Realising the SPI communication in a multiprocessor system

The SPI communication was originally realised for the fully configurable freely scalable digital audio system. First we used Philipses I²C (inter IC communication), but it was too slow, and the number of the connected devices was limited. With SPI we can connect as many devices as many pins we have on the main microcontroller. The speed of the communication between ICs is much faster thanks for the full duplex proper of the SPI communication.