MCP23S17 lesen geht nicht (AVR SPI)

#define SPI_PORT PORTB

#define SPI_DDR  DDRB

#define SPI_CS   PB1

#define SPI_SLAVE_ID    0x40

#define SPI_SLAVE_ADDR  0x00      // A2=0,A1=0,A0=0

#define SPI_SLAVE_WRITE 0x00

#define SPI_SLAVE_READ  0x01

#define IODIRA 0x00

#define IODIRB 0x01

#define IOCONA 0x0A

#define IOCONB 0x0B

#define GPPUA  0x0C

#define GPPUB  0x0D

#define GPIOA  0x12

#define GPIOB  0x13

void init_SPI() {

  SPI_DDR = (1 << PB3) | (1 << PB5) | (1 << SPI_CS);

  SPI_PORT |= (1 << SPI_CS);

  SPCR = (1 << SPE) | (1 << MSTR);

  SPSR |= (1 << SPI2X);

  SPI_Write(IOCONA, 0x28); // I/O Control Register: BANK=0, SEQOP=1, HAEN=1 (Enable Addressing)

  SPI_Write(IODIRA, 0x00);   // GPIOA As Output

  SPI_Write(IODIRB, 0xFF);   // GPIOB As Input

  SPI_Write(GPPUB, 0xFF);    // Enable Pull-up Resistor on GPIOB

  SPI_Write(GPIOA, 0x00);    // Reset Output on GPIOA

}

void awaitTransmission() {

  while (!(SPSR & (1 << SPIF))) ;

}

void SPI_Write(unsigned char addr, unsigned char data) {

  SPI_PORT &= ~(1 << SPI_CS);

  SPDR = SPI_SLAVE_ID | ((SPI_SLAVE_ADDR << 1) & 0x0E) | SPI_SLAVE_WRITE;

  awaitTransmission();

  SPDR = addr;

  awaitTransmission();

  SPDR = data;

  awaitTransmission();

  SPI_PORT |= (1 << SPI_CS);

}

unsigned char SPI_Read(unsigned char addr) {

  SPI_PORT &= ~(1 << SPI_CS);

  SPDR = SPI_SLAVE_ID | ((SPI_SLAVE_ADDR << 1) & 0x0E) | SPI_SLAVE_READ;

  awaitTransmission();

  SPDR = addr;

  awaitTransmission();

  SPDR = 0x00; // dummy data

  awaitTransmission();

  SPI_PORT |= (1 << SPI_CS);

  return (SPDR);

}