AVR-Chat

HI!
My problem with adc is that it does not take samples as I want.I give
a 40HZ sine to differential input of it but the more I increse the
frequency the more periods I get and the resoloution does not
change.In the following result of adc data samples I have 32 samples 
for a 40HZ sine(which sould be more than 80 samples).when I want to
increase the frequency of sampling I increase TCOUNT0  to oveflow
sooner and get more data,but for TCOUNT0=254 it just gives me
zero!!!.Here is the program  and data results.Please guide me.
Thank you...


#include <mega16.h>
#include <stdio.h>
#include <delay.h>
#define nos 7 // Define number of samples
unsigned int current_word; // Global variable for the current ADC output
int i=0,j=0,k=0;
long int sum=0;
int temp[80];
int adc_data[80];
int templ,temph;
// ADC interrupt service routine
interrupt [ADC_INT] void adc_isr(void)
{ 

templ=ADCL; // Get 10 bit data from the ADC register 
/*if((ADCH&0x02)!=0)  
{
#asm
push r16
in r16,0x05
neg r16
out 0x05,r16
pop r16 
#endasm 
}*/ 
temph=ADCH;   
}
// When Timer 0 overflows, conduct this routine
interrupt [TIM0_OVF] void timer0_ovf_isr(void)
{               

#asm
cbi 0x06,7
sbi 0x06,7
#endasm
TCNT0=252;
 putchar(templ);                                         
// putchar(0);
 putchar(temph); 

}
void main(void)
{
DDRA=0x00; // All PORTA bits input
PORTC=0x00; // Set all eight bits of PORTC Low
DDRC=0xFF; // Set all eight bits of PORTC to Output
TCCR0=0x05; // Clock value: 7.2 kHz (7.3728MHZ / 1024) 
TCNT0=0; // Timer/counter 0 initialization
TIMSK=0x01; // Timer interrupt initialization
ADMUX=0xD0;  // Only look at ADC pin 0, ref. 2.56 INTERNAL           
                                                                     
                                                                     
                                                                     
                                                                     
                                                                     
                                                    
ADCSRA=0xEF; // ADC on, prescaler division factor = 128 
[1/(7.3728e6/128)]=138.8e-6___//
// USART initialization
// Communication Parameters: 8 Data, 1 Stop, No Parity
// USART Receiver: Off
// USART Transmitter: On
// USART Mode: Asynchronous
// USART Baud rate: 115200
UCSRA=0x00;
UCSRB=0x08;
UCSRC=0x86;
UBRRH=0x00;
UBRRL=0x03; 
//SFIOR|=0x80;

#asm("sei") // Global enable interrupts
while (1);
}




  -86.8000  -87.2000  -86.4000  -84.2000   86.4000  306.4000  379.8000

  Columns 267 through 273 

  255.8000   16.2000  -86.6000  -87.6000  -88.0000  -73.2000  128.2000

  Columns 274 through 280 

  331.0000  371.8000  221.8000  -17.2000  -86.6000  -87.8000  -87.8000

  Columns 281 through 287 

  -57.8000  167.8000  349.8000  358.4000  185.0000  -46.4000  -87.4000

  Columns 288 through 294 

  -86.0000  -86.8000  -32.4000  205.0000  366.6000  340.2000  147.4000

  Columns 295 through 301 

  -65.0000  -86.4000  -87.6000  -87.0000   -1.2000  239.8000  377.0000

  Columns 302 through 308 

  317.4000  107.2000  -79.2000  -87.8000  -85.8000  -85.6000   35.2000

  Columns 309 through 315 

  271.0000  381.0000  291.0000   65.2000  -87.2000  -86.8000  -86.8000

  Columns 316 through 322 

  -85.0000   77.8000  300.2000  379.2000  261.4000   22.6000  -88.0000

  Columns 323 through 329 

  -89.4000  -86.2000  -75.4000  120.2000  326.0000  374.6000  229.4000

  Columns 330 through 336 

  -11.4000  -88.4000  -88.6000  -86.6000  -59.2000  159.0000  346.8000

  Columns 337 through 343 

  361.8000  193.6000  -40.2000  -87.2000  -88.0000  -89.4000  -38.8000

  Columns 344 through 350 

  197.4000  363.8000  344.4000  155.6000  -61.4000  -85.8000  -87.0000

  Columns 351 through 357 

  -88.6000   -9.2000  233.0000  375.4000  322.6000  115.2000  -76.8000

  Columns 358 through 360 

  -85.8000  -85.2000  -83.6000






and another result:






  -87.6000  -86.8000  -87.4000   14.6000  254.4000  378.4000  306.6000

  Columns 197 through 203 

   89.2000  -82.8000  -87.6000  -87.4000  -86.6000   54.2000  285.4000

  Columns 204 through 210 

  381.6000  279.8000   47.4000  -84.8000  -87.2000  -85.8000  -82.0000

  Columns 211 through 217 

   95.8000  312.0000  379.2000  249.0000    9.2000  -88.0000  -86.6000

  Columns 218 through 224 

  -86.6000  -68.8000  137.2000  336.0000  370.0000  214.4000  -23.4000

  Columns 225 through 231 

  -86.0000  -85.6000  -85.0000  -52.8000  175.4000  353.6000  354.0000

  Columns 232 through 238 

  177.0000  -51.6000  -87.2000  -87.2000  -87.0000  -26.4000  212.6000

  Columns 239 through 245 

  369.6000  335.6000  138.6000  -69.8000  -88.0000  -87.0000  -85.2000

  Columns 246 through 252 

    5.6000  247.0000  378.4000  313.0000   98.6000  -82.8000  -90.2000

  Columns 253 through 259 

  -87.2000  -85.6000   45.2000  279.4000  382.2000  287.0000   56.4000

  Columns 260 through 266