168
8025I–AVR–02/09
ATmega48P/88P/168P/328P
When the SPI is enabled, the data direction of the MOSI, MISO, SCK, and SS pins is overridden
according to Table 16-1 on page 168. For more details on automatic port overrides, refer to
”Alternate Port Functions” on page 80.
Note: See ”Alternate Functions of Port B” on page 82 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.
Table 16-1. SPI Pin Overrides
(Note:)
Pin Direction, Master SPI Direction, Slave SPI
MOSI User Defined Input
MISO Input User Defined
SCK User Defined Input
SS
User Defined Input
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