The invention relates generally to serial communications buses and relates more particularly to single-wire asynchronous serial communications buses.
In order to simplify modern miniature apparatus, it is desirable to have as few as possible physical connections between different ICs or modules comprising the miniature device. Then a smaller number of pins could be sufficient (which has a favorable price impact), and less printed circuit board area required for wiring. At the same time, it is desirable to operate at the lowest possible power consumption, so that the apparatus will be functional for as long as possible on the same set of batteries or a single charge of the batteries.
Such pressures—minimizing pin count, minimizing connections, and minimizing power consumption—present themselves with many modern apparatus, including such products as notebook computers, smart batteries, cell phones, and personal digital assistants. It is also desirable that any communications bus be simple to use. If the bus defines one device as a “master” and others as “slaves” then it is desirable that the bus permit a slave to request service from the master device.
It is also desirable to have a bus that operates in such a way that any conflict between line drivers in bus devices is prevented. For example if there are “master” and “slave” devices, it is desirable to prevent conflicts where one device attempts to drive the bus high and another device attempts to drive the bus low.
A variety of single-wire serial buses have been proposed, among them “Single wire data communication method,” U.S. Pat. No. 6,108,751; “Single wire communication system,” U.S. Pat. No. 5,864,872; “Communications network, a dual mode data transfer system therefor,” U.S. Pat. No. 5,579,299; “Method and apparatus for storing information on a replaceable ink container,” U.S. Pat. No. 6,065,824; “Parasitically powered microprocessor capable of transmitting data over a single data line and ground,” U.S. Pat. No. 6,412,072; and “Serial bus system with a single-wire line,” U.S. Pat. No. 5,412,644. Other serial buses which have been proposed include “Two-wire bus-system comprising a clock wire and a data wire for interconnecting a number of stations,” U.S. Pat. No. 4,689,740.