SPIWARE

The GPIO expander over SPI communication

Protocol 0.1

It's is a implementation to a SPI "bridge slave mode" to ATMEGA328p.

Protocol byte frame

MODE	VALUE	PORT ADDR	PIN ADDR
SPI_B7	SPI_B6	SPI_B5 | SPI_B4 | SPI_B3	SPI_B2 | SPI_B1 | SPI_B0

• SPI_B7

  It's is the access mode to the regiters LOW (0) to read and HIGH (1) to write

• SPI_B6

  It's is the bit value to be write on register

• SPI_B[5-3]

  Register address [ PORT | DDR ]

• SPI_B[2-0]

  Register slot address

PORT mapping (ATMEGA328p only)

REGISTER	ADDR
DDRB	0 0 1
DDRC	0 1 0
DDRD	0 1 1
PORTB	1 0 0
PORTC	1 0 1
PORTD	1 1 0

Raw bit examples

• Write 1 on PB7

  /*
   * We need to set
   * SPI_B7 = 1       --> Write mode
   * SPI_b6 = 1       --> write '1'
   * SPI_B[5-3] = 100 --> PORTB
   * SPI_B[2-0] = 111 --> 7 in binary
   */
  
  /* binary way */
  command = 0b11100111;
  /* hex way */
  command = 0xE7

• Read PD7

  /*
   * We need to set
   * SPI_B7 = 0       --> Read mode
   * SPI_b6 = 0       --> 0
   * SPI_B[5-3] = 110 --> PORTD
   * SPI_B[2-0] = 110 --> 7 in binary
   */
   
  /* binary way */
  command = 0b00110110;
  /* hex way */
  command = 0x36;

• Read ADC 1

  To access the Analogic Digital Converter (ADC) the command should in READ MODE and set 1 in value bit (SPI_B6) and do not specify any PORT. so the command to read ADC should start with 01000_ _ _ the last 3 bits is the ADC number.

  /* binary way */
  command = 0b01000001;
  // hex way
  command = 0x41;
  
  /*
   * To make easier you can do.
   */
   #define ANALOG_CMD = 0x40
   command = ANALOG_CMD | 0x01