UHF Tag Memory: What are the Key Sections?

A UHF RFID tag is typically divided into four independent storage banks: Reserved, EPC, TID, and User.

Reserved Bank

This 8-byte (4-word) bank holds critical passwords:

• The first 4 bytes (2 words) store the Destroy Password, used to permanently disable the tag (rarely used in typical applications).
• The last 4 bytes (2 words) store the Access Password, required for writing data to the tag or performing lock operations.

The default value for both passwords is 0000000000000000 (Destroy Password) and 0000000000000000 (Access Password).

TID Bank

This 12-byte (6-word) bank is read-only and factory-programmed. It contains the tag's unique identifier and the manufacturer's product class identification number. The TID number is unique to each tag and manufacturer.

EPC Bank

The EPC (Electronic Product Code) bank stores a unique identifier for the tagged object. Unlike the TID, the EPC is user-writable and modifiable.

Its data structure is as follows:

• The first word is a checksum.
• The second word is the Length Control bit (PC), which indicates the length of the actual EPC data.
• Subsequent words store the EPC data.

During an inventory scan, the EPC is displayed based on the length specified by the PC bit.

When writing EPC data, you start at address 1 (referring to the PC bit). The checksum is automatically calculated; you don't need to write it manually.

Calculating the Length Control Bit (PC):

The PC value is derived from the EPC data length.

1. Calculate i: i = (EPC data length in words) * 2.
2. Convert i to hexadecimal.
3. Append "00" to the hexadecimal result to get the PC value.

For example, if your EPC data is 4 words long:

i = 4 words * 2 = 8

8 in hexadecimal is 08.

Append 00: The PC value is 0800.

Writing EPC Data Example:

If your EPC data is "0001" (1 word, 4 digits), ensure the data length is a multiple of 4 bits (or 1 word). Including the PC bit (0800), the total length to write in the software would be 2 words.

Example write command:

Starting Address: 1 (for the PC bit)

Length: 2 (for PC bit + 1 word of EPC data)

Data: 08000001 (where 0800 is the PC and 0001 is the EPC data)

User Bank

The User bank stores user-defined data in hexadecimal format. Its total memory size varies depending on the electronic tag manufacturer.