Datasheet

181
7766F–AVR–11/10
ATmega16/32U4
The following code examples show how to initialize the SPI as a Slave and how to perform a
simple reception.
Note: 1. See “Code Examples” on page 8.
17.1 SS Pin Functionality
17.1.1 Slave Mode
When the SPI is configured as a Slave, the Slave Select (SS)
pin is always input. When SS is
held low, the SPI is activated, and MISO becomes an output if configured so by the user. All
Assembly Code Example
(1)
SPI_SlaveInit:
; Set MISO output, all others input
ldi r17,(1<<DD_MISO)
out DDR_SPI,r17
; Enable SPI
ldi r17,(1<<SPE)
out SPCR,r17
ret
SPI_SlaveReceive:
; Wait for reception complete
sbis SPSR,SPIF
rjmp SPI_SlaveReceive
; Read received data and return
in r16,SPDR
ret
C Code Example
(1)
void SPI_SlaveInit(void)
{
/* Set MISO output, all others input */
DDR_SPI = (1<<DD_MISO);
/* Enable SPI */
SPCR = (1<<SPE);
}
char SPI_SlaveReceive(void)
{
/* Wait for reception complete */
while(!(SPSR & (1<<SPIF)))
;
/* Return Data Register */
return SPDR;
}