Chipselect einer SD Karte

Xuint8  sd_send_cmd(Xuint8 Command, Xuint16 ParameterX, Xuint16 ParameterY)

  {

    Xuint8 response;

    XIo_Out32((SPI_BASE_ADDRESS)+ SPI_Slave_Select_Register, CS_LOW);           // CS -> LOW

    delay(50);                                       // wait some CLKs for stable CLK Signal

        spi_send_byte(0x40 | Command);                            //send the command

        spi_send_byte((Xuint8) (ParameterX >> 8));                             //send the MSB of ParamX

        spi_send_byte((Xuint8) (ParameterX));                                    //send the LSB of ParamX

        spi_send_byte((Xuint8) (ParameterY >> 8));                              //send the MSB of ParamY

        spi_send_byte((Xuint8) (ParameterY));                                    //send the LSB of ParamY

        switch(Command)

        {

          case CMD8:

            //when sending the IF cond (CMD8) we must always send

            //the correct CRC

            spi_send_byte(0x87);

            break;

          case CMD0:

            //CMD0 = 0x95 CRC

          spi_send_byte(0x95);

            break;

          default:

            //for all other commands, CRC is ignored in SPI mode.

          spi_send_byte(0xFF);

            break;

        }

    response = spi_read_byte();                              // read the SD response

    XIo_Out32((SPI_BASE_ADDRESS)+ SPI_Slave_Select_Register, CS_HIGH);           // CS -> HIGH

    return response;

  }