The EM4233 is the elder of the vicinity-type NFC chips from the Swiss manufacturer EM Microelectronic (a Swatch Group company): designed for long-term asset management (libraries, archives and collections, access control, long-life tagging, supply chains), it laid down the architecture that the EM4237 family modernizes today. Compliant with the ISO/IEC 15693 and ISO 18000-3 standards, it comes in two versions: the secure EM4233, whose protection adjusts across three levels (mutual authentication with a 96-bit key, a 32-bit password, or plain-text memory), and the library-dedicated EM4233SLIC. Both offer 60 years of data retention and remain readable and writable by the vast majority of recent NFC smartphones.
Information
| Manufacturer | EM Microelectronic |
| Family | EM4233 |
| Versions | EM4233 and EM4233SLIC |
| Standard | ISO/IEC 15693 and ISO 18000-3 (vicinity cards) |
| NFC Forum type | Type 5 Tag compatible |
| Operating frequency | 13.56 MHz |
| Data rate | Up to 26 kbit/s (ISO 15693 high data rate) |
| Unique identifier (UID) | 8 bytes (64 bits), factory programmed |
| Tuning capacitance | 23.5 pF or 97 pF depending on the version |
| Operating distance | Long range with a dedicated RFID reader; a few centimeters with a smartphone |
| Data retention | 60 years |
| User memory | 208 bytes (EM4233) or 128 bytes (EM4233SLIC) |
The versions of the family
The EM4233 family comes in two versions, which share the protocol, the EAS and the longevity:
| Version | User memory | Highlights |
|---|---|---|
| EM4233 | 208 bytes (52 blocks of 32 bits) | Three-level security: 96-bit key, 32-bit password or plain-text memory |
| EM4233SLIC | 128 bytes (1 Kbit) | The library version: 32-bit password, EAS and AFI |
Used as a Type 5 NFC tag, the EM4233 hosts a URL of around 200 characters and the SLIC around 110 characters. The EM4237 family is its direct heir, with the same philosophy and modernized features.
Memory
The memory of the EM4233 chips is addressed as 4-byte blocks, with the secure EM4233 reserving part of its 2-Kbit EEPROM for configuration:
| Area | Content | Access |
|---|---|---|
| User memory | 208 or 128 bytes in 32-bit blocks | Read and/or write protections per block or per page; permanent locks |
| Configuration area | 12 reserved blocks on the EM4233 (security, parameters) | Managed through dedicated commands, according to the chosen security level |
| Registers and identity | 8-byte UID, AFI and DSFID registers | UID set at the factory; registers writable then lockable |
The EM4233 thus reserves 12 of its 64 blocks for configuration and security, hence its 208 usable bytes. Access protections are lifted in secure mode (through the key or the password, depending on the configuration), with only the permanent locks remaining irreversible.
Features & security
- Three-level security (EM4233): the same chip can be configured for true mutual authentication (a fast crypto engine, a true random generator and a 96-bit secret key), for 32-bit password protection through the login command, or as a simple plain-text memory: the level adjusts to the application's exact needs, up to advanced anti-theft protection.
- Per-block and per-page protections: reading and/or writing can be protected separately, block by block or page by page, and permanent locking remains possible; in secure mode, the protections yield to the holder of the key or password.
- Flexible EAS and AFI: the smart, configurable anti-theft feature, combined with the application family identifier, makes the family compliant with worldwide library standards and infrastructures.
- Destroy function: protected by a password, it deactivates the label permanently and irreversibly.
- Quiet Storage: this feature speeds up mass inventories by durably keeping already-counted tags out of the dialogue, an asset for well-stocked shelves.
- Proven longevity: with 60 years of retention (archives and long-life books are explicitly targeted), two tuning capacitances (23.5 and 97 pF) and a -40 to +85 °C range, the family is built to last.
The EM4233 laid down the architecture (secure mode through login, per-page protections, EAS, destroy) that the EM4237 family carries over and modernizes. Worth noting: EM only releases the full EM4233 datasheet under a non-disclosure agreement, with its public fact sheet summarizing the essentials.
Compatibility
The EM4233 chips use NFC-V technology (ISO/IEC 15693), supported by the vast majority of recent NFC smartphones. On Android, reading and writing work natively with NFC Tools, without any particular restriction. On iPhone, automatic background reading is available from the iPhone XS and XR onwards; models from the iPhone 7 can read and write these chips via NFC Tools on iOS 15.6 or later, by starting the scan manually from the app.
With NFC Tools, the EM4233 chips support reading technical information, writing records, erasing and locking. The password, the EAS and the destroy function are managed through the chip's dedicated commands, and the 96-bit key authentication of the EM4233 requires specialized infrastructures. The list of compatible models is available in the article on compatibility.
EM4233 vs EM4237
| Chip | User memory | Security | Positioning |
|---|---|---|---|
| EM4233 / EM4233SLIC | 208 or 128 bytes | 96-bit key or password, EAS, destroy | The founding generation, installed fleets |
| EM4237SLIC / SLIX | 128 or 256 bytes | 32-bit password, customizable EAS, privacy, Random ID, destroy | The current successor |
From one generation to the next, the architecture remains (secure mode through login, per-page protections, EAS, destroy): the EM4237 adds the Random ID, the privacy mode and the customizable EAS telegram, with its secure version replacing the proprietary 96-bit key engine with standardized Grain-128A cryptography. For a new project, the EM4237 family is the way to go; on the NXP and STMicroelectronics side, the ICODE SLIX and ST25TV cover the same ground.
Frequently asked questions
How much data can be stored on an EM4233?
The EM4233 offers 208 usable bytes (52 of its 64 32-bit blocks, the rest being reserved for configuration), i.e. a URL of around 200 characters; the EM4233SLIC offers 128 bytes, around 110 characters.
What are the three security levels of the EM4233 worth?
They cover the whole spectrum: mutual authentication with a 96-bit secret key (with a crypto engine and a true random generator) for advanced anti-theft protection, the 32-bit password through login for everyday use, or plain-text memory when simplicity comes first. The level is chosen according to the application, on the same chip.
Are the EM4233 chips compatible with iPhones?
Yes. Background reading works from the iPhone XS and XR onwards, and both reading and writing are possible via NFC Tools from the iPhone 7 on iOS 15.6 or later.
Can an EM4233 chip be protected against rewriting?
Yes: per-block or per-page write protections are reversible in secure mode (through the key or the password), permanent block-by-block locking is irreversible, and the destroy function can deactivate the label entirely at the end of its life.
Useful links
