demo_14_1.c

AVR原理与应用例程

/*****************************************************
File name           : demo_14_1.c
Chip type           : ATmega16L
Program type        : Application
Clock frequency     : 4.000000 MHz
Memory model        : Small
External SRAM size  : 0
Data Stack size     : 256
*****************************************************/
#include <mega16.h>

#define UART_BEGIN_STX  0xBB
#define UART_END_STX    0xEE

#define RXB8 1
#define TXB8 0
#define UPE 2
#define OVR 3
#define FE 4
#define UDRE 5
#define RXC 7

#define FRAMING_ERROR (1<<FE)
#define PARITY_ERROR (1<<UPE)
#define DATA_OVERRUN (1<<OVR)
#define DATA_REGISTER_EMPTY (1<<UDRE)
#define RX_COMPLETE (1<<RXC)

#define TX_BUFFER_SIZE 5
unsigned char tx_buffer[TX_BUFFER_SIZE];         // USART Transmitter buffer
unsigned char tx_wr_index,tx_rd_index,tx_counter;

// USART Transmitter interrupt service routine
interrupt [USART_TXC] 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;
    }
}

void putchar(unsigned char c)
{
    while (tx_counter == TX_BUFFER_SIZE);
    #asm("cli")
    if (tx_counter || ((UCSRA & DATA_REGISTER_EMPTY)==0))
    {
        tx_buffer[tx_wr_index]=c;
        if (++tx_wr_index == TX_BUFFER_SIZE) tx_wr_index=0;
        ++tx_counter;
    }
    else
        UDR=c;
    #asm("sei")
}

#define RX_BUFFER_SIZE 5
unsigned char rx_buffer[RX_BUFFER_SIZE];     // USART Receiver buffer
unsigned char rx_counter;
bit Uart_RecvFlag;

// USART Receiver interrupt service routine
interrupt [USART_RXC] void usart_rx_isr(void)
{
    unsigned char status,data;
    status = UCSRA;
    data = UDR;
    if (!Uart_RecvFlag)     // 判断是否允许接收一个新的数据包
    {
        if ((status & (FRAMING_ERROR | PARITY_ERROR | DATA_OVERRUN))==0)
        {
            rx_buffer[rx_counter] = data;
            rx_counter++;
            switch (rx_counter)
            {
                case 1:     // 检验起始字符
                    if (data != UART_BEGIN_STX) rx_counter = 0;
                    break;
                case 4:     // 检验校验字
                    if (data != (rx_buffer[1]^rx_buffer[2])) rx_counter = 0;
                    break;
                case 5:     // 检验结束字符
                    rx_counter = 0;
                    if (data == UART_END_STX) Uart_RecvFlag = 1;
                    break;   // Uart_RecvFlag=1，表示正确接收到一个数据包
            }
        }
    }                 
}

void main(void)
{
    unsigned char channel = 0x07;
    unsigned char tx_1,tx_3;
        
    PORTA = ~(0x01<<channel);
    DDRA=0xFF;
    // USART initialization
    UCSRA=0x00;     // Communication Parameters: 8 Data, 1 Stop, No Parity
    UCSRB=0xD8;     // USART Receiver: On, USART Transmitter: On
    UCSRC=0x86;     // USART Mode: Asynchronous, USART Baud Rate: 9600
    UBRRH=0x00;
    UBRRL=0x19;
    #asm("sei")      // Global enable interrupts

    while (1)
    {
        if (Uart_RecvFlag)
        {                       // 有刚接收到数据包需要处理
            tx_1 = 0x00;
            switch (rx_buffer[1])   // 数据包处理过程
            {
                case 0xA0:
                    break;
                case 0xA1:
                    if (rx_buffer[2]>=0x00 && rx_buffer[2]<=0x07)
                    {
                        channel = rx_buffer[2];
                        PORTA = ~(0x01<<channel);
                    }    
                    else
                        tx_1 = 0x02;        
                    break;
                default:
                    tx_1 = 0x01;
                    break;
            }
            tx_3 = tx_1^channel;
            putchar(UART_BEGIN_STX);    // 发送回送数据包
            putchar(tx_1);
            putchar(channel);
            putchar(tx_3);
            putchar(UART_END_STX);
            Uart_RecvFlag = 0;          // 允许接收下一个数据包               
        }
    }
}