The ICODE SLI is NXP Semiconductors' historic NFC chip for large-scale object identification: libraries, logistics, supply chain, baggage. The first generation of the ICODE family (reference SL2 ICS20), it relies on the ISO/IEC 15693 standard (known as vicinity) which allows long-range reading and the simultaneous inventory of many tags. Compatible with the NFC Forum Type 5 format, it can be read and written by the vast majority of recent NFC smartphones.
Information
| Manufacturer | NXP Semiconductors |
| Family | ICODE (first SLI generation) |
| Reference | SL2 ICS20 |
| Standard | ISO/IEC 15693 (vicinity cards) |
| NFC Forum type | Type 5 Tag compatible |
| Operating frequency | 13.56 MHz |
| Data rate | Up to 53 kbit/s |
| Unique identifier (UID) | 8 bytes (64 bits), factory programmed |
| Operating distance | Up to 1.5 m with a long-range reader; a few centimeters with a smartphone |
| Data retention | 10 years |
| Write endurance | 100,000 cycles |
| Total memory (EEPROM) | 128 bytes (1,024 bits) |
| User memory | 112 bytes |
Memory
The EEPROM memory of the ICODE SLI is organized into 32 blocks of 4 bytes, including 28 user blocks; only blocks 0 to 27 can be addressed with the read and write commands:
| Area | Content | Access |
|---|---|---|
| System blocks (4 blocks) | 64-bit UID, write access conditions (locks), AFI and DSFID | Read-only UID; one-way lock bits; AFI and DSFID writable and lockable |
| Blocks 0 to 27 | User memory (112 bytes) | Read / write, lockable block by block |
In practice, the 112 bytes of user memory can hold an NDEF record containing a URL of around 95 characters, once the Capability Container (written into the first block during formatting) and the NDEF envelope are taken into account, with the common prefix (https://www. for example) compressed into a single byte: encoding a short redirect link is recommended. The EAS, AFI and DSFID identifiers reside in the system area, outside the addressable space.
Features & security
- Multi-tag inventory: the ISO/IEC 15693 anticollision, complemented by the inventory read and fast inventory read commands, makes it possible to census many tags simultaneously present in the field, an entire library shelf or box for example.
- EAS (Electronic Article Surveillance): a built-in anti-theft feature, detectable at a gate with a dedicated command, which can be enabled, disabled and locked.
- AFI (Application Family Identifier): an application family identifier filters the inventory by object type, to sort mixed logistics flows.
- Block-by-block locking: each 4-byte block can be write-protected irreversibly, through one-way lock bits; the DSFID, AFI and EAS can also be locked. The operation can be performed directly from NFC Tools.
- Symmetrical range: the write distance is equal to the read distance, an asset for encoding tags on the fly on a logistics line.
The ICODE SLI does not offer password protection: that feature appears with the ICODE SLIX, its backward-compatible replacement. The first generation also came as the ICODE SLI-S and SLI-L, with different capacities and features.
Compatibility
The ICODE SLI uses 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 the chip via NFC Tools on iOS 15.6 or later, by starting the scan manually from the app.
With NFC Tools, the ICODE SLI chip supports reading technical information, writing records, erasing and permanent locking. The list of compatible models is available in the article on compatibility.
ICODE SLI vs ICODE SLIX
| Chip | User memory | Security | Typical use |
|---|---|---|---|
| ICODE SLI | 112 bytes | EAS and AFI without password | First generation, existing systems |
| ICODE SLIX | 112 bytes | EAS and AFI protectable by password | The backward-compatible replacement |
Both chips share the same memory and the same protocol. The backward-compatible ICODE SLIX replaces the SLI for new deployments; the following generations, ICODE SLIX2 and ICODE DNA, further extend memory and security.
Frequently asked questions
How much data can be stored on an ICODE SLI?
The chip has 112 bytes of user memory, which corresponds to a URL of around 95 characters once the Capability Container and the NDEF envelope are taken into account. Encoding a short redirect link is recommended.
What is the difference between ICODE and NTAG?
NTAG chips rely on the ISO/IEC 14443 proximity standard, limited to a few centimeters, while ICODE chips use ISO/IEC 15693, known as vicinity: the range exceeds one meter with a suitable reader and dozens of tags can be inventoried simultaneously. ICODE chips thus dominate libraries and logistics, NTAG chips consumer tags.
Is the ICODE SLI 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 ICODE SLI be protected against rewriting?
A permanent, irreversible lock is possible block by block, including from NFC Tools. However, the chip does not offer password protection: that feature was introduced with the ICODE SLIX.
Useful links
