#include <avr/io.h>
#include <avr/delay.h>
#define PIN_RXD   0  //PD0   RXD
#define PIN_TXD   1  //PD1   TXD
#define BAUDRATE        9600 //baudrate
//#define F_CPU   8000000 //the frequency of the global clock

unsigned int advalue;
void init_USART(void);
void put_s(unsigned char *ptr);
void put_c(unsigned char c);
int main(void)
{
     //上電默認DDRx=0x00,PORTx=0x00 輸入，無(wú)上拉電阻    
 PORTA=0XFF;                                             //上拉
    PORTB =0xFF;                                            //不用的管腳使能內部上拉電阻。
    PORTC=0XFF;                     
    DDRD  =(1<<PIN_TXD);        //TXD為輸出
    PORTD =0xFF;
 init_USART();
 while(1)
 {
     unsigned char highvalue,lowvalue;
   ADMUX=(1<<REFS0);    //AVCC基準電壓,通道0,10bits ad value
  /*----------------------------------------------------------------
  ADMUX
  7,6       REFS1:0--------Rrference Selection Bits
            00-------------AREF,Internal Vref truned off
      01-------------AVCC with external capacior at AREF pin
      10-------------Reserved
      11-------------internal 2.56V Voltage Reference with external
                     capacitior at AREF pin
  5         ADELAR---------ADC Left Adjust Result
            1--------------Left Adjust-----8 bits resolution
      0--------------Right Adjust----10 bits resolution
  4:0       MUX4:0---------Analog Channel and Gain Selection Bits
            00000----------ADC0
      00001----------ADC1
      ||||||||||||||||||||||||||||||||||||
      00111----------ADC7
      |||||||||||||||||||||||||||||||||||||
  ----------------------------------------------------------------*/
   ADCSRA=(1<<ADEN)|(1<<ADSC)|(1<<ADPS2)|(1<<ADPS1)|(1<<ADPS0);     //AD使能，單次轉換，128分頻
     /*--------------------------------------------------------------------
  ADCSRA
  7         ADEN-----------ADC Enable
  6         ADSC-----------ADC Start Comversion
  5         ADATE----------ADC Auto Trigger Enable
  4         ADIF-----------ADC Interrupt Flag
  3         ADIE-----------ADC Interrupt Enable
  2:0       ADPS2:0--------ADC Prescaler Select Bits
            000------------2
      001------------2
      010------------4
      011------------8
      100------------16
      101------------32
      110------------64
      111------------128
  ---------------------------------------------------------------------*/
     while(!(ADCSRA & (1 << ADIF))); /*等待*/
  advalue=ADC;
  ADCSRA&=(~(1<<ADEN))|(~(1<<ADSC));
  advalue=advalue*4.89;
  highvalue=(unsigned char)(advalue/100);
  lowvalue=(unsigned char)(advalue%100);
  put_s("AD轉換電壓值為:");
  put_c(highvalue/10+0x30);
  put_c('.');
  put_c(highvalue%10+0x30);
  put_c(lowvalue/10+0x30);
  put_c(lowvalue%10+0x30);
  put_s("V\n");
  unsigned char i;
  for(i=0;i<255;i++)
  _delay_ms(20);
 }
}
/*---------------------------------------------------------------------------
function      send an unsigned char to the uart
----------------------------------------------------------------------------*/
void put_c(unsigned char c) //發(fā)送采用查詢(xún)方式
{
 while( !(UCSRA & (1<<UDRE)) );        //wait until the uart is empty
 UDR=c;                                  //write data to uart
}
/*----------------------------------------------------------------------------
function      send  a string to the uart and with return back
-----------------------------------------------------------------------------*/
void put_s(unsigned char *ptr)
{
 while (*ptr)
 {
  put_c(*ptr++);
 }
 put_c(0x0D);
 put_c(0x0A);  //結尾發(fā)送回車(chē)換行
}
/*---------------------------------------------------------------------------
fuction     initialize the uart  unit
----------------------------------------------------------------------------*/
void init_USART(void)//USART 初始化
{

    //USART 9600 8, n,1  PC上位機軟件(超級終端等)也要設成同樣的設置才能通訊
    UCSRC = (1<<URSEL) | 0x06;
    //異步，8位數據，無(wú)奇偶校驗，一個(gè)停止位，無(wú)倍速
    /*
    UBRRH與UCSRC共用I/O 地址。因此訪(fǎng)問(wèn)該地址時(shí)需注意以下問(wèn)題。
    寫(xiě)訪(fǎng)問(wèn)
    當在該地址執行寫(xiě)訪(fǎng)問(wèn)時(shí)， USART 寄存器選擇位(URSEL)控制被寫(xiě)入的寄存器。
    若URSEL為0，對UBRRH值更新；若URSEL為1，對UCSRC設置更新
   
    讀訪(fǎng)問(wèn)
    對UBRRH 或UCSRC 寄存器的讀訪(fǎng)問(wèn)則較為復雜。但在大多數應用中，基本不需要讀這些寄存器
   
   
    沒(méi)有UBRR這個(gè)16位寄存器，因為UBRRL(0x09)/UBRRH(0x20)的地址不連續,而且UBRRH跟UCSRC共用地址
    */
   
    //U2X=0時(shí)的公式計算
    UBRRL= (F_CPU/BAUDRATE/16-1)%256;
    UBRRH= (F_CPU/BAUDRATE/16-1)/256;
    //U2X=1時(shí)的公式計算
    //UBRRL= (F_CPU/BAUDRATE/8-1)%256;
    //UBRRH= (F_CPU/BAUDRATE/8-1)/256;
    //也可根據數據手冊的[波特率設置的例子]查得
    //UBRRL = 0x2F; //set baud rate lo
    //UBRRH = 0x00; //set baud rate hi
    UCSRA = 0x00;                     //無(wú)倍速
    UCSRB = (1<<RXEN)|(1<<TXEN);
    //使能接收，使能發(fā)送
}