Types of Serial EEPROM Chips

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There are several types of Serial EEPROMs, but most of them fall into either a 2-wire or 3-wire interface category. Usually, the 3-wire devices require an addition wire (beyond the 3 for data transfer) for each chip to be used. The 2-wire interface, called I2C or IIC or "I squared C" uses only two wires, regardless of how many chips are attached. I2C is a trademard of Philips. The three wire interfaces include SPI and Microwire, which is a trademark of National Semiconductor.
As the pressure on engineers to make products smaller has grown, semiconductor manufacturers have introduced several new interfaces, usually aimed at lower a product's size and cost... and undoubtedly many more will appear in the future.
As a practical matter, the code offered below only works with the Microwire 3 Wire interface, and is specifically intended to work with the 93C46, which is a standard part available from a variety of distributors.