Understanding Tag Memory
Tag data is represented in Hexadecimal format, meaning characters of 0 to 9 and A to F. Each UHF
RFID memory chip consists of 3 sections:
TID –24 characters of unique ROM data. This data cannot be changed and is guaranteed unique.
EPC –24-40 characters of writable data.
User Memory –Varying amounts of additional writeable data variable by chip model.
Memory mapping is organized by Blocks and Word Addresses. A Word is 16 bits, also known as 2
bytes and appears as 4 hex characters. The last 4 characters in the example Tag read above of 5242 is
16 bits, aka 2 bytes or 1 Word.
Viewing the table below, think of the mapping as streets and house addresses. In this small town,
we’ve only got 4 streets, Block 00, 01, 02, and 03. Each house (address) has a function or contains
Tag data.
Block 00 allows the functions of killing a Tag such that it is rendered inoperable, or setting a
password so that a Tag can only be re-programmed if that password is known. As of this writing, we
have not included the Kill Tag option, only the password option exists. Default password is set to
00000000. Setting a password only limits the reprogramming of Tag data. Tag data can always be
read regardless of whether a password is set or not. If you wish to set a password, it is critical that
each password is documented. If forgotten, there is no way to recover that password.
Block 01 has 8 addresses, of which 00 and 01 are functions, not accessible by the user. CRC in
address 00 is a check sum to ensure data is not corrupt. Protocol Control tells us if User Memory
contains data. A Tag reporting 3000 tells us the user memory has not been programmed, while 3400
alerts us that there is more data present in User Memory. Note that sometimes these are represented
as 5000 and 5400 when EPC length is increased to 40 characters. Notice addresses 02 to 07, EPC
data. This range encompasses 6 addresses, each being 4 characters, and 4 x 6 = 24, which is the
length of our EPC data in the example above. If we were to look into address 07 only, we’d see the
last 4 characters of 5242, also known as the last Word.
Block 02 is the TID data, ROM, always unique, cannot be altered. If you’d like to operate with TID
data, use the pulldown menu in the Inquiry Area section, choose TID and Set.
Block 03 begins User Data, which is basically extra data beyond the 24 characters of EPC. If you’d
like to read or write User Data, set the Inquiry Area to User Data first, and Set. Some memory chips
have zero User Data, another may have 512 bits, and divided by 4 would equal 128 characters of data
divided into 32 Words (4 data characters). See the section Tag Memory Chip Options on page 10.
