/*****************************************************
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?

#define?UART_BEGIN_STX??0xBB
#define?UART_END_STX????0xEE

#define?FRAMING_ERROR?（1<#define?PARITY_ERROR?（1<#define?DATA_OVERRUN?（1<#define?DATA_REGISTER_EMPTY?（1<#define?RX_COMPLETE?（1<
#define?TX_BUFFER_SIZE?5
unsigned?char?tx_buffer[TX_BUFFER_SIZE];?????????//?USART?Transmitter?buffer
unsigned?char?tx_wr_indextx_rd_indextx_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?statusdata;
????status?=?UCSRA;
????data?=?UDR;
????if?（!Uart_RecvFlag）?????//?判斷是否允許接收一個新的數據包
????{
????????if?（（status?&?（FRAMING_ERROR?|?PARITY_ERROR?|?DATA_OVERRUN））==0）
????????{
????????????rx_buffer[rx_counter]?=?data;
????????????rx_counter++;
????????????switch?（rx_counter）
????????????{
????????????????case?1:?????//?檢驗起始字符
???????