Arduino Spi Transfer. Master and slave spi communication between two arduino. The spi port is formed by borrowing the pb2 pb4 fig 1 line of port b.

Spi transfer. On most parts the spi has a second purpose where it is used for in system programming isp. With spi a byte is clocked in at the same time as a byte is clocked out.
The simplest way to use spi transactions involves spibegintransaction right before asserting chip select and spiendtransaction right after releasing it.
But other approaches are possible. I believe arduinos spitransfer waits to receive 8 bits after sending 8 bits. The interconnection between two spi devices always happens between a master device and a slave device. Master and slave spi communication between two arduino.