24AA256UID Datasheet, PDF (12/28 Pages) Microchip Technology – 256K I2C™ Serial EEPROM

24AA256UID
9.0 PRE-PROGRAMMED SERIAL
NUMBER AND NODE
ADDRESSES
The 24AA256UID is programmed at the factory with
globally unique EUI-48 and EUI-64 node addresses,
and a 32-bit serial number stored in the upper eighth of
the array and permanently write-protected. The
remaining 229,376 bits are available for application
use.
FIGURE 9-1:
MEMORY ORGANIZATION
0000h
Standard EEPROM
(User – Writable)
Unused (Read as 0xFF)
EUI-48™ Node Address
Unused (Read as 0xFF)
EUI-64™ Node Address
Unused (Read as 0xFF)
32-Bit Serial Number and Identifiers
6FFFh
7000h
7F79h
7F7Ah
7F7Fh
7FB8h
7FBFh
7FFAh
7FFFh
Note: Shaded region is permanently write-protected
9.1 32-Bit Serial Number
The 24AA256UID features a unique 32-bit serial
number stored in array locations 0x7FFC through
0x7FFF, as shown in Figure 9-2.
Note:
The 32-bit serial number is unique across
all Microchip UID-family serial EEPROM
devices.
9.1.1
MANUFACTURER AND DEVICE
IDENTIFIERS
In addition to the serial number, a manufacturer code is
stored at location 0x7FFA and a device identifier is
stored at 0x7FFB. The manufacturer code is fixed as
0x29. For the 24AA256UID, the device identifier is
0x48. The ‘4’ indicates the I²C™ family and the ‘8’ indi-
cates a 256 Kbit memory density.
9.1.2
EXTENDING THE 32-BIT SERIAL
NUMBER
For applications that require serial numbers larger than
32 bits, additional data bytes can be used to pad the
provided serial number to meet the required length.
Any data byte values can be used for padding as the
32-bit serial number ensures the extended serial
number remains unique.
The padding can be performed in two ways. The first
method is to pad the data in software by combining the
32-bit serial number from the 24AA256UID with fixed
data. The second method is to extend the number of
bytes read from the 24AA256UID to meet the required
length. Table 9-1 shows example address ranges and
their corresponding serial number lengths.
TABLE 9-1: EXTENDED READ EXAMPLES
Start Address
End Address
Serial Number
Length
0x7FFC
0x7FFA
0x7FF8
0x7FF0
0x7FE0
0x7FFF
0x7FFF
0x7FFF
0x7FFF
0x7FFF
32 bits
48 bits
64 bits
128 bits
256 bits
DS20005215A-page 12
 2013 Microchip Technology Inc.