One-Wire Spy is a useful aid that enables a PC to monitor the communications between a microcontroller and a 1-wire IC from Dallas Semiconductor.The semiconductor manufacturer Dallas Semiconductor offers a series of components that can be controlled, read and programmed by a master device (such as a microcontroller) via a single-wire bus. These ‘1-wire’ devices are mainly available as temperature sensors, battery-management ICs and memory ICs. There is also an identity IC, which contains only an identification serial number. Table 1 summarises the available devices. With a 1-wire bus, it is possible to use not only normal IC packages, but also TO-92, PR-35 and flipchip packages. Dallas Semiconductor even offers ICs in button-cell format, under the name ‘iButton’.