Hardware Reference
In-Depth Information
//Slave out needs to be enabled by placing the MISO as OUTPUT
pinMode(MISO, OUTPUT);
//Use the AVR Code to turn on slave mode
SPCR |= _BV(SPE);
//Standard Arduino settings for SPI
SPI.setBitOrder(MSBFIRST);
SPI.setDataMode(SPI_MODE0);
SPI.setClockDivider(SPI_CLOCK_DIV4);
//Turn on interrupts for SPI
SPI.attachInterrupt();
Serial.println("Slave Configured");
}
/*AVR SPI interrupt callback
*Process commands sent to slave
* First transfer is the command value
* Second command pushes the value to the master
*/
ISR (SPI_STC_vect)
{
const byte cc = TESTBYTE;
if (SPDR == 0x00) //Only command is 0x00
{
SPDR = 0b11110000; // read byte from SPI Data Register
}
else
{
SPDR = 0b11111111; //Any other command returns 0xff
}
}
void loop()
{
Serial.println("SPI Slave Sketch for testing SPI Master.");
if (digitalRead (SS) == HIGH)
{
SPDR = 0;//When not enable set buffer to 0
}
}
This kind of test requires an Arduino to be configured in slave mode. In order to get the slave to be in SPI slave
mode, you must use AVR code.
SPCR |= _BV(SPE);
enables slave mode for AVR SPI. Additionally, the SPI interrupt
needs to be enabled. It is worth noting that you can use the Arduino
SPI.attachInterupt()
or call the AVR code
directly. In Listing 13-9, you can see that all the function does is call the AVR code.
