RFID Basics: How to Read and Write Tags
Radio frequency identification, or RFID, is built around a simple idea: small tags store digital data, and readers capture or update that data wirelessly. While the concept is straightforward, many real-world RFID challenges stem from misunderstanding how reading and writing RFID tags actually works.
This guide explains the RFID read write process in practical terms. It covers what data lives on a tag, how memory banks are structured, how to program RFID tags correctly, and which mistakes to avoid when encoding at scale. Whether you are deploying RFID for asset tracking, inventory management, or manufacturing workflows, understanding these fundamentals helps ensure reliable performance and long-term system flexibility.
- What Does It Mean to Read an RFID Tag?
- What Does It Mean to Write to an RFID Tag?
- What Data Is Stored on an RFID Tag?
- What You Need to Read and Write RFID Tags
- How the RFID Read and Write Process Works
- Can RFID Tags Be Rewritten or Locked?
- RFID Encoding Best Practices
- Common Mistakes When Writing RFID Tags
- Summary: Reading vs Writing RFID Tags
- A Practical Note from the Field
What Does It Mean to Read an RFID Tag?
Reading an RFID tag means wirelessly retrieving the data stored on the tag’s memory. When an RFID reader emits radio waves, nearby tags harvest that energy, power up briefly, and respond by transmitting their stored information back to the reader.
In most systems, the RFID reader captures a unique identifier called the EPC, or Electronic Product Code. This identifier is then passed to software, where it is associated with richer information such as product descriptions, locations, or transaction history. Importantly, the bulk of business data usually lives in software databases, not directly on the RFID tag.
From an operational standpoint, reading is passive for the tag. The reader does not alter tag data during a read event. This distinction matters when designing workflows that involve both scanning and encoding.
What Does It Mean to Write to an RFID Tag?
Writing to an RFID tag, often called encoding, means permanently or semi‑permanently storing data in one or more of the tag’s memory banks. During a write operation, the reader sends a command that updates specific memory locations on the tag.
Writing is more controlled than reading. It typically requires closer proximity, stronger signal integrity, and correct configuration of the reader and software. Many RFID deployments only write data once, such as encoding a unique EPC at the point of manufacture or commissioning.
Understanding how to program RFID tags correctly is critical. Improper encoding can lead to duplicate identifiers, unreadable tags, or data that does not align with backend systems.
What Data Is Stored on an RFID Tag?
Not all data stored on an RFID tag is the same. Modern RFID tags contain multiple memory areas, each designed for a specific purpose. These areas are known as RFID tag memory banks.
Most applications interact with only one memory bank, but understanding the full structure helps you make better design decisions and avoid unnecessary complexity.
EPC Memory
EPC memory is the most commonly used memory bank. It stores the Electronic Product Code, which uniquely identifies the tagged item. EPCs are typically 96 bits long, though longer formats exist for specialized use cases.
In supply chain, retail, and asset tracking systems, the EPC acts as a license plate. The tag transmits the EPC, and software looks up associated data elsewhere. This approach keeps tag memory simple and scalable.
TID Memory
TID, or Tag Identifier memory, is set by the chip manufacturer and cannot be modified. It includes information about the chip model and a unique serial number.
Because TID memory is read‑only, it is often used for authentication, anti‑counterfeiting, or verification scenarios. Most standard RFID applications do not rely on TID for daily operations, but it can be useful in higher‑security environments.
User Memory
User memory is optional and varies widely between tag models. This memory bank allows users to store custom data directly on the tag, such as batch numbers, maintenance dates, or configuration flags.
While user memory adds flexibility, it also introduces complexity. Writing and reading larger data blocks takes more time and requires careful formatting. In many systems, user memory is used sparingly, if at all.
What You Need to Read and Write RFID Tags
A functional RFID system requires both hardware and software components working together. While reading and writing RFID tags rely on similar equipment, encoding often demands higher precision.
At a high level, you need three core elements: tags, readers with antennas, and software.
RFID tags must support the memory structure and rewrite capability your application requires. Not all tags include user memory, and not all tags support multiple write cycles.
RFID readers and antennas handle the wireless communication. Modern readers support adjustable power levels, advanced filtering, and precise write controls, which are especially important for encoding stations.
RFID software acts as the control layer. It determines which memory bank is accessed, what data is written, and how read events are processed. Flexible software also allows you to validate data before encoding and prevent errors such as duplicate EPCs.
How the RFID Read and Write Process Works
The RFID read/write process follows a predictable sequence, regardless of specific hardware brands or software platforms.
First, the reader energizes nearby tags using radio frequency signals. Next, the reader issues a command, either to read data or to write data to a specific memory bank. The tag responds by transmitting data back or confirming that a write operation was successful.
In encoding workflows, additional safeguards are often added. These may include read‑after‑write verification, database checks to ensure EPC uniqueness, and controlled antenna fields to prevent accidentally writing to multiple tags at once.
Understanding this process helps teams design reliable encoding stations and troubleshoot issues when tags fail to read or write consistently.
Watch the quick video below to see an example of writing to and reading a UHF RFID tag.
Can RFID Tags Be Rewritten or Locked?
Most modern UHF RFID tags are rewritable, but there are limits. Tags support a finite number of write cycles, often in the range of 10,000 to 100,000 writes per memory location. In practice, most applications write data once or only a few times, well within these limits.
Tags can also be locked. Locking prevents further changes to specific memory banks, such as EPC or user memory. This is useful when data must remain permanent, or only re-written with a specific unlock key after commissioning.
RFID Encoding Best Practices
Following RFID encoding best practices reduces errors and improves system longevity. One key principle is to encode only the data you truly need on the tag. Overloading user memory often adds complexity without clear benefits.
Another best practice is to standardize EPC formats. Consistent length and structure make downstream processing easier and reduce integration challenges.
Validation is equally important. Read‑after‑write verification ensures that encoded data matches expectations before tags enter circulation. Controlled encoding environments, such as fixed stations with shielding or tuned antennas, further reduce the risk of miswrites.
Common Mistakes When Writing RFID Tags
Many RFID issues trace back to avoidable encoding mistakes. One common error is writing the same EPC to multiple tags due to poor software checks. This creates duplicate identities that undermine system accuracy.
Another frequent issue is attempting to write to the EPC or User memory bank without confirming tag capacity. Not all tags support the same memory sizes, and failed writes can slow down operations.
Finally, teams sometimes underestimate the importance of antenna placement and power tuning. Excessive power can cause unintended writes to nearby tags, while insufficient power leads to inconsistent results.
Summary: Reading vs Writing RFID Tags
Reading and writing RFID tags are closely related but fundamentally different operations. Reading retrieves identifiers that link to rich data stored in software. Writing programs those identifiers or stores limited data directly on the tag.
Understanding RFID tag memory banks, rewrite capabilities, and encoding best practices allows you to design systems that are reliable, scalable, and easier to maintain. With a clear grasp of the RFID read write process, teams can avoid common pitfalls and get more value from their RFID investments.
Before deploying at scale, it is always worth testing encoding workflows in controlled conditions and validating assumptions about tag memory, locking behavior, and software logic.
A Practical Note from the Field
For teams building or refining RFID systems, having access to a broad selection of RFID tags, readers, and encoding tools can simplify testing and deployment. Atlas RFID supports a wide range of RFID hardware and offers professional services that help organizations design encoding workflows, select appropriate tag memory options, and validate performance before rollout. Exploring these resources can be a helpful next step when moving from concept to production.
