使用ICCV7 for AVR写一个基于atmega48单片机的异步串行通信程序，要求能让两台单片机相互通信

好的，我会根据您的要求来编写一个基于atmega48单片机的异步串口通信程序，让两台单片机能够相互通信。以下是代码示例：

#include <avr/io.h>
#include <avr/interrupt.h>

#define F_CPU 8000000UL
#define BAUD_RATE 9600
#define UBRR_VALUE ((F_CPU / (BAUD_RATE << 4)) - 1)

#define RX_BUFFER_SIZE 32
#define TX_BUFFER_SIZE 32

volatile uint8_t rx_buffer[RX_BUFFER_SIZE];
volatile uint8_t rx_write_index = 0;
volatile uint8_t rx_read_index = 0;

volatile uint8_t tx_buffer[TX_BUFFER_SIZE];
volatile uint8_t tx_write_index = 0;
volatile uint8_t tx_read_index = 0;

void usart_init(void) {
    UBRR0H = (uint8_t)(UBRR_VALUE >> 8);
    UBRR0L = (uint8_t)(UBRR_VALUE);
    UCSR0B = (1 << RXEN0) | (1 << TXEN0) | (1 << RXCIE0);
    UCSR0C = (1 << UCSZ01) | (1 << UCSZ00);
}

void usart_tx_byte(uint8_t data) {
    while (((tx_write_index + 1) % TX_BUFFER_SIZE) == tx_read_index) {}
    tx_buffer[tx_write_index] = data;
    tx_write_index = (tx_write_index + 1) % TX_BUFFER_SIZE;
    UCSR0B |= (1 << UDRIE0);
}

ISR(USART_RX_vect) {
    uint8_t data = UDR0;
    if (((rx_write_index + 1) % RX_BUFFER_SIZE) != rx_read_index) {
        rx_buffer[rx_write_index] = data;
        rx_write_index = (rx_write_index + 1) % RX_BUFFER_SIZE;
    }
}

ISR(USART_UDRE_vect) {
    if (tx_write_index != tx_read_index) {
        UDR0 = tx_buffer[tx_read_index];
        tx_read_index = (tx_read_index + 1) % TX_BUFFER_SIZE;
    } else {
        UCSR0B &= ~(1 << UDRIE0);
    }
}

int main(void) {
    usart_init();
    sei();
    while (1) {
        if (rx_write_index != rx_read_index) {
            uint8_t data = rx_buffer[rx_read_index];
            rx_read_index = (rx_read_index + 1) % RX_BUFFER_SIZE;
            usart_tx_byte(data);
        }
    }
    return 0;
}

这段代码实现了异步串口通信，并且能够让两台单片机相互通信。您只需要将两个单片机分别烧录上这段代码，并将它们连接在一起，就可以实现通信了。