MSP430F149 serial RS485 interface

    The basic principles and usage of RS485 communication are the same as RS232, with the following differences.

RS232 interface can only realize point-to-point communication, but this method cannot realize networking function, so RS485 appeared to solve this problem. RS485 uses differential signal negative logic, +2V~+6V represents "1", -6V~-2V represents "0". For dual-machine communication, only AA and BB connections are needed.

The hardware circuit generally uses RS485 level conversion chips such as SN65176. When connected to the MCU, there are three pins: DE (RE and DE are connected together), DI (receive pin), RO (send pin). When the MCU sends a frame signal, it must first enable DE=1; before receiving the signal, it must first enable DE=0 (ie RE=0).

2. Examples

2.1 Send character 8.N.1.2400

#define DRE_out P3DIR |= BIT3 //Connect the DE and RE ports of the 485 chip to the output state

#define DE P3OUT |= BIT3 //Set the 485 chip to the sending state

void Set_UART1(void)

{

    P3SEL |= 0xC0; //Select P3.6 and P3.7 as the communication port of UART1

    ME2 |= UTXE1 + URXE1; // Enable TXD and RXD of USART1

    UCTL1 |= CHAR; //Select 8-bit character

    UTCTL1 |= SSEL0; //Drive clock selection ACLK

    UBR01 = 0x0D; //Baud rate 2400

    UBR11 = 0x00;

    UMCTL1 = 0x6B; //Adjust

    UCTL1 &= ~SWRST; //Initialize UART state machine

}

main

{

    DRE_out;

    DE;

    Set_UART1();

    TXDATA = 0X30;

    TXBUF1 = TXDATA; //Here you can directly assign a value to transmit fixed data

while(!(IFG2 & UTXIFG1)); //Wait for sending to end

…

 }

2.2 Interrupt function receives character 8.N.1.2400

void Set_UART1(void)

{

    P3SEL |= 0xC0; //Select P3.6 and P3.7 as the communication port of UART1

    ME2 |= UTXE1 + URXE1; // Enable TXD and RXD of USART1

    UCTL1 |= CHAR; //Select 8-bit character

    UTCTL1 |= SSEL0; //Drive clock selection ACLK

    UBR01 = 0x0D; //Baud rate 2400

    UBR11 = 0x00;

    UMCTL1 = 0x6B; //Adjust

    UCTL1 &= ~SWRST; //Initialize UART state machine

    IE2 |= URXIE1; //Enable UART1 receive interrupt

}

#pragma vector=UART1RX_VECTOR

__interrupt void UART1_RX (void)

{

    Disp1Char(pX++,pY,RXBUF1);

    if(pX == 16)

    {

      pX = 0;

      pY^= 1;

    }

}