// sr.c
//RLT 10.6.06

#define F_CPU 16000000
#include <util/delay.h>
#include <avr/io.h>

uint8_t out_var;  //global for holding output data

void clk_shift_reg(){
  //toggle bit 1  -- shift register clock
  PORTB = PORTB | 0x02;
  PORTB = PORTB & 0xFD;
//  PORTB = 0x02;
//  PORTB = 0xFD;
  }

void clk_output_reg(){
  //toggle bit 2  -- output register clock
  PORTB = PORTB | 0x04;
  PORTB = PORTB & 0xFB;
//  PORTB =  0x04;
//  PORTB =  0xFB;
  }

void send_data(){
  //send eight bits of data
  uint8_t mask;
  uint8_t i;
  mask = 0x01;               //setup bit mask
//for(i=0; i<=8; i++){       //do for 8 bits
  for(i=0; i<=7; i++){       //do for 8 bits
//clk_shift_reg();           //clock in data bit
    if(out_var & mask)       //test each bit of out_var
      PORTB = PORTB | 0x01;  //set data bit to 1
    else
      PORTB = PORTB & 0xFE;  //set data bit to 0
  mask = mask << 1;          //shift mask left once
  clk_shift_reg();           //clock in data bit
  }//for 
}//send_data

int main()
{
  uint8_t i,j;
  DDRB  = 0x07;                //lower three bits of port b form interface
  PORTB = 0x00;                //initalize to zero
  while(1){ 
    out_var = 0x01;            //start with bit in zero position
    for(i=0; i<=7; i++){       //rotate through all positions
      send_data();             //send 8 bits
      clk_output_reg();        //send data to output register
      out_var = out_var << 1;  //shift the bit left for next time
      for(j=0; j<=5; j++){ _delay_ms(200);}   //wait to make it visible
    }//for i
  }//while
}//main