atmega3250v-8auatmega325v-8ai ATMEL Corporation, atmega3250v-8auatmega325v-8ai Datasheet - Page 151

• Manufacturer Part Number: atmega3250v-8auatmega325v-8ai
• Description: Atmega3250 8-bit Microcontroller With In-system Programmable Flash
• Manufacturer: ATMEL Corporation

19.3
19.3.1
2570L–AVR–08/07
SS Pin Functionality
Slave Mode
The following code examples show how to initialize the SPI as a Slave and how to perform a
simple reception.
Note:
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
Assembly Code Example
C Code Example
SPI_SlaveInit:
SPI_SlaveReceive:
void SPI_SlaveInit(void)
{
}
char SPI_SlaveReceive(void)
{
}
; Set MISO output, all others input
ldi
out
; Enable SPI
ldi
out
ret
; Wait for reception complete
sbis SPSR,SPIF
rjmp SPI_SlaveReceive
; Read received data and return
in
ret
/* Set MISO output, all others input */
DDR_SPI = (1<<DD_MISO);
/* Enable SPI */
SPCR = (1<<SPE);
/* Wait for reception complete */
while(!(SPSR & (1<<SPIF)))
/* Return Data Register */
return SPDR;
1. See
;
r17,(1<<DD_MISO)
DDR_SPI,r17
r17,(1<<SPE)
SPCR,r17
r16,SPDR
“About Code Examples” on page
(1)
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ATmega325/3250/645/6450
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