Memory Block (Page)

Memory Block (Page)

A memory block (also called a page in NFC ForumNFC ForumIndustry body developing NFC standards, specifications, and certifications since 2004View full → Type 2 tags) is the smallest addressable unit of NFC tag memory. When an NFC reader issues a READ or WRITE command, it addresses data at the block level — you cannot read or write individual bytes within a block. Block size and addressing conventions vary by tag type, directly affecting how efficiently user memory can be utilized.

Block Sizes by Tag Type

Type 2 Tag Page Structure

For NTAG and MIFARE Ultralight chips, memory is organized as a linear array of 4-byte pages. A READ command returns 4 consecutive pages (16 bytes) starting from the specified page address. A WRITE command writes exactly one page (4 bytes) at a time.

The page structure has specific regions:

• Pages 0-1: Contain the 7-byte UID and manufacturer internal bytes. These pages are factory-programmed and read-only.
• Page 2: Static lock bits and internal configuration. The lock bitslock bitsControl bits making memory blocks permanently read-onlyView full → control write access to pages 3-15.
• Page 3: Capability container (CC). Describes NDEF version, memory size, and read/write access conditions.
• Pages 4 through N: User memory for storing NDEF messages and application data.
• Pages N+1 onward: Dynamic lock bits (controlling write access to the user memoryuser memoryTag memory portion available for user data storageView full → region) and chip configuration pages.

Read Alignment Considerations

Because the READ command returns 16 bytes (4 pages) regardless of how much data you need, reading a single byte still retrieves an entire 16-byte block. Similarly, writing a single byte requires reading the containing page, modifying the byte, and writing back the full 4-byte page. This read-modify-write pattern must be handled carefully to avoid corrupting adjacent data within the same page.

Block Addressing in Type 5 Tags

NFC-V / Type 5 tags based on ISO 15693 use similar 4-byte blocks but with different command sets (ReadSingleBlock, WriteSingleBlock, ReadMultipleBlocks). Some chips like the ST25DV support extended block addressing (2-byte block numbers) to address memory beyond 256 blocks (1 KB).