RFID Tag Memory Planning Guide

RFID Tag Memory Planning

A Gen 2 tag exposes four memory banks. Planning their contents before selecting an IC prevents costly re-encoding, unreadable legacy data, and security gaps. This guide covers each bank, encoding decisions, and the tradeoffs that affect IC selection.

Memory Bank Architecture

Reserved Bank: Kill and Access Passwords

The Reserved bank holds two 32-bit passwords:

• Kill password: Irrevocably silences the tag when transmitted via the RFID tag." data-category="Security">Kill command. Used in retail loss-prevention deactivation at point of sale. A zero kill password disables the kill function.
• Access password: Enables a secured session that permits lock/unlock operations and access to protected memory. A zero access password means the tag has no write protection.

Planning rule: Set non-zero passwords on all tags carrying sensitive data. Store passwords in a key management system, not in plaintext in your middleware database.

EPC Bank: Length and Encoding

EPC format." data-category="Data & Encoding">SGTIN-96 (the most common scheme) requires exactly 96 bits: 16-bit PC word + 96-bit EPC = 14 bytes total in the EPC bank. If your company prefix is longer than 30 digits or you need to encode GIAI-202 (a long asset identifier), you may need 128 or 256 bits.

The PC (Protocol Control) word in bits 0–15 of the EPC bank encodes the EPC length in 16-bit words (bits 15:11) and signals whether user memory is present (bit 10) and whether an XPC word follows (bit 9). Misconfigured PC words cause readers to misparse EPC length — a silent and hard-to-diagnose error.

Use the EPC Encoder to generate correct 96-bit hex strings with valid PC words before programming.

User Memory Planning

User memory is absent on cost-optimised ICs (e.g., base Impinj M730) and available in 32-byte (M750, UCODE 8m) or 48-byte (UCODE DNA) blocks. Plan its use:

If user memory exceeds the available bank, split data across multiple tags, use a passive tag" data-definition="Battery-assisted tag using backscatter." data-category="General">semi-passive tag with extended memory, or offload to a cloud lookup keyed on TID.

Block Write and PermaLock

Block write allows programming 2 words (32 bits) per command instead of 1, halving write time for ICs that support it. On a production line encoding 10 million tags, this difference is significant.

PermaLock is a bit-field lock that permanently locks individual 32-bit blocks in user memory. It is irreversible — once a block is permalocked, no future write can modify it. Use permalock only for immutable data (e.g., the manufacturer-assigned product code), and only after thorough quality verification.

Use the Memory Planner to lay out bank contents, calculate total byte requirements, verify PC word values, and identify ICs that meet your memory needs.

See also: Understanding EPC, How to Choose an RFID Tag, NXP UCODE Family Guide.