1-Wire bus is really interesting piece of electronic design by Dallas Semiconductor. It provides two-way serial connection on 1 wire (technically two, of course – don’t forget the common ground). There are a lot of devices use 1-Wire interface, from simple thermometers to ID buttons with memory. Fredrik Lindberg shows how to make an 1-Wire bus master device which can communicate through IPv6. His device is based on an Atmel AVR ATmega644 and the ENC28J60 Ethernet controller from Microchip. With this you can address your 1-Wire devices through Ethernet connection.
Microprocessor’s registers seems to be a simple F/F, but they aren’t. There are a lot of interesting details and tricks under the hood. Ken Shirrif shows them “to the silicon” in his brilliant reverse engineering article about the 8085’s registers.