MSP430FR5989 UART串口初始化的问题

void UCA0_uart_init()

{

P2OUT &= ~(BIT0+BIT1);

P2DIR  &= ~(BIT0+BIT1);

P2REN &= ~(BIT0+BIT1);

P2SEL0 |= BIT0 + BIT1;

P2SEL1 &= ~(BIT0 + BIT1);

UCA0CTLW0 |= UCSWRST | UCSSEL__ACLK;  // Put eUSCI in reset, select ACLK; when ACLK = 32768

UCA0BR0 = 0x03; // 32000/9600 = 3.333     波特率9600

UCA0BR1 = 0x00;

UCA0MCTLW |= 0x4900;

UCA0CTL1 &=~ UCSWRST; // release from reset

UCA0IE |= UCRXIE; // Enable RX interrupt

}

的电压,发现TxD管脚的电压为高电平3.0V,RxD管脚悬空状态(电压一会0V,一会0.8V),请问这样正常吗,串口RxD管脚配置成这样有什么问题吗?

6 个回复

  • 官网有例程的,建议先参考下例程

    //******************************************************************************
    //  MSP430FR69xx Demo - eUSCI_A0 UART echo at 9600 baud using BRCLK = 8MHz
    //
    //  Description: This demo echoes back characters received via a PC serial port.
    //  SMCLK/ DCO is used as a clock source and the device is put in LPM3
    //  The auto-clock enable feature is used by the eUSCI and SMCLK is turned off
    //  when the UART is idle and turned on when a receive edge is detected.
    //  Note that level shifter hardware is needed to shift between RS232 and MSP
    //  voltage levels.
    //
    //  The example code shows proper initialization of registers
    //  and interrupts to receive and transmit data.
    //  To test code in LPM3, disconnect the debugger.
    //
    //  ACLK = VLO, MCLK =  DCO = SMCLK = 8MHz
    //
    //                MSP430FR6989
    //             -----------------
    //       RST -|     P2.0/UCA0TXD|----> PC (echo)
    //            |                 |
    //            |                 |
    //            |     P2.1/UCA0RXD|<---- PC
    //            |                 |
    //
    //   William Goh
    //   Texas Instruments Inc.
    //   April 2014
    //   Built with IAR Embedded Workbench V5.60 & Code Composer Studio V6.0
    //******************************************************************************
    #include <msp430.h>
    
    int main(void)
    {
      WDTCTL = WDTPW | WDTHOLD;                 // Stop Watchdog
    
      // Configure GPIO
      P2SEL0 |= BIT0 | BIT1;                    // USCI_A0 UART operation
      P2SEL1 &= ~(BIT0 | BIT1);
    
      // Disable the GPIO power-on default high-impedance mode to activate
      // previously configured port settings
      PM5CTL0 &= ~LOCKLPM5;
    
      // Startup clock system with max DCO setting ~8MHz
      CSCTL0_H = CSKEY >> 8;                    // Unlock clock registers
      CSCTL1 = DCOFSEL_3 | DCORSEL;             // Set DCO to 8MHz
      CSCTL2 = SELA__VLOCLK | SELS__DCOCLK | SELM__DCOCLK;
      CSCTL3 = DIVA__1 | DIVS__1 | DIVM__1;     // Set all dividers
      CSCTL0_H = 0;                             // Lock CS registers
    
      // Configure USCI_A0 for UART mode
      UCA0CTLW0 = UCSWRST;                      // Put eUSCI in reset
      UCA0CTLW0 |= UCSSEL__SMCLK;               // CLK = SMCLK
      // Baud Rate calculation
      // 8000000/(16*9600) = 52.083
      // Fractional portion = 0.083
      // User's Guide Table 21-4: UCBRSx = 0x04
      // UCBRFx = int ( (52.083-52)*16) = 1
      UCA0BR0 = 52;                             // 8000000/16/9600
      UCA0BR1 = 0x00;
      UCA0MCTLW |= UCOS16 | UCBRF_1 | 0x4900;
      UCA0CTLW0 &= ~UCSWRST;                    // Initialize eUSCI
      UCA0IE |= UCRXIE;                         // Enable USCI_A0 RX interrupt
    
      __bis_SR_register(LPM3_bits | GIE);       // Enter LPM3, interrupts enabled
      __no_operation();                         // For debugger
    }
    
    #if defined(__TI_COMPILER_VERSION__) || defined(__IAR_SYSTEMS_ICC__)
    #pragma vector=USCI_A0_VECTOR
    __interrupt void USCI_A0_ISR(void)
    #elif defined(__GNUC__)
    void __attribute__ ((interrupt(USCI_A0_VECTOR))) USCI_A0_ISR (void)
    #else
    #error Compiler not supported!
    #endif
    {
      switch(__even_in_range(UCA0IV, USCI_UART_UCTXCPTIFG))
      {
        case USCI_NONE: break;
        case USCI_UART_UCRXIFG:
          while(!(UCA0IFG&UCTXIFG));
          UCA0TXBUF = UCA0RXBUF;
          __no_operation();
          break;
        case USCI_UART_UCTXIFG: break;
        case USCI_UART_UCSTTIFG: break;
        case USCI_UART_UCTXCPTIFG: break;
      }
    }
    


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  • 回复 dirtwillfly:

    好的谢谢。那也就是串口的两个管脚默认配置为高阻状态了,还有UART的时钟源选择外部时钟ACLK应该没什么问题吧。
  • 回复 user6052347:

    看你的串口需要的波特率。ACLK一般是低速时钟,不能支持串口工作在较高的波特率。

    如果工作在9600以上,推荐用smclk或者mclk。


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  • 回复 dirtwillfly:

    我刚好选在9600,那推荐用SMCLK或者MCLK吧
  • 回复 user6052347:

    (1) Peripherals are in a state that requires or uses a clock with a "high" frequency of more than 50 kHz.

    (2) Peripherals are in a state that requires or uses a clock with a "low" frequency of 50 kHz or less.

    另外建议看一下 http://www.ti.com/lit/ug/slau367o/slau367o.pdf 的 Table 30-5. Recommended Settings for Typical Crystals and Baud Rates

    If a post answers your question, please mark it with the "verify answer" button.

    若是回复解决了您的问题,请点击“是”确认答案。谢谢!

  • 回复 user6052347:

    9600用32.768k的aclk也可以的,误差会稍微大一点。一般应用问题也不大。

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