Solution

When working on RFID projects, many people only focus on "how large the capacity and how far the distance", but they overlook ahidden but fatal parameter - block size.

In the 13.56MHz high-frequency band, you'll see tags labeled with 4 bytes/block , 8 bytes/block , and 16 bytes/block for MIFARE Classic . This isn't something the manufacturer arbitrarily sets; it directly determines your read/write speed, data layout, production line cycle time, and even after-sales rework rate .

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I. What exactly is block size: The "smallest writing grid" for high-frequency tags

The EEPROM of high-frequency RFID (ISO/IEC 15693, ISO 14443A, etc.) is not written arbitrarily in "bytes," but is divided into blocks.

• The reader issues commands: Read Single Block / Write Single Block 

• Each operationmust be performed as a whole block. 

• Number of bytes within a block = Block size (commonly 4 / 8 / 16 / 32 bytes) 

Analogy: A block is like a grid in a notebook; you must fill a whole grid when you write, you can't just fill half a grid

• Typical ISO 15693 chips (ICODE SLI, TI HF-I, LRI2K):4 bytes/block or8 bytes/block 

• MIFARE Classic 1K/4K (14443A):16 bytes/block, with 4 blocks forming a sector 

• Some Fujitsu/ST high-capacity HF chips: support 8 bytes or 32 bytes/block 

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2. Why are some 4 bytes and some 8 bytes?

It's not about "who is more advanced," but ratherthe difference in protocol requirements and chip positioning.

block size	Typical Representative	Original Design Intent
4 bytes	ICODE SLI, Ultralight	Low cost, small data, supply chain conflict prevention
8 bytes	Some HF-I Plus and Fujitsu 2K	Balancing UID and small load, reducing the number of blocks
16 bytes	MIFARE Classic	Card-based applications with key/value block operations
32 bytes	Large capacity 15693	Fewer tubes, more space, improved throughput

The ISO 15693 standard itselfdoes not mandate block size, but only specifies that "block length can be configured, with a maximum of 256 blocks".

Therefore, even with the same high-frequency tag, changing the chip will change the block size

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III. Four Real-World Impacts of Block Size on Applications (Principle Level)

1️Read/write count ≠ data volume ÷ bytes, but rather ÷ blocks 

Suppose you want to write 32 bytes of user data:

• 4 bytes/block → 8 writes 

• 8 bytes/block → 4 writes 

• 16 bytes/block → Write twice 

Each block write operation includes: a command frame + tag EEPROM programming time (a few milliseconds to tens of milliseconds) + CRC response

The smaller the block, the more times the same amount of data is returned, and the more easily the production line cycle time is disrupted

2️Data alignment: Misaligned block boundaries = read/write failure 

A common error message in industrial PLCs is: "Write length not multiple of block size"

because:

• Writing a 5-byte tag to a 4-byte/block tag → must be padded to 8 bytes (2 blocks) 

• The card reader addresses by "block address" and rejects the card if the blocks are misaligned 

Many instances of "intermittent read failures" are actually caused bythe host computer trying to read 4-byte block tags using a 16-byte approach.

3️Conflict prevention and group reading efficiency

ISO 15693 supports multiple labels in the same field

Smaller blocks mean faster single-tag counting, butslower overall data retrieval.

Large blocks mean fewer single-tag interactions, making them suitable for "tray-level" output of tens of bytes at a time

4️The Hidden Costs of Lifespan

• 4-byte block: Simple control logic, small wafer area → Cheaper tags 

• Large blocks + FRAM: Fast write speed and long erase/write life (10^12 vs EEPROM 10^5), but higher unit price 

Choosing the wrong block size will eitherwaste moneyor preventthe production line from accelerating.

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IV. A Golden Rule for High-Frequency Selection

Storing only the UID/batch number is sufficient in a 4-byte block, saving costs

To store process parameters/counts/station records → select 8 bytes or more, or simply use the FRAM large user area

Integration with the MIFARE access control system → Accepting 16-byte block displays

The reader must recognize this block size; otherwise, even the best tags will be useless.

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V. Why should we pay more attention to the " WELLAUTO (WELLAUTO)" high-frequency label in industrial settings? 

Having explained the principles, let's get down to practical application—a regular white card can run a demo, butmachine tools, CNC machines, painting lines, and brake light assembly, the size of the block is just the basics; survival is the key.

Several key features of WELLAUTO AU3 series high-frequency RFID tags:

•13.56MHz Full Protocol Compatibility: Supports ISO 15693 / 14443A / NFC, with the block structure exposed as is on the chip itself, without hidden encapsulation, and easy alignment on the PLC side. 

•Anti-metal performance is the real deal: The AU3 IHT-TM series uses ferrite magnetic shielding and coil topology optimization, achievinga stable reading distance of up to 220mm when mounted on stainless steel/aluminum parts, without relying on "foam padding" to cheat. 

•Flexible block size matching for chips: From 1024-bit EEPROM to 8K-byte FRAM, it can accommodate 4/8/16-byte block sizes, and can be used without disrupting existing production lines during migration. 

Industrial-grade packaging: PPS + epoxy/brass nickel plating, IP67–IP68, -40~100℃ normal operation,some models can withstand 220℃ short-term baking(direct placement on the coating line).

•Compact Fitting: Φ12 / Φ16 / M12 threaded models can be inserted into tool holders, mold positioning holes, and brake light semi-assemblies without affecting the mechanical structure. 

•Bus-level connectivity: Equipped with AU3 IHR reader/writer, native ProfiNet/EtherCAT/IO-Link, RFID data is directly mapped to the PLC I/O area without writing middleware. 

•Verified through traceability scenarios: Batch testing has been conducted on automotive SCR components, brake light assembly lines, and CNC tool management systems; these are not just parameters on paper. 

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VI. Ending in one sentence

The size of the grid is the "writing grid" of high-frequency RFID. 4 bytes saves costs, 8 bytes achieve a balance, and 16 bytes are more suitable for card applications. The choice of grid determines how many more parts your production line can process per second

But when the environment becomes metal, oil, high temperature, and vibration—no matter how beautiful the grid is drawn, it's useless if the label can't survive

This is why more and more smart manufacturing projects are replacing high-frequency labels from "Taobao white cards" with the WELLAUTO  AU3 IHT series : transparent block structure, powerful industrial packaging, and worry-free bus integration.

If you are working on tool management/tooling traceability/automotive parts assembly lines, I can calculate a landing table for you based on yourreader/writer model + data field length, including "block alignment + tag model + read/write cycle time".