Before starting to talk about memory banks RFID tags, 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 transporder, store data that will be transmitted to readers during a simple reading or inventory operation. This event is called Interrogation. This is when the readers “interrogate” the tags that are within the reading range of the antennas, and these, in turn, return the data contained therein according to the request sent by the reader.
This data is stored in 4 memory banks, namely:
• Reserved memory
• EPC memory
• TID memory
• User memory
When starting your project and selecting an RFID tag, to find out how much memory is in each tag's IC, you can check the specifications page in the datasheet of the chosen tag or chip. To help understand the function of each of the memory banks, we will detail them below.
Reserved Memory:
This memory bank stores the kill password and the access password (each 32 bits long). The kill password permanently disables the tag (very rarely used) and the access password is set to lock and unlock the tag's recording features. This memory bank is only writable if you want to specify a certain password. Most users do not use this memory area unless their applications contain sensitive data. It cannot store information beyond the two codes. It is important to mention that, if an access password is defined and recorded in the TAG, the reading and reader management software (middleware) must know this password, otherwise the tags will not be identified or read.
EPC Memory:
This memory bank stores the EPC code, or Electronic Product Code. It has a minimum of 96 bits of writable memory. EPC memory is what is typically used in most projects if they only need 96 bits of memory. There are some tags that have the ability to allocate more bits to EPC memory from user memory. EPC memory is your first writable memory bank. Some tag models that have an EPC bank larger than the 96-bit standard end up not having a user memory bank.
TID memory:
This memory bank is only used to store the chip manufacturer's unique tag ID number. Normally, this part of memory cannot be changed, and is used for reading only.
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 bits of memory are writable in each tag. Typically, extended memory is no more than 512 bits, but there are some high memory tags with up to 4K or 8K bytes of memory. This memory bank is also rewritable when the chip is EPC Gen2.
Curiosities:
Much is said about the recording and rewriting capacity of RFID tags, with the vast majority of chips on the market allowing up to 100.000 recordings, that is, it is possible to record and rewrite the tag up to a maximum of 100 thousand times. Remembering that, despite the possibility of rewriting tags, it is important to note that most of them have identification printed on their surface and that, normally, they represent the same data recorded on the tag. When it is re-recorded, the printed reference to memory may be lost, causing identification and application problems in ongoing projects.
Regardless of the memory bank, data is always written and read in hexadecimal, allowing more information to be processed in these small intelligent chips. For example, when we talk about a 96-bit EPC memory bank, we understand that it is possible to record up to a maximum of 24 hexadecimal characters in this bank (from 0 to 9 and from A to F).
