Datasheet

157
ATtiny828 [DATASHEET]
8371A–AVR–08/12
Table 55. SPI Pin Overrides
Note: See “Alternative Port Functions” on page 63 for a detailed description of how to define the direction of the user
defined SPI pins.
The following code examples show how to initialize the SPI as a Master and how to perform a simple transmission.
DDR_SPI in the examples must be replaced by the actual Data Direction Register controlling the SPI pins. DD_MOSI,
DD_MISO and DD_SCK must be replaced by the actual data direction bits for these pins. E.g. if MOSI is placed on pin
PB5, replace DD_MOSI with DDB5 and DDR_SPI with DDRB.
Pin Direction, Master SPI Direction, Slave SPI
MOSI User Defined Input
MISO Input User Defined
SCK User Defined Input
SS User Defined Input
Assembly Code Example
SPI_MasterInit:
; Set MOSI and SCK output, all others input
ldi r17,(1<<DD_MOSI)|(1<<DD_SCK)
out DDR_SPI,r17
; Enable SPI, Master, set clock rate fck/16
ldi r17,(1<<SPE)|(1<<MSTR)|(1<<SPR0)
out SPCR,r17
ret
SPI_MasterTransmit:
; Start transmission of data (r16)
out SPDR,r16
Wait_Transmit:
; Wait for transmission complete
in r16, SPSR
sbrs r16, SPIF
rjmp Wait_Transmit
ret