key.c

该设备是一款基于AVR mega16L单片机的电子书阅读器

/****************************************************************************** 
 * PC/AT keyboard driver. 
 * Based in part on Atmel's application note AVR313. www.atmel.com
******************************************************************************/
#include <mega16.h>
#include <key.h>
#include <scancodes.h> 
#include <delay.h>  

/******************************************************************************
 * InitializeKeyboard()
 * Initializes the ports and control registers needed for running the keyboard.
******************************************************************************/
unsigned char edge;        /* 0 = neg.  1 = pos. */
unsigned char bitcount;
void InitializeKeyboard( void )
{   
   GICR =0x40;     /* enable INT0 interrupt */
   #asm("sei");                /* enable global intterupts */
   MCUCR =0x02;    /* trigger INT0 on falling edge */
   DDRD&=~0x0c; 
   PORTD|=0x0c;
    /* PD2, PD3 are inputs */	
   edge = 0;
   bitcount = 11;
   return;
}
/******************************************************************************
 * interrupt [EXT_INT0] void ext_int0_isr (void)
 * When the keyboard triggers the external interrupt this function is called
 * to retrieve the data.
******************************************************************************/
interrupt [EXT_INT0] void ext_int0_isr (void)
{
   static unsigned char    scancode = 0;
    if(!edge)                               // Routine entered at falling edge
    {
        if( ( bitcount < 11 ) && ( bitcount > 2 ) )    
        {
           // Bit 3 to 10 is data. Parity bit, start and stop bits are ignored.
            scancode = ( scancode >> 1 );
            if( PIND&0x08 )            //如果数据是1 PD3是键盘数据输入端，PO2是中断口
            {
                scancode = scancode | 0x80;  // Store a '1' for this bit
            }
        }
          MCUCR=0x03;                 // Set interrupt on rising edge
          edge = 1;        
    } 
    else                                     // Routine entered at rising edge
    {                                
        MCUCR =0x02;                 // Set interrupt on falling edge
        edge = 0;
        if(--bitcount == 0)                  // All bits received
        {
           bitcount = 11;
           key= Decode( scancode );
        }
    }
}
unsigned char Decode( unsigned char scancode )
{      
       int i = 0; 
       unsigned char temp = 0;
       static unsigned char   shift = 0;
       unsigned char key_value=0;
      if( ( scancode == 0x12 ) || ( scancode == 0x59 ) ) 
           {
              // left or right shift按住SHIFT键
              shift = 1;              
           }
           else                                             
           {
              // a key other than shift was pressed, do a table look-up      
              for( i = 0; i < 50; i++ )//查表，寻找对应键值
              {
	       temp = char_table[i*3];//PRG_RGB可能因为要用FLASH中数据要用此函数
          	                                                 //i*3应该是表中各键值对应初始地址，因为一块就要三个数据
               if ( temp == scancode ) 
                 {
                    if( shift )                              //如果按了SHIFT就取后面那个大些的字母
                    {
                       key_value = char_table[i*3+2];
                    }
                    else
                    {
		       key_value = char_table[i*3+1];
                    }
		    break;
                 }
              }		       
              shift = 0;             
           } 
         delay_ms(20);
         return  key_value;               
}