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RFID tags and memory banks

Before we go deeper into the subject, it is important to highlight that the information presented here was based on the EPC Gen 2 Protocol defined and maintained by GS1. RFID tags, also known as Inlay or Transpreder, store data that will be transmitted to readers during a simple reading or inventory operation. This event is called interrogation. This is when readers “interrogate” the tags that are within the reading radius the antennas, and these, in turn, return the data contained in them according to the request sent by the reader.

This data is stored in 4 memories, being:

  • Reserved memory
  • EPC Memory
  • TID Memory
  • User Memory

When you start your project and select a RFID tag, to find out how much memory there is in the IC of each tag, you can check the specifications page in the chosen database or chip.To help you understand the function of each of the memory banks, we will detail below.

Reserved memory​

This memory bank stores the kill password and the access password (each with 32 bits). The kill password permanently disables the tag (very rarely used) and the access password is set to block and unlock tag recording features. This memory bank is only gradual if you want to specify a particular password. Most users do not use this memory area unless their applications contain confidential data. You cannot store information beyond the two codes. It is important to mention that if an access password is defined and recorded in the tag, reader reading and management software (Middleware) should know this password, otherwise the tags will not be identified or read.

EPC Memory​

This memory bank stores the EPC code, or product electronic code. It has a minimum of 96 bits of gradual memory. EPC memory is usually used in most projects if they only need 96-bit memory. There are some tags that have the ability to allocate more bits for EPC memory from the user memory. EPC memory is your first gradual memory bank. Some tag models that have the EPC bank higher than the 96-bit standard end up not having the user memory bank.

TID memory​

This memory bank is used only to store the number of Chip manufacturer's exclusive tag ID. Normally, this part of the memory cannot be changed, and is used only for reading.

User Memory​

If the user needs more memory than the EPC section has available, certain chips have extended user memory that can store more information. When it comes to user memory, there is no standard in how many memory bits are gravable in each tag. Usually the extended memory is no more than 512 bits, but there are some high memory tags up to 4K or 8K bytes of memory.This memory bank is also rewritten when the chip is EPC Gen2.

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Curiosities​

Much is said about the capacity for recording and rewriting of the RFID tags, and the vast majority of chips on the market allow up to 100,000 recordings, it is possible to record and rewrite the tag up to a maximum of 100,000 times. Remembering that, despite the possibility of rewriting tags, it is important to be aware that most of them have printed identification on their surface and usually represent the same data recorded in the tag. When it is rewritten, you can lose the reference of PRINT x MEMORY, generating identification disorders and application in ongoing projects.

Regardless of the memory bank, data is always recorded and read in decimal hexa, allowing more information to be treated in these small smart chips. For example, when we talk about a 96-bit EPC memory bank, we understand that it is possible to record in this bank up to 24 hexadecimal characters (from 0 to 9 and from A to F).

Is it possible, then, to record my name on the Tag EPC bank? Yes, it is possible, see the example below:

EPC recorded in tag (HEX): 005649414F4E444152464944

After reading this tag, converting the data to text (ASCII), we have: VIAONDARFID

This understanding is of paramount importance for the correct use of tags, since when the project does not use EPC standards, the parameters used and defined during the tag recording need to be shared with reading software and “translation”, otherwise, the final information will be different from expected. In the example above, if the reading software does not know that the recording pattern used was ASCII, it would follow the default translation, trying, at first, to use the TDS Standard (Tag Data Standard) standard and if you do not find a “translated standard” And destination system do not know the pattern used in the recording, it can simply discard this tag. For more information about the TDS standard, go to: https://www.gs1.org/standards/tds

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