usart.c

AVR的SPI的通信例子

#include "USART.h"
#include "main.h"

volatile INT8U rx_enable=0;
volatile INT8U  rx_buffer[RX_BUFFER_SIZE];  // USART0 Receiver buffer
volatile INT8U rx_wr_index=0;
volatile INT8U  rx_rd_index=0;
volatile INT8U  rx_counter=0;
volatile INT8U  rx_buffer_overflow=0; // This flag is set on USART Receiver buffer overflow



volatile char tx_buffer[TX_BUFFER_SIZE];    // USART0 Transmitter buffer
volatile unsigned char tx_wr_index=0;
volatile unsigned char tx_rd_index=0;
volatile unsigned char tx_counter=0;


void  USART_Init(void)
{
 UCSRB = 0x00; //disable while setting baud rate
 UCSRA|= 1<<U2X;
 UCSRC = 0x86;
 UBRRL = BAUDL;
 UBRRH = BAUDH;
 UCSRB = 0xD8;
}


// USART0 Receiver interrupt service routine
#pragma vector=USART_RXC_vect
__interrupt  void usart_rx_isr(void)
{
    INT8U  status,data;

    status=UCSRA;
    data=UDR;
    if ((status & (FRAMING_ERROR | PARITY_ERROR | DATA_OVERRUN))==0)
    {
        rx_enable=1;
        rx_buffer[rx_wr_index]=data;
        if (++rx_wr_index == RX_BUFFER_SIZE) rx_wr_index=0;
        if (++rx_counter == RX_BUFFER_SIZE)
            {
              rx_counter=0;
              rx_buffer_overflow=1;
            }
    }
}


// Get a character from the USART Receiver buffer
INT8U GetChar(void)
{
    INT8U  data;
    while(rx_counter==0);
    data=rx_buffer[rx_rd_index];
    if (++rx_rd_index== RX_BUFFER_SIZE) rx_rd_index=0;
    __disable_interrupt();
    --rx_counter;
    __enable_interrupt();
    return data;
}


// USART0 Transmitter interrupt service routine
#pragma vector=USART_TXC_vect
__interrupt  void usart_tx_isr(void)
{
  if (tx_counter)
    {
      --tx_counter;
      UDR=tx_buffer[tx_rd_index];
      if (++tx_rd_index == TX_BUFFER_SIZE) tx_rd_index=0;
    };
}


// Write a character to the USART0 Transmitter buffer
void PutChar(INT8U data)
{

    while (tx_counter == TX_BUFFER_SIZE);
    __disable_interrupt();
    if (tx_counter || ((UCSRA & DATA_REGISTER_EMPTY)==0))
      {
        tx_buffer[tx_wr_index]=data;
        if (++tx_wr_index == TX_BUFFER_SIZE) tx_wr_index=0;
        ++tx_counter;
      }
    else
        UDR=data;
   __enable_interrupt();
}