LPC21xx/SPI

The LPC21xx SPI interface lets you start it sending or receiving a byte, then leave it to get on with it while the CPU does other work. This is much nicer than "bit banging", where one uses a GPIO line to do serial I/O, with the software having to send each bit in turn.

The SPI interface will interrupt the CPU when it has finished its operation, meaning you can have an entirely interrupt-driven SPI driver that sends and receives buffers in the background, with little CPU cost. This will be great for applications that use things like large SPI FLASH ROMs and have to move a lot of data about.