Reading the serial number is similar to the sequential read sequence but requires use of the specific Device Address and Word Address bytes as specified in Table 1 and Table 2.
Since the Address Pointer of the device is shared between the regular EEPROM array and the serial number block, a dummy write sequence, as part of a random read or sequential read protocol, should be performed to ensure the Address Pointer is set to a known value. Reading the serial number from a location other than the first address of the block will not result in a unique serial number.
Additionally, the word address contains a ‘10’ sequence in bit
A11 and A10 of the word address, regardless of the intended address as depicted in Table 2. If a word address other than ‘10’ is used, then the
device will output undefined data.
When the end of the 128-bit serial number is reached (16 bytes of data), continued reading of the extended memory region will result in an additional 16 bytes of 00h data. Upon reaching the end of the 32-byte extended memory region, the data word address will rollover back to the beginning of the 128-bit serial number. The serial number read operation is terminated when the bus master does not respond with an ACK (it NACKs) during the ninth clock cycle. After the NACK response, the master may send a Stop condition to complete the protocol, or it can send a Start condition to begin the next sequence (see Figure 1).
