*   File: Serial_Comm_1.C
*   Description: Serial Communication Example 1
*   Created Date:  2007-10-01
*   Last Modified: 2007-10-01
*   Author: Jeffrey - Schicksal@126.com
*   Notes: None
**********************************************/
#include "Atmel/AT89X51.h"

unsigned char Read_Keyboard();
void RS232_SendData(unsigned char Sdata);

/**********************************************
*   Function: delay(unsigned int t)
*   Input Variables: t
*   Return Variables: None
*   Usage: Common Delay Routine, t as the delay time ticks
**********************************************/
void delay(unsigned int t)
{
  for(;t>0;t--);  // 延时循环
}

/**********************************************
*   Function: RS232_Init(void)
*   Input Variables: none
*   Return Variables: None
*   Usage: Init UART
**********************************************/
void RS232_Init()
{
 SCON =  0x50;  // UART工作于模式1， REN=1 
 TMOD =  0x20 ;  // Timer1 工业于模式2
 PCON |= 0x80;  // SMOD1 = 1 
 TH1 = 0xF3;   // 波特率9600 Bds at 24MHz 
 TL1 = 0xF3;   // 波特率9600 Bds at 24MHz 
 TR1 = 1;    // 启动Timer1 
}

/**********************************************
*   Function: main()
*   Input Variables: None
*   Return Variables: None
*   Usage: Program Entry
*********************************************/
void main()
{
  unsigned char Keyboard_Status = 0xff;  // 定义键值
  RS232_Init();
  while(1)
  {
    Keyboard_Status = Read_Keyboard(); // 读取按键值
    //********************主程序部分*********************//
    switch(Keyboard_Status)
    {
     case (~0x01):
     {
      RS232_SendData('A');
      break;     
     }
     case (~0x02):
     {
      RS232_SendData('B');
      break;     
     }
     case (~0x04):
     {
      RS232_SendData('C');
      break;     
     }
     case (~0x08):
     {
      RS232_SendData('D');
      break;     
     }
     case (~0x10):
     {
      RS232_SendData('E');
      break;     
     }
     case (~0x20): 
     {
      RS232_SendData('F');
      break;     
     }
     case (~0x40): 
     {
      RS232_SendData('G');
      break;
     }
     case (~0x80): 
     {
      RS232_SendData('H');
      break;
     }
     default:
     //RS232_SendData('X');
     break;
    }
    //********************主程序部分*********************//
  }
}

/**********************************************
*   Function: RS232_SendData(unsigned char Sdata)
*   Input Variables: unsigned char Sdata
*   Return Variables: none
*   Usage: Send a Char to UART
*********************************************/
void RS232_SendData(unsigned char Sdata)
{
 SBUF = Sdata;  // 发送数据
 while(TI==0);  // 等待发送完毕
 TI = 0;       // 清除发送结束标志
}

/**********************************************
*   Function: Read_Keyboard
*   Input Variables: None
*   Return Variables: Keys Value
*   Usage: Read Keyboard Status
*********************************************/
unsigned char Read_Keyboard()
{
  unsigned char Keys_Value=0;    // 定义键值变量
  unsigned char Keys_Temp;
  P2=0xff;
  Keys_Value=P2;
  
    do
  {
   P2 = 0xff;       // P2口置高，准备读取按键状态
   Keys_Temp = P2;      // 读取按键状态
   delay(150);       // 消抖延时
   P2 = 0xff;       // P2口置高，准备读取按键状态
   Keys_Value = P2;     // 读取按键状态
  }
  while(Keys_Value != Keys_Temp);   // 如果读取状态不一致，则重复读取键值
  while(P2!=0xff);      // 直到按键释放
  return Keys_Value;      // 返回按键状态值
}