LPC21xx/I2C

The LPC21xx I2C 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 interface will interrupt the CPU when it has finished its operation, meaning you can have an entirely interrupt-driven driver that sends and receives buffers in the background, with little CPU cost.

The interface can act as a master, a slave, or both; to work as a slave you have to tell it what slave address to respond to. It will then interrupt the CPU whenever that address is sent out on the bus, and the interrupt handler can then respond to the incoming request.