The EM4237 family gathers the vicinity-type NFC chips from the Swiss manufacturer EM Microelectronic (a Swatch Group company), tailored for long-term asset management: libraries, access control, industrial laundries, ticketing, casinos and supply chains. Compliant with the ISO/IEC 15693 and ISO 18000-3 standards, its SLIC and SLIX versions offer 128 or 256 bytes of password-protectable memory, a smart EAS with a customizable telegram, privacy and Random ID modes and a destroy function; the secure EM4237 version adds full cryptography (Grain-128A, encrypted channel, ECC certificate). All of them can be read and written by the vast majority of recent NFC smartphones.
Information
| Manufacturer | EM Microelectronic |
| Family | EM4237 |
| Versions | EM4237SLIC, EM4237SLIX and EM4237 (secure version) |
| 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 53 kbit/s (fast multiple read) |
| Unique identifier (UID) | 8 bytes (64 bits), factory programmed; optional Random ID |
| Tuning capacitance | 23.5 pF |
| Operating distance | Long range with a dedicated RFID reader; a few centimeters with a smartphone |
| Data retention | 60 years |
| Write endurance | 100,000 cycles |
| User memory | 128 or 256 bytes depending on the version |
The versions of the family
The EM4237 family comes in three versions, which share the ISO/IEC 15693 protocol and the same longevity:
| Version | User memory | Highlights |
|---|---|---|
| EM4237SLIC | 128 bytes (1 Kbit) | 32-bit password, smart EAS, privacy, Random ID, destroy |
| EM4237SLIX | 256 bytes (2 Kbits) | Identical to the SLIC, doubled memory |
| EM4237 (secure) | 256 bytes (2 Kbits) | Grain-128A cryptography: mutual authentication, encrypted channel, ECC certificate |
The SLIC and SLIX names answer NXP's ICODE SLIX directly, on the shared ground of libraries and asset management. Used as a Type 5 NFC tag, the SLIC hosts a URL of around 110 characters and the SLIX around 240 characters.
Memory
The memory of the EM4237SLIC and SLIX is addressed as 4-byte blocks, grouped into pages of 4 blocks (16 bytes) which carry the protections:
| Area | Content | Access |
|---|---|---|
| User memory | 128 or 256 bytes, in 4-byte blocks grouped into pages | Per-page protections (four modes); permanent block-by-block locking |
| Blocks 24 to 31 | The EAS telegram, customizable through simple writing | Configurable length from 32 to 256 bits |
| Configuration area | UID, password, registers (AFI, DSFID, EAS, privacy, destroy) | Not directly accessible; managed by commands in secure mode |
Each page can be free, write-protected, read-protected (the chip then returns zeros) or both; the secure mode, opened by the Login command and the 32-bit password, lifts these protections and gives access to the configuration. On delivery, the memory is blank and fully accessible, and the password is set to zero.
Features & security
- Secure mode and per-page protections: a 32-bit password (changeable with the Change Key command) opens the secure mode; each 16-byte page can forbid reading, writing or both, with a read-protected page hiding its content behind zeros, while permanent locking remains possible block by block.
- Smart EAS for libraries: the anti-theft feature returns a telegram of 32 to 256 bits whose content is freely customizable (it consists of user blocks 24 to 31), with a 16-bit identifier allowing selective alarm; its state can be locked and password protected.
- Privacy and Random ID: the privacy mode silences the chip to any command except entering the secure mode; the Random ID regenerates part of the identifier at each power-up, with the real UID only revealed in secure mode, to protect the holder's privacy.
- Destroy function: protected by the password, it deactivates the chip permanently and irreversibly, at the end of the product's life.
- Secure EM4237 version: the cryptographic sibling relies on the Grain-128A algorithm with three-pass mutual authentication, optional encryption of the entire radio channel (Secure Messaging, a claimed first in ISO 15693), a message authentication code (MAC) and a 32-byte ECC certificate attesting the authenticity of the silicon.
- Swiss craftsmanship and longevity: designed by EM Microelectronic-Marin (Swatch Group), the family targets long-term asset management with 60-year retention, a 2.2 × 1.78 mm package and a wafer thinned to 152 µm for ticketing.
On delivery, the EAS is deactivated, the privacy and Random ID modes are inactive and all access is free. Writing a block takes around 5 ms.
Compatibility
The EM4237 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 EM4237 chips support reading technical information, writing records, erasing and locking. The password, the EAS and the privacy and destroy modes are managed through the chip's dedicated commands, and the cryptographic features of the secure version require specialized readers and infrastructures. The list of compatible models is available in the article on compatibility.
EM4237 vs ICODE SLIX
| Chip | User memory | Security | Positioning |
|---|---|---|---|
| EM4237SLIC / SLIX | 128 or 256 bytes | 32-bit password, customizable EAS, privacy, destroy | Libraries and asset management |
| ICODE SLIX (NXP) | 112 bytes | Privacy password, EAS, AFI | The installed reference for libraries |
Both play on the same ISO 15693 ground of libraries and inventory: the EM4237 stands out with its more generous memory, its per-page protections and its customizable EAS telegram, the ICODE with its huge installed base. On the STMicroelectronics side, the ST25TV family covers the same segment; for a consumer NFC tag using NFC-A technology, the NTAG213 remains the reference.
Frequently asked questions
Which EM4237 version should I choose?
The SLIC (128 bytes) covers everyday labeling and libraries; the SLIX (256 bytes) takes over when the data grows; the secure version is the way to go as soon as the application requires cryptographic authentication or an encrypted radio channel.
What makes the EAS of the EM4237 "smart"?
Its anti-theft telegram is not fixed: its length can be configured from 32 to 256 bits and its content customized by simply writing blocks 24 to 31, with a 16-bit identifier allowing selective alarm. The whole feature can be locked and password protected, a level of flexibility designed for library systems.
Are the EM4237 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 EM4237 chip be protected against rewriting?
Yes, on two levels: per-page write protection, reversible through the 32-bit password, and permanent block-by-block locking, which is irreversible. The destroy function can furthermore deactivate the chip entirely at the end of its life.
Useful links
