|II01 is an optocoupler isolator for the Philips bi-directional I²C-bus serial interface, so that ground loops and high frequency interference can be avoided when I²C compatible units, like audio equipment and FM tuners, are controlled from a PC.
The 9-pin SUB-D connectors on II01 is pin compatible with the ICA90 ISA I²C-bus controller card from Calibre UK Limited.
The I²C-bus is a 2-wire interface with a clock line, SCL, and a data line, SDA, that have pull-up resistors to 5 V and can be pulled low by any device connected to the bus.
II01 has 2 optocouplers (one in each direction) for each of the 2 lines and the necessary control logic to prevent system lock-up.
The II01 have been tested with a 100 kbits/s I²C-bus, but is probably fast enough to be used in a 400 kbits/s system.
The I²C-bus is fully documented in the documents "The I²C bus and how to use it" and "AN10216-01, I²C Manual" from NXP.