I was surprised that there is no article about NFC-WI. So I decided to write one for wikipedia. Link: http://en.wikipedia.org/wiki/NFC-WI
Here is content:
NFC-WI is NFC wired interface having 2 wires SIGIN (signal-in) and SIGOUT (signal-out). It is also called S2C (SignalIn/SignalOut Connection) interface. In 2006, ECMA standardized the NFC wired interface with specification ECMA-373 (ECMA,2006).
NFC-WI is an interface between secure element and RF interface of the NFC interface.
It has three modes of operation: off, wired and virtual mode. In off mode, there is no communication with the SE. In wired mode, the SE is visible to the internal NFC controller. In virtual mode, the SE is visible to external RF readers. These modes are naturally mutually exclusive.