unsigned char SSPI_Transfer(unsigned char data) {
    unsigned char value=0,out=0;
    SPI_CLK = 0;
    SPI_SDO = 0;

    for(unsigned char i=0; i<8; i++) {
        out = ((data>>7-i)&1);
        SPI_SDO = out;
        SPI_CLK = 1;
        SSPI_Delay();

        value = value << 1;
        if(SPI_SDI) {
            value |= 0x01;
        }

        SPI_CLK = 0;
    }

    return value;
}