RFID basics

Introduction

In this article you can find some basic info about RFID industry

Standards and protocols

Read about GSIN top level shipment id: GS1_General_Specifications

EPC™ Radio- Frequency Identity Protocols Generation-2 UHF RFID

Image 6.19 is especiaslly interesting.

EPC Tag Data Standard

TDS_1_9_Standard

Table 14.5.2.1.SSCC-96 Coding Table

Tag Memory Map

Generally speaking, the memory of a tag is split into four:

Reserved memory

EPC

TID

User Memory

TID

The TID or Tag Identifier is 20 bytes or 160 bits. Every RFID tag has a unique TID. The TID is not editable but in some cases there can be variable values withing the same tag.

As an example we can take a look at Alien Higgs-4 datasheet and check the memory map:

TID means Tag identification memory, in a Gen 2 RFID tag, this consists of memory about the tag itself, such as the tag ID

Alien Higgs-4 Memory map

HEX to Decimal

Notice that Address order is from bottom to top.

First 32 bits of TID (00h - 1Fh) are ROM and last 96 bits of TID (60h - BFh) are ROM-NVM and there you can find altering hexes.

So if you want to be on the safe side and read only the Unique part of TID you should use bits from 32 to 96 (20h - 5Fh).

For example, if you are using 16 bit Words, you should set your software settings to read words 3, 4, 5 and 6.

Reserved Memory:

This memory bank stores the kill password and the access password (each are 32 bits).

The kill password permanently disables the tag (very rarely used), and the access password is set to lock and unlock the tag's write capabilities. 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 besides the two codes.

EPC Memory

The Electronic Product Code™ (EPC) is syntax for unique identifiers assigned to physical objects, unit loads, locations, or other identifiable entity playing a role in business operations.

This memory bank stores the EPC code, or the Electronic Product Code. It has a minimum of 96 bits of writable memory.

The EPC memory is what is typically used in most applications if they only need 96 bits of memory. There are some tags that have the capability of allocating more bits to the EPC memory from the user memory.

EPC memory is your first writable memory bank.

EPC memory block

EPC memory block contains EPC itself, CRC and PC

CRC stands for Cyclic Redundancy Check. CRC-16 means that the lenght is 16 bits.

PC stands for Protocol Control and it defines how many bits of EPC number are send to the reader (and other things to be discussed below).

For example you can have enough chip memory in your tag to have 128 bits of EPC number. But you need to send only 96 bits. Changing PC value will solve the issue.

Further Reading

Tag Encoding Standards

NOTE #1: Company Prefix and Serial number with Extension digit have combined length of 58 bits but the distribution of memory between them can be different for each specific project.

Company Prefic can have from 20 to 40 bits length.

Serial nubmer plus Extension digit can have from 38 to 18 bits length respectively.

NOTE #2: The Extension digit is positoined differently in Barcode and in EPC. In the barcode it is printed before the Company code but in the EPC it is between the Company code and the Serial number.