PS/2 Keyboard To 16x2 LCD

The Software
           The code is too long to include everything on this page, so I'll just cover the two important specifics:
    -Main Scan Code Look-up
    -Capture Interrupt Routine



           The main program loop is used to decode the scan-code and print the appropriate key. An excerpt of the switch statement that does this can be seen below.

Main Loop

#include <p18f452.h>
#include <cature.h>
#include <timers.h>
#include <delays.h>
..
...
..
void main(void){
TRISA = 0x00;
TRISB = 0x00;
TRISC = 0xFF;
TRISD = 0x01;
PORTA = 0x00;
PORTB = 0x00;
PORTC = 0x00;
PORTD = 0x00;
Delay10KTCYx(10);
INTCON = 0b11000000;
OpenCapture1( C1_EVERY_FALL_EDGE & CAPTURE_INT_ON );
OpenTimer1( TIMER_INT_ON & T1_SOURCE_INT & T1_PS_1_1 & T1_16BIT_RW );
WriteTimer1( 0x0000 );
while(1)
{
     if(buf_ready == 1){
     switch(scan_code_buf[0]){
     case 0x1C : prnt('a');
          break;
     ...
     ....
     ..
          break;
     case 0x45 : prnt('0');
          break;
     case 0x66 : commd(0b00010000);
          break;
     default :
          break;
     }
     //Shift Buffer Forward
     scan_code_buf[0] = scan_code_buf[1];
     scan_code_buf[1] = scan_code_buf[2];
     scan_code_buf[2] = scan_code_buf[3];
     scan_code_buf[3] = scan_code_buf[4];
     scan_code_buf[4] = scan_code_buf[5];
     scan_code_buf[5] = scan_code_buf[6];
     scan_code_buf[6] = scan_code_buf[7];
     scan_code_buf_cnt--;

          if(scan_code_buf_cnt == 0)
               buf_ready = 0;
     }
          Delay10KTCYx(1);
}
}

           Basically, the switch statement pulls from the scan code FIFO and checks if it matches any codes in the switch-statement look up table. If it does some output occurs, whether it is a letter/number print or a delete function. Below is the capture routine for understanding the PS/2 clock and data inputs. The capture function catches PS/2 data until a full PS/2 communication completes, then it throws the data into a FIFO buffer for the main loop to evaluate.

Two Interrupt Service Routines

void InterruptHandlerHigh(void) // Declaration of InterruptHandler
          //Check If TMR1 Interrupt Flag Is Set
     if(PIR1bits.CCP1IF){
          if(bit_counter < 10){
               current_scan_code = current_scan_code >> 1;
               current_scan_code += (PORTDbits.RD0*0b10000000000);
               bit_counter++;
          }
          else if(bit_counter == 10){
scan_code_buf[scan_code_buf_cnt]=(current_scan_code>>2)&0xFF;
               scan_code_buf_cnt++;
               buf_ready = 1;
               bit_counter = 0;
          }
          WriteTimer1( 0x0000 );
          //Clear CCP1 Overflow Flag Bit
          PIR1bits.CCP1IF = 0;
     }
          //Check If CCP1 Interrupt Flag Is Set
     else if(PIR1bits.TMR1IF){
          //Clear Timer1 Overflow Flag Bit
          bit_counter = 0;
          PIR1bits.TMR1IF = 0;
     }
     INTCONbits.GIE = 1;
}

           As you can see above, the Capture module interrupt and timer1 are used together to make sure that we only catch the 8 data bits and not the start, stop or parity bits. I'm sure a better parsing routine could be created, but for now, the one above works just fine.