All Nanodes (should!) have a Microchip 11AA02E48 serial EEPROM chip soldered to the underneath of the board (it's the three-pin surface-mount device). This chip contains a unique ethernet address ("MAC address") for the Nanode.
To read the MAC address using this library, use code like this in your sketch:
#include <NanodeUNIO.h>
void setup() { byte macaddr[6]; NanodeUNIO unio(NANODE_MAC_DEVICE);
unio.read(macaddr,NANODE_MAC_ADDRESS,6); }
(If you're using a library like NanodeUIP for networking on your Nanode, you may find that it's already using this library to read the MAC address from the chip.)
The MAC address only takes up 6 bytes in the chip. The other 250 bytes are potentially available for you to use. (By default the top 64 bytes are write-protected, leaving the lower 192 bytes available, but you can disable this as long as you're careful not to overwrite the pre-programmed MAC address.)
See the header file (NanodeUNIO.h) for more information on writing to the chip.
Comments? Suggestions? Contact Stephen Early steve@greenend.org.uk @sde1000 on Twitter