz instead of 400KHz...

what could be wrong? 

  • 0
    Guru 74080 points
    Hi Shai!

    Is UCSWRST set in UCB3CTLW0 while setting the bit rate control register?

    Dennis
  • 0 in reply to Dennis Eichmann
    Intellectual 440 points
    Yes, I'm setting the bit before all initiations to the I2C registers and then clearing it. all other initiations are preformed correctly.

    NVIC->ISER[0] = 1 << ((EUSCIB3_IRQn) & 31); // Enable eUSCIB3 interrupt in NVIC module
    // Configure USCI_B3 for I2C3 mode
    UCB3CTLW0 |= UCSWRST; // Software reset enabled
    MAP_I2C_enableInterrupt(EUSCI_B3_BASE, EUSCI_B_I2C_BYTE_COUNTER_INTERRUPT);
    UCB3CTLW0 |= UCMODE_3 | UCMST | UCSYNC | EUSCI_B_CTLW0_SSEL__SMCLK; // I2C mode, Master mode, SMCLK, sync
    UCB3CTLW1 |= UCASTP_2; // Automatic stop generated
    UCB3BRW = (US)(SMClock / I2C1BaudRate); // baudrate divider = SMCLK / I2C1BaudRate

    UCB3TBCNT = 0x0002; // number of bytes to be received

    MAP_Interrupt_setPriority(INT_EUSCIB3, I2C3_PR);

    UCB3I2CSA = 0x64;
    UCB3CTLW0 &= ~UCSWRST;
    UCB3IE |= UCRXIE | UCNACKIE | UCTXIE0| UCBCNTIE; // enable RX, TX interrupts
  • 0 in reply to Dennis Eichmann
    Intellectual 440 points
    Anybody knows why the I2C baudrate isn't working correctly?

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