<div class="htmlview paragraph">Boeing's Self-Timed Parallel Interface (SPI) Controller implements the synchronous PI bus backplane as well as an asynchronous self-timed backplane. The asynchronous mode implements the PI bus protocol while utilizing a self-timed transfer scheme. This scheme eliminates the complex clocking scheme of the synchronous backplane, supports decentralized systems, is technology independent, and supports very high data transfer rates. The technology independence of the SPI bus controller means that the transfer rate on the backplane is as fast as the technology will allow for the active modules on the backplane.</div>