main.c

SCI using interrupts on HCS12

/*
Travis Lytle
ECET 309 serial communication with interrupts

This takes the input from SCI0 and flashes an led when any input is recieved.  
When ctrl-x is enter the input is transmitted back out on the SCI0
*/

#include <hidef.h>      /* common defines and macros */
#include <mc9s12db128.h>     /* derivative information */
#pragma LINK_INFO DERIVATIVE "mc9s12db128a"

void initSCI0(void);
void initOC0(void);
void delay(int);

unsigned char textinput[40];
unsigned int cnt;
char x =0;

#pragma CODE_SEG NON_BANKED
void interrupt 20 isr_SCI0(void)	//checks to see if in send or receive mode
{
  if((SCI0SR1 & 0x20) == 0x20){    //check receive flag (RDRF)
      char x;
      x = SCI0SR1;      
      textinput[cnt] = SCI0DRL;  
      cnt++;
      PORTA = 0xFF;
      delay(2);
      PORTA = 0x00;
  }

  if((SCI0SR1 & 0x80) == 0x80){    //check transmit flag (TDRE)
    cnt =0;   
    while(cnt <41) {
    
      if ((SCI0SR1 & 0x40) == 0x40){
        SCI0DRL = textinput[cnt];
        cnt++;
      }
    }
	//clear flags
    SCI0CR2 = 0x24;
    x = SCI0SR1;     //status reg    clears RDRF flag
    x = SCI0DRL;     //data reg
    SCI0CR2 = 0x24;
  
    //reset counter and clear array
    cnt =0;
    for(cnt;cnt<41;cnt++){
      textinput[cnt]=0;
    }
    cnt =0;
  }
}
#pragma CODE_SEG DEFAULT


void main(void) {
  initOC0();
  initSCI0();
  DDRA = 0xFF; 

  x = SCI0SR1;
  SCI0DRL = x;
  
  EnableInterrupts;
  while(1) 
  {
 
  if(cnt != 0)
    if(textinput[(cnt-1)] == 0x18)  // check for ctrl-x if so go into transmit mode
      SCI0CR2 = 0x88;
  }
}

//Serial Comm Interface initalization
void initSCI0() {
  
  SCI0BDH = 0x00;  //Baud Rate H Byte
  SCI0BDL = 26;  //Baud Rate L Byte    9600baud
  SCI0CR1 = 0x00;  
  SCI0CR2 = 0x24;  //  0x24 recieve only   0x88 transmit only
  x = SCI0SR1;     //status reg    clears RDRF flag
  x = SCI0DRL;     //data reg
}

//initialization of the output compare timer
void initOC0() 
{
	TIOS = 1;
	TSCR2 = 4;
	TSCR1 = 0x80;
}
//delay code converted from assembly
void delay(int cnt)					//accepts value for the amount of delay wanted
{
  TCNT = TC0;
  while(cnt > 0) 					//while passed value cnt is greater than zero do the following
  {
    TFLG1 = TFLG1 | 1;  
    TC0 = TC0 + 1500;
      while((TFLG1 & 1)==0){;}		//while TFLG1 logically bit anded with 1 equal 0, wait here
    cnt--;							//decrement counter
  }
}