Datasheet

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;
}
Note: 1. See About Code Examples.
Related Links
Pin Configurations on page 13
Alternate Functions of Port B on page 81
Alternate Port Functions on page 78
About Code Examples on page 19
22.3. SS Pin Functionality
22.3.1. 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 other pins are inputs.
When SS is driven high, all pins are inputs, and the SPI is passive, which means that it will not receive
incoming data. The SPI logic will be reset once the SS pin is driven high.
The SS pin is useful for packet/byte synchronization to keep the slave bit counter synchronous with the
master clock generator. When the SS pin is driven high, the SPI slave will immediately reset the send and
receive logic, and drop any partially received data in the Shift Register.
22.3.2. Master Mode
When the SPI is configured as a Master (MSTR in SPCR is set), the user can determine the direction of
the SS pin.
Atmel ATmega32A [DATASHEET]
Atmel-8155I-ATmega32A_Datasheet_Complete-08/2016
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