Question

I’m currently investigating how NFC works, doing some tutorials, making some small apps to read/write/do_things when detect RFID tags…

But i’m currently wondering, how does the card emulation works ? I mean i know the phone support this mode. (cf :
http://www.nearfieldcommunicationsworld.com/2011/02/13/35913/uncovered-the-hidden-nfc-potential-of-the-google-nexus-s-and-the-nokia-c7/ )

But what if the phone is off ? It seems the component used in the Nexus S for example supports “Battery low / Battery off” mode. But how does it work ? (http://www.nxp.com/documents/leaflet/75016890.pdf).

Thanks.

Clement.M

Answer 1

I might be guessing here but normally the key to NFC (at least with rfid cards) is that the base station provides the device with the power needed to transmit the data….so maybe once the data is set there is no need for mobile battery…

Edit: just saw it in the datasheet. The Chip supports “Power by field mode” so like a RFID card your device is powered by the electromagnetic field the base station emits. Probably there is a non-volatile memory inside the chip which does not need any constant power and can then be used as memory of the field powered device.