DOC7707 datasheet(141/307 Pages) ETC1

141 / 307 page

141

7707F–AVR–11/10

AT90USB82/162

The following code examples show how to initialize the SPI as a Slave and how to perform a

simple reception.

Note:

1. See “About Code Examples” on page 7.

16.1

SS Pin Functionality

16.1.1

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

other pins are inputs. When SS is driven high, all pins are inputs, and the SPI is passive, which

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

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;

}

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