8.4 Serial Number Read

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 6-1 and Table 6-2.

Note: The entire 128-bit value must be read from the starting address of the serial number block to ensure a unique number.

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 6-2. If a word address other than ‘10’ is used, then the device will output undefined data.

Note: If the application desires to read the first byte of the serial number, the word address input would need to be 80h.

When the end of the 128-bit serial number is reached (16 bytes of data), the data word address will roll over 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 8-4).

Figure 8-4. Serial Number Read