SPI problems with ATMEGA328 as Master

Question

I am trying to connect ATMEGA328p as master to X25020 EEPROM as slave.

here is my code

void spi_master_init()
{
   DDRB = ( (1<<PB2) | (1<<PB3)  | (1<<PB5) );   // /SS as output, MOSI and SCK as output
   SPCR = ( (1<<SPE) | (1<<SPR1) | (1<<MSTR)); //SPI Enable, fosc/64, Master mode
}


void spi_slave_init()
{
   DDRB = 0<<PB4;     //MOSI as input
   SPCR = 1<<SPE ;
}


void SPI_Tx(char data)
{
   SPDR=data;
   while( !(SPSR & (1<<SPIF)) );   //wait until SPIF flag is set, to indicate transmission is complete
}

char SPI_Rx()
{
   char Rx_char;   
   while( !(SPSR & (1<<SPIF)) );
     Rx_char= SPDR;

   return Rx_char;
}

void write_to_slave()
{
   PORTB|=1<<PB2;    //take /CS on slave LOW
   SPI_Tx(0x06);  //WREN write enable command
   PORTB&=0<<PB2;    //take /CS on slave HIGH

   PORTB|=1<<PB2;    //take /CS on slave LOW
   SPI_Tx(0x02);  //WRITE instruction
   SPI_Tx(0x20);  //Address to write data to
   SPI_Tx(0x01);  //Data to be written
   PORTB&=0<<PB2;    //take /CS  on slave HIGH
}

char read_from_slave()
{
   char recvd_char;
   PORTB|=1<<PB2;    //take /CS on slave LOW
   SPI_Tx(0x03);  //READ instruction
   SPI_Tx(0x20);  //Address to be read from

   recvd_char = SPI_Rx();
   return recvd_char;
}

int main (void)
{
   DDRC=0xff;   //PORTC as output


   char recvdchar=0;

   spi_master_init();
   spi_slave_init();

   write_to_slave();

   recvdchar=read_from_slave();

   if(recvdchar==0x01)
    PORTC=1<<PC0;
}

The idea is to write 0x01 to address 0x20 on the slave chip, and read it back, if successfully read light up an LED on PC0.

Somehow i cant see why it does not work, I checked connections of slave chip, seem to be fine.

followed datasheet instructions to talk to the slave chip.

http://pdf.datasheetcatalog.com/datasheets/70/290256_DS.pdf

Answer 1

You need to add a dummy write to your RX function to provide the clock (clock is only generated by the master). A assume that the your init code and the eeprom communication protocol is correct.

char SPI_Rx()
{
   char Rx_char;   
   SPI_Tx(0);
   while( !(SPSR & (1<<SPIF)) );
     Rx_char= SPDR;

   return Rx_char;
}