DESIGN OF A CUSTOM ASIC INCORPORATING CAN™ AND 1 ...

2.4.3 Unique Address and Device Customization
Within each 1 – Wire® slave device is stored a lasered ROM section with its own
guaranteed unique, 64-bit serial number that acts as its node address. This globally unique
address is composed of eight bytes divided into three main sections: the first byte stores the 8 –
bit family code identifying the device type, the next six bytes store a customizable 48 – bit
individual address, and the last byte contains the CRC data based on the data contained in the
first seven bytes. With a 2 48 address pool, conflicting or duplicate node addresses on the bus are
almost never a problem.
Because 1 – Wire® devices can be formatted with a file directory like a floppy disk, files
can be randomly accessed and changed without disturbing other records. Information is read or
written when the master addresses a slave device connected to the bus, or an iButton is
touched to a probe somewhere along the 1 – Wire® network. The inclusion of up to 64k of
memory in 1 – Wire® devices allows a great deal of information to be stored within the device
[6].
Additionally, 1 – Wire® devices are afforded several types of device customization.
Custom ROM is perhaps the most popular with identification-only devices, but is applicable to
all devices with a 64 – bit ID number. With custom ROM, a pool of 68.7 x 10 9 numbers
(equivalent to 36 bits) is committed to the sole use of a single customer. This type of
customization occurs before packaging, which leads to a fairly long lead-time. For OTP
EPROMs, an alternate customization, called UniqueWare, takes place after packaging. Instead
of modifying the ID number, customer-specified serialization is programmed into EPROM and
then write protected [10].
33