The UNI/O serial EEPROM is a single I/O EEPROM device that has been developed by Microchip. The EEPROM has been developed to work on the UNI/O Bus, a propriety single I/O bus protocol, also developed by Microchip. The bus combines the clock and data lines into a single bit stream using the Manchester Encoding technique.

- MCU establishes the data rate with an 8-bit start header.
- UNI/O device will time out and go to standby if an expected transition is not seen.
- The EEPROM will synchronize to the MCU data rate as long as the clock frequency is between 10 KHz to 100 KHz.

Both the master and slave can operate as transmitter or receiver but the master determines which mode is active.

Advantages

- Saves pins on the microcontroller: Only uses a single I/O port (see Figure 1)
- Save board space: Available in 3-pin package
- Small connectors: 3-pin or 2-pin connection (see Figure 2)
- Clock easily extracted from data stream
- Follow Master data rate change, not fixed data rate
- Multiple Slaves:
1. Each UNI/O device syncs to MCU data rate
2. Resynchronization circuitry allows slaves to remain in sync with Master

Applications
Any place where you need fewer I/O and to save board space:

- Authentication: Serial EEPROM used in Printer Cartridges, Medical Devices & Batteries
- Calibration: Instrumentation Equipment, Medical Glucose Strips, Insulin Pumps
- Identification: PC Cards, Smart Cards
- Data Logging: Alarm Systems
- Configuration Settings, Usage Records: Home Appliances, Medical Device, Consumer Electronics