UART connection problem on MSP430F5529 LP

After establishing communication over UART (UCA0) with Beagle Bone Black at baud rate of 9600,

We are trying to make this communication happen at faster rate.

wanted to increase baud to its maximum 460800. As an intermediate step we are increasing it to 115200, and then to 230400. Please find commented part showing settings for these baud rates. 

1. Clock source chosen  is SMCLK (running at 8MHz).

     When I scoped this clock on pin 2.2, SMCLK is observed to be varying from 7.947 MHz to 8.469 MHz.

     Will this affect baud rate or robustness of data reading ? because for same baud rate UCBRx values are different for 8.0 MHz and 8.388 MHz.  

2.  No oversampling enabled.

3. Modulation types are as per TI guidelines.

4. UCA0BR0 and UCA0BR1 values are as per TI guidelines.

CODE :

#define BAUD_460800_WITH_SMCLK_8M 17

#define BAUD_230400_WITH_SMCLK_8M 34
#define BAUD_115200_WITH_SMCLK_8M 69
#define BAUD_9600_WITH_SMCLK_8M     873   // also tried with 768 as per one of the TI E2E discussion

/************************************************************************************/

void Uart_HW_init(uint8_t baudrate, uint8_t options)
{

    P3SEL |= BIT3+BIT4;                               // P4.4,5 = USCI_A0 TXD/RXD
    UCA0CTL1 |= UCSWRST;                      // **Put state machine in reset**
    UCA0CTL1 |= UCSSEL__SMCLK;       // SMCLK. 8 MHz clock source

    // //setting baud rate of 460800 with smclk = 8 MHz
    // UCA0BR0 = BAUD_460800_WITH_SMCLK_8M; //
    // UCA0BR1 = 0;
    // UCA0MCTL |= UCBRS_3 + UCBRF_0 + UCOS16; // Modulation UCBRSx=3, UCBRFx=0, oversampling = No

    // //setting baud rate of 230400 with smclk = 8 MHz
    // UCA0BR0 = BAUD_230400_WITH_SMCLK_8M; //
    // UCA0BR1 = 0;
    // UCA0MCTL |= UCBRS_6 + UCBRF_0 ; // Modulation UCBRSx=6, UCBRFx=0, oversampling = No

    //setting baud rate of 115200 with smclk = 8 MHz
    UCA0BR0 = BAUD_115200_WITH_SMCLK_8M; 
    UCA0BR1 = 0;
    UCA0MCTL |= UCBRS_4 + UCBRF_0 ; // Modulation UCBRSx=4, UCBRFx=0, oversampling = No

    // //setting baud rate of 9600 with smclk = 8 MHz
    // UCA0BR0 = BAUD_9600_WITH_SMCLK_8M - ((BAUD_9600_WITH_SMCLK_8M >> 8) << 8);
    // UCA0BR1 = BAUD_9600_WITH_SMCLK_8M >> 8;
    // UCA0MCTL |= UCBRS_7 + UCBRF_0; // Modulation UCBRSx=0, UCBRFx=0, oversampling = No 

    UCA0CTL1 &= ~UCSWRST; // Initialize USCI state machine
    UCA0IE |= (UCRXIE); // Enable USCI_A0 RX interrupt

}

We are not able to communicate with baud rates 115200 or more.,

Can you please help us to find where we are going wrong. 

Thanks and Regards,

Bharat G

Thank You Jens-Michael Gross,

Followings are information of my MSP430 board.

1. MSP430 series -> MSP430F5529.

2. I have attached 32768 Hz crystal to XT1.

3. DCO now increased to 20 MHz. Please find the code for clock setting.

4. XT1 CLK crystal is used as reference for DCO (FLLREFCLK). And as you mentioned even with this setup still I can see 5% error in DCO output.

5. Now this DCO is used as clock source for UART module. This ensures that UART divider value is always greater than 32 and it will keep away from jitter problems due to averaging.

6. I still facing problem in communication.

7. Please look into following code. If everything is correct with the settings then I need to work on the way I handling Packet (Bunch of Bytes after they arrive).

Please do correct me if I am wrong in setting any part of it.

System Clock Setting code :

void System_Init( void )
{

////-------------------CLOCK------------------------------------------------
//// ACLK = 32kHz, MCLK = SMCLK = 20MHz
////
P5SEL |= BIT4 + BIT5;;                 // Select XT1
UCSCTL6 &= ~(XT1DRIVE_0);    // Max drive on XTAL
UCSCTL6 |= XCAP_3;                  // Internal load cap. 6pF, enough?

// Loop until XT1,XT2 & DCO fault flag is cleared
do
{
UCSCTL7 &= ~(XT2OFFG + XT1LFOFFG + DCOFFG);  // bit XT1HFOFFG of register UCSCTL7 is not available in MSP430F5529
                                                                                                 // Clear XT2,XT1,DCO fault flags
SFRIFG1 &= ~OFIFG;                                                           // Clear fault flags
} while (SFRIFG1&OFIFG);                                                   // Test oscillator fault flag
UCSCTL6 &= ~(XT1DRIVE_3);                                            // Xtal is now stable, reduce drive strength

UCSCTL0 = 0x0000;                                                              // Set lowest possible DCOx, MODx
UCSCTL1 = DCORSEL_6;                                                    // Select DCO range 16MHz operation
UCSCTL2 = 610;

UCSCTL4 = SELA__XT1CLK | SELS__DCOCLK | SELM__DCOCLK ;              // use 32k xtal

P2SEL |= BIT2 ;                                                                     //for debug; to scope SMCLK clock and check stability.
__no_operation();

}

UART initialization code :

void Uart_HW_init(uint8_t baudrate, uint8_t options)
{
  P3SEL |= BIT3+BIT4; // P4.4,5 = USCI_A0 TXD/RXD
  UCA0CTL1 |= UCSWRST; // **Put state machine in reset**
  UCA0CTL1 |= UCSSEL__SMCLK; // SMCLK
  UCA0BR0 = 173; // 115200 Baud
  UCA0BR1 = 0;
  UCA0MCTL |= UCBRS_5 + UCBRF_0; // Modulation UCBRSx=5, UCBRFx=0
  UCA0CTL1 &= ~UCSWRST; // Initialize USCI state machine
  UCA0IE |= (UCRXIE); // Enable USCI_A0 RX interrupt
  tx_iptr = 0;
  tx_optr = 0;
}

UART Service routine :

#pragma vector=USCI_A0_VECTOR
__interrupt void USCI_A0_ISR(void)
{
  switch (__even_in_range (UCA0IV, 4))
  {
    // Vector 0 - no interrupt
    case 0 :
    break;

    // Vector 2 - RXIFG
    case 2 :
    if(_RxEventHandle!=NULL)
   {
      _RxEventHandle(UCA0RXBUF);
    }
    LPM3_EXIT;
    break;

    // Vector 4 - TXIFG
    case 4 :
    if (tx_iptr != tx_optr)
    {
      UCA0TXBUF = tx_buf[tx_optr];
      tx_optr++;
      tx_optr &= (SERIAL_TX_MAX_LEN-1);
      if (tx_optr == tx_iptr)
      {
        UCA0IE &= ~UCTXIE; // Disable USCI_A0 TX interrupt
        tx_iptr = 0;
        tx_optr = 0;
      }
  }
  break;

  default :
  break;
}
}

Thank You and Best Regards,

Bharat Gebise

For MCLK >8MHz, you’ll need to raise PMMCOREV. Else the CPU hasn’t enough voltage to run and anything can happen.

Your sample code says its using UARTA0, when we changed to A1, the program is working fine.