24AA256UID-ISLASHSN datasheet(12/28 Pages) MICROCHIP

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24AA256UID

DS20005215A-page 12

 2013 Microchip Technology Inc.

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

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.

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

Standard EEPROM

0000h

6FFFh

7000h

7F79h

7F7Ah

7F7Fh

7FB8h

7FBFh

7FFAh

7FFFh

Unused (Read as 0xFF)

32-Bit Serial Number and Identifiers

Unused (Read as 0xFF)

EUI-48™ Node Address

Unused (Read as 0xFF)

EUI-64™ Node Address

(User – Writable)

Note:

Shaded region is permanently write-protected

Note:

The 32-bit serial number is unique across

all Microchip UID-family serial EEPROM

devices.

Start Address

End Address

Serial Number

Length

0x7FFC

0x7FFF

32 bits

0x7FFA

0x7FFF

48 bits

0x7FF8

0x7FFF

64 bits

0x7FF0

0x7FFF

128 bits

0x7FE0

0x7FFF

256 bits

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