#include <c8051f020.h>    
#include <stdio.h>
#include <string.h>

#define INBUF_LEN 	4   		//數據長度
#define STARTBYTE	0x24		//
#define MYADD		0xE3		//address
#define SYSCLK		22118400
#define BAUDRATE	2400

unsigned char inbuf1[INBUF_LEN];
unsigned char checksum,count3;
bit     read_flag=0;
sbit	RS485_DE = P0^5;

void Port_Init (void)
{
//ENABLE CROSSBAR, DISABLE WEAK PULL-UP
//UART0, UART1, CEX0~4, TIMER0,TIMER1
//
//P0.0	TX0
//P0.1	RX0
//P0.2	TX1
//P0.3	RX1
//P0.4	CEX0
//P0.5	CEX1
//P0.6	CEX2
//P0.7	CEX3
//P1.0	CEX4
//P1.1	T0
//P1.2	/INT0
//P1.3	T1
//P1.4	/INT1
//P1.5	T2
//P1.6	T2EX
//P1.7
    XBR0      = 0x04;
    XBR2      = 0xC0;

}


void SYSCLK_Init(bit ExtOsc)
{
	int i;    							// delay counter  	

	//initial system clock
   if(ExtOsc)
   {
   		OSCXCN = 0x67;                      // start external oscillator with 22.1184MHz crystal
   		for (i=0; i < 3000; i++) ;           // Wait for osc. to start up
   		while (!(OSCXCN & 0x80)) ;          // Wait for crystal osc. to settle
   		OSCICN = 0x88;                      // select external oscillator as SYSCLK source and enable missing clock detector
   }
   else
   		OSCICN    = 0x07;					// Internal oscilattor 16MHz

}

void init_serialcomm(void)
{
    SCON0  = 0x50;                      // SCON1: mode 1, 8-bit UART, enable RX
    TMOD   = 0x20;                      // TMOD: timer 1, mode 2, 8-bit reload
    TH1    = -(SYSCLK/BAUDRATE/16);     // set Timer1 reload value for baudrate
    TR1    = 1;                         // start Timer1
    CKCON |= 0x10;                      // Timer1 uses SYSCLK as time base
    PCON  |= 0x80;                      // SMOD0 = 1
    ES0 = 1;
}

//向串口發送一個字符 
void send_char_com(unsigned char ch)  
{
	RS485_DE = 1;
    SBUF0=ch;
    while(TI0==0);
    TI0=0;		 
	RS485_DE = 0;
}

//向串口發送一個字符串，strlen為該字符串長度 
void send_string_com(unsigned char *str,unsigned int strlen)
{
    unsigned int k=0;
    do 
    {
        send_char_com(*(str + k));
        k++;
    } while(k < strlen);
}


//串口接收中斷函數 
void serial () interrupt 4 using 1
{
unsigned char ch;

	ES0 = 0;

	if(RI0 && read_flag==0)
    {
		RI0 = 0;
	 	ch = SBUF0;
		if( count3 ==0)	   		//startbyte
		{
			if(ch == STARTBYTE)
				inbuf1[count3++] = ch;
		}
		else 
			if(count3 == 1)		//add
			{
			 	if(ch == MYADD)
					inbuf1[count3++] = ch;
				else
					count3 = 0;
			}
			else
			{
				inbuf1[count3++] = ch;
				
				if(count3 == 4)
				{
			 		count3 =0;
					read_flag = 1;
				}
			}
	 }
	 ES0 = 1;

}


main()
{
    WDTCN = 0xde;				// 禁止看門狗
	WDTCN = 0xad;

 	Port_Init();
	SYSCLK_Init(1);

    init_serialcomm();  //初始化串口 
	RS485_DE = 0;
	EA = 1;
	
    while(1)
    {
          if(read_flag)  //如果取數標志已置位，就將讀到的數從串口發出 
          {
               read_flag=0; //取數標志清0 
               send_string_com(inbuf1,INBUF_LEN);
          }
    }
}