1.1 Serial Input and Output

The SI/O pin is an open-drain, bidirectional input/output pin used to serially transfer data to and from the device. The SI/O pin must be pulled high using an external pull‑up resistor and may be wire-ORed with any number of other open‑drain or open‑collector pins from other devices on the same bus. The device also utilizes the SI/O pin as its power source by drawing and storing power when the pin is pulled high. The operating voltage range is 1.7V to 3.6V for the AT21CS01 and 2.7V to 4.5V for the AT21CS11.