//Interrupt Programming with CodeWarrior for HCS12G128 Tower module Using SCI0 Interrupt.
//Toggling PTT7 continuously while waiting for Interrupt to come in from SCI0
//Pressing any key on x86 PC HyperTerminal/Tera Terminal and it will cause interrupt 
//and HCS12G128 gets the character and displays it on LEDs of PORTT
//Modified and tested by Mazidi from Example 11-12C of Chapter 11 of HCS12 textbook by Mazidi & Causey

//On TWR-S12G128 Serial COM0 (SCI0) is IDC 2x5 male header located next to brown POT. 
//The TWR-S12G128 board comes with a DB9-to-IDC-2x5 femal cable for connecting it to the COM port of x86 PC
//When connecting female IDC 2x5 to Tower,make sure pin 1 on IDC Tower board is lined up with the red stripe of the IDC-2x5 cable 
//If the IDC-2x5 cable is connected right, then RED stripe will be on side of USB power cable

//If your x86 PC does not have Serial COM port (with DB-9 connector)then you need USB to Serial Converter
//The best one we have seen is (TRENDnet USB to RS-232 Serial Converter TU-S9) from Amazon
//http://www.amazon.com/TRENDnet-RS-232-Serial-Converter-TU-S9/dp/B0007T27H8/ref=pd_bxgy_e_img_y


//Make sure to choose "minimal startup code" and "Small" for memory model(no banked) when creating porject for Interrupts 

//In Codewarrior, make sure you are in Open Source BDM
//In Codewarrior F7(make), F5(Debug) and F5 again to start running

//Bring up Hyper Terminal in Windows XP (or Tera Terminal in Windows Vista and Windows 7)
//Click on Hyper/Tera Terminal after the message "YES" is displayed
//Now,as you press a key, the ASCII char in binary appears on PT6-PT0 


//Close and re-open HyperTerminal/TeraTerminal everytime you run this program 



#include <hidef.h>      /* common defines and macros */
#include "derivative.h"      /* derivative-specific definitions */
void SerTx0(unsigned char);
void MSDelay(unsigned int);
void main(void) 
{
  DDRT = 0xFF;      	//PortT as output
  PER0AD = 0x80;	// enable PU on PAD15 to enable COM for the HCS12G128 chip
                         //Notice this is different from HCS12DP256/512
    SCI0BDH=0x00;     
    SCI0BDL=41;     //12.5 MHz/2=6.25MHz, 6.25MHz/16=390,625 Hz and 390,625/9600=41 
    SCI0CR1=0x00;
    SCI0CR2=0x2C;    //enable receive interrupt too
  
    __asm CLI;  //Enable interrupts globally
   //EnableInterrupts;  	//another way to Enable interrupts globally

//Test serial SCI0 by sending "YES" to Hyper/Tera Terminal to make sure it works.

      	SerTx0('Y');
        SerTx0('E');
        SerTx0('S');
        SerTx0(' ');
//Test the PTT by sending 0xAA and 0x55 to make sure they work.
	      PTT = 0x55;
        MSDelay(1000);    
        PTT = 0xAA;
        MSDelay(1000);  			
  
  for(;;) 
  {                      //Now, do something until interrupt comes in
  
  PTT = PTT ^ 0x80;      //Toggle PT7 (LED4) forever and wait for interrupt

  MSDelay(100);
  
  } //stay here until interrupt comes.
}

   
//SCI0 Interrupt, Pressing any key on HyperTerminal/TeraTerminal will send a charater to HCS12G128 Tower Module via SCI0 port
//and HCS12G128 gets the character and displays it on PORTT. 
//Notice the PT6-PT4 (LED3-LED1) LEDs show only the upper 3 bits of the ASCII character coming in from Terminal while LED4 keeps toggling
//Make sure you click on Hyper /Tera Terminal and press numbers, small letters, capital letters and see the LED3-1
//To get the lower 4 bits of the ASCII char you need to connect 4 LEDs to PT3-PT0 pins on a breadboard
//Make sure this 4 LEDs are active LOW..    

interrupt (((0x10000-Vsci0)/2)-1) void SCI0_ISR(void)
//interrupt VectorNumber_Vsci0 void SCI0_ISR(void)  //another way to declare interrupt
  {
   if(SCI0SR1 & SCI0SR1_RDRF_MASK)	
     PTT=~SCI0DRL;	//since LEDs connected to PortT are active LOW
    
  }   
  
 void MSDelay(unsigned int itime)
  {
    unsigned int i; unsigned int j;
    for(i=0;i<itime;i++)
      for(j=0;j<1000;j++);
  }


void SerTx0(unsigned char c)  //SCI0 (COM0 of HCS12 chip)
  {
    while((SCI0SR1 & 0x80)==0);  //make sure the last bit is gone
    SCI0DRL=c;		       //before giving it another byte	
  }