// Test1: Using Tiny 13 to detect field clock and to control the MOD input in the transponder to send one data byte
// protocol: byte(00000000) byte(11111111) byte(11111111) 100 byte(data).  
//optimized to send 3 synch bites and then 100 bytes
// with tempreature sensor
/* This code is for the AtmelTiny13 Microcontroller */

/************************************
//Port Description   

Connect XT1 on PORTE to PB3(XTAL1 on 2323) on PORTB

Inputs:
B.2 = Field Clock Input (T0)
B.4 = ADC input ADC2

Outputs:
B.0 = Manchester data output
B.1 = 2 KHz Clock

*/

#include <Tiny13.h>

void initialize(void);   //all the ini stuff          
unsigned char voltageD, index, byte, halfcycle;  //digital voltage, index for data,number of half-cycles field clock has gone //through transmission, byte  

//**********************************************************
//timer 0 compare ISR
interrupt [TIM0_COMPA] void timer0_com(void)
{
   	// Three sync bytes (00-ff-ff), then 100 data bytes.
  	
	PORTB.1 = ~PORTB.1;
	   
    // Byte boundary.
    if (halfcycle == 16)
    {   

   	halfcycle = 0;
        voltageD=ADCH;
	if (voltageD == 255) voltageD = 0;
    	
	ADCSRA.6=1;
        
    	if (index == 0)     byte = 0x00;
    	else if (index < 3) byte = 0xff;
   		else byte = voltageD;
 
    	bytenum++;
    	if (index == 103) index = 0;
    	 
    }
    
    // On the falling edge of the clock, the output matches the data.
    if (halfcycle & 1)
    	PORTB.0 = (byte >> (halfcycle >> 1)) & 0x01;
    // On the rising edge of the clock, the output is the data inverted.
    else
    	PORTB.0 = (~(byte >> (halfcycle >> 1))) & 0x01;

    halfcycle++; 
}                                                           


//**********************************************************       
//Entry point and task scheduler loop
void main(void)
{  
   initialize();
  
   while(1)
   {
   }//end while(1)
}//end main  


//********************************************************** 
void initialize(void)
{
  //set up the ports 
  DDRB.0=1;	 // PORT.0 and PORT.1 are outputs 
  DDRB.1=1;
  //DDRB.2=0; //PORTB.2 is an input
  PORTB.0=0;
  PORTB.1=0;
  //PORTB.2=0; //no pull-up 
  
  index=0; 
  voltageD=0x00; 
  byte=o;
  halfcycle=0;

  	
  //set up timer 0  
  //TIMSK0=12;		//turn on timer 0 cmp match A and  B ISR
  OCR0A = 32;  	//set the compare to 32 periods
  TCCR0A=0b00000010;		//CTC mode 
  TCCR0B=0b00000111;        //rising edge of external clock 
  TIMSK0=0b00000100;		//enable compare match
   
  //set ADC registers in ADC noise canceler(Idle mode)
  ADMUX=0b01100010;// Vref=1.1v(internalV), select ADCH  select input channel PB4,
  ADCSRA=0b10000110;//enable the ADC, single conversion mode,
          // clk prescaler to 64=150kHZ resolution, no adc conversion complete interrup enable
  
   //turn on the ISR
   #asm ("sei");   
  
}//end initialize