Beschleunigungssensor ADXL345 Probleme bei der SPI Kommunikation

#include <avr/io.h>

//#define F_CPU 8000000UL

#define F_CPU 3686400UL

#include <util/delay.h>

#include "usi_isp.c"

void uart_init(void)   

{

   #define BAUD 9600

   #include <util/setbaud.h>

  /* Set baud rate */

  UBRRH = UBRRH_VALUE;

  UBRRL = UBRRL_VALUE;

     #if USE_2X

   UCSRA |= (1 << U2X);

   #else

   UCSRA &= ~(1 << U2X);

   #endif

  //  Enable receiver and transmitter 

  UCSRB = (1<<RXEN)|(1<<TXEN);

  // Set frame format: 8data, 

  UCSRC = (3<<UCSZ0);

}  

int main (void)

{

  uart_init();

  spi_init();

  while (1)

  {                         

    UDR = spi_read_byte(0x00);

    _delay_ms(100);

  }

return 0;

}

#include <avr/io.h>

#include <util/delay.h>

//#define SPI_CLK 12500   // spi clock 

#define CS_PIN PB4    // chip select pin

#define CS_REG PORTB  // chip select register

#define SPI_DEVICE_T_DELAY 1

// SPI port and pin definitions.

#define SPI_PORT  PORTB  //!< SPI port output register.

#define SPI_PIN_REG  PINB  //!< SPI port input register.

#define SPI_DIR_REG  DDRB  //!< SPI port direction register.

#define SPI_CLOCK_PIN  PB7  //!< SPI clock I/O pin.

#define SPI_DATAIN_PIN  PB5  //!< SPI data input pin.

#define SPI_DATAOUT_PIN  PB6  //!< SPI data output pin.

#define SPI_CS_PIN  PB4    //!< SPI Cock Select pin.

void spi_init(){

  // outputs

  SPI_DIR_REG |= ( 1<< SPI_CLOCK_PIN | 1<< SPI_CS_PIN );

  // inputs

  // when 4  wire mode is choosen, define DI- and DO- pin mode here

}

void spi_chip_enable()

{

  CS_REG &= ~(1<<CS_PIN); // ~CS = 0 -> enable slave device;

  _delay_us(10);  //später durch _delay_cycles ersetzen

}

void spi_chip_disable()

{

   // _delay_us(SPI_DEVICE_T_DELAY);  // see ADXL345 Data Sheet Figure 37 to 39

  _delay_us(10);  //später durch _delay_cycles ersetzen!

  CS_REG |= (1<<CS_PIN); // ~CS = 1 -> disable slave device;

}

//**************************************************************

//***********[ READ BYTE FROM SPI without USI ]*****************

//**************************************************************

unsigned char spi_read_byte( unsigned char address ){

  unsigned char cnt, data; 

 //******************** transmitt byte *********************************

  // configure IO pin functions (not nessesary for 4-wire spi but for 3 wire mode)

  SPI_DIR_REG |= ( 1<< SPI_DATAOUT_PIN);  //!< USI port direction register

  // 0x80: read(single byte) mode

  data = ( 0x80 | (address & 0x3F) );

  cnt = 0;

  spi_chip_enable();

  if( ( (data << cnt) & 0x80 ) )    

    SPI_PORT |= (1<< SPI_DATAOUT_PIN);  //  

  else

    SPI_PORT &= ~(1<< SPI_DATAOUT_PIN);  // 

  _delay_ms(1); // t_delay (ADXL345)

  //  generate SLK

  SPI_PORT &= ~(1<< SPI_CLOCK_PIN);  //  

  _delay_ms(20); //  _delay_us(1000000/(2*SPI_CLK));

  SPI_PORT |= (1<< SPI_CLOCK_PIN);  //

  _delay_ms(20); //  _delay_us(1000000/(2*SPI_CLK));

  cnt++;

  do{

    // transmitt data

    if( ( (data << cnt) & 0x80 ) )    

      SPI_PORT |= (1<< SPI_DATAOUT_PIN);  //  

    else

      SPI_PORT &= ~(1<< SPI_DATAOUT_PIN);  // 

    //  generate SLK

    SPI_PORT &= ~(1<< SPI_CLOCK_PIN);  //  

    _delay_ms(20); //  _delay_us(1000000/(2*SPI_CLK));

    SPI_PORT |= (1<< SPI_CLOCK_PIN);  //

    _delay_ms(20); //  _delay_us(1000000/(2*SPI_CLK));

    cnt++;

  }while ( cnt < 8 ); // stop when 8bits are transmitted

  //******************** receive byte *******************************

  // configure IO pin functions (not nessesary for 4-wire spi but for 3 wire mode)

  SPI_DIR_REG &= ~( 1<< SPI_DATAIN_PIN);  // 

  SPI_PORT |= ( 1<< SPI_DATAIN_PIN);

  cnt = 0;

  data = 0;

  do{   

    //  generate SLK

    SPI_PORT &= ~(1<< SPI_CLOCK_PIN);

    _delay_ms(20); //  _delay_us(1000000/(2*SPI_CLK));

    SPI_PORT |= (1<< SPI_CLOCK_PIN);  //

     // read data from pin DI (sample on rising edge)

    if( SPI_PIN_REG & ( 1<< SPI_DATAIN_PIN) ) 

     data |= ( 1 << cnt );

    _delay_ms(20); //  _delay_us(1000000/(2*SPI_CLK));

     cnt++;

   }while ( cnt < 8 ); // stop when 8 bits are transmitted

  spi_chip_disable();

return data;

}