The ST25TB family gathers the Type B contactless memories from STMicroelectronics, heirs of the SR chips that made ticketing history: transport tickets, ski passes, event ticketing, loyalty and consumables. Built on the lower layers of the ISO/IEC 14443B standard with a proprietary protocol (no NDEF, outside the tag types standardized by the NFC Forum), its four references offer 512 bits to 4 Kbits of EEPROM, two 32-bit decrement-only counters and a resettable OTP area: the toolkit of the reloadable, tamper-proof ticket. Their compatibility with smartphones is limited, however, and detailed below.
Information
| Manufacturer | STMicroelectronics |
| Family | ST25TB |
| References | ST25TB512-AC, ST25TB512-AT, ST25TB02K and ST25TB04K |
| Standard | ISO/IEC 14443B (levels 2 and 3, proprietary protocol) |
| NFC Forum type | None (no NDEF message) |
| Operating frequency | 13.56 MHz |
| Data rate | 106 kbit/s |
| Unique identifier (UID) | 8 bytes (64 bits), factory programmed |
| Tuning capacitance | 68 pF |
| Operating distance | A few centimeters (up to 10 cm depending on the antenna) |
| Data retention | 40 years |
| Write endurance | 1,000,000 cycles |
| Memory | From 512 bits to 4 Kbits (64 to 512 bytes) depending on the reference |
The references of the family
The ST25TB family comes in four references, which share the same protocol, the same counters and the same command set:
| Reference | Memory | Highlights |
|---|---|---|
| ST25TB512-AC | 64 bytes | Resettable OTP area and two 32-bit counters |
| ST25TB512-AT | 64 bytes | Transport-dedicated version, available as a thinned wafer |
| ST25TB02K | 256 bytes | Extended memory, same structure and counters |
| ST25TB04K | 512 bytes | The largest capacity of the family |
The memory is addressed as 32-bit blocks (16 blocks on the 512 versions, 64 on the 02K, 128 on the 04K), read and written randomly through a set of nine commands: a deliberate simplicity that makes the ST25TB an economical solution for reusable products issued in very large volumes.
Memory
The memory of the ST25TB chips is organized into three areas with distinct behaviors, tailored for ticketing:
| Area | Content | Behavior |
|---|---|---|
| Resettable OTP area (blocks 0 to 4) | 160 bits that can only switch from 1 to 0 | Global reset to 1 through a dedicated command; blocks permanently lockable |
| Counters (blocks 5 and 6) | Two 32-bit binary counters | Decrement only, by steps of 1 or more; can never be reloaded |
| EEPROM memory (following blocks) | 32-bit blocks, freely rewritable | Automatic erase at each block write |
This organization tells the story of a ticket: the OTP bits tick off consumed rights (and reset as one block when the ticket is reloaded), the counters count down trips or points with no way back (more than four billion events each), and the EEPROM holds the holder's data. No NDEF message lives there: reading is performed by the system's readers, not by the general public.
Features & security
- Two tamper-proof counters: the 32-bit counters can only decrement, by steps of 1 or more, and can never be reloaded; an anti-tearing mechanism guarantees their consistency even if the card leaves the field mid-operation: the foundation of a fraud-proof ticket count.
- Resettable OTP area: the 160 bits of the first five blocks only switch from 1 to 0 (the consumption of a right), with a dedicated command resetting them all to 1 during a system-controlled reload.
- Permanent locking: each block of the OTP area can be locked individually and irreversibly, to freeze issuance data.
- Anticollision and simplicity: the anticollision mechanism selects each tag present in the field, and the reduced set of nine commands (32-bit block reads and writes at 106 kbit/s) keeps costs at their lowest for very large volumes.
- The SR legacy: the family carries over the architecture of STMicroelectronics' SR memories, proven for years in transport networks, ski resorts and ticketing, with a single 68 pF antenna tuning.
The transport-dedicated ST25TB512-AT version is offered as a thinned wafer (75 µm) for the thinnest tickets. Data retention reaches 40 years for one million write cycles.
Compatibility
The ST25TB family relies on a proprietary protocol built on the lower layers of ISO/IEC 14443B, outside the tag types standardized by the NFC Forum: it contains no NDEF message, and its compatibility with smartphones is therefore limited. On Android, the chip is detected (NFC-B technology) and NFC Tools can read its technical information, such as the UID. On iPhone, this family is not supported, as iOS does not handle this proprietary protocol: neither background reading nor manual reading is available.
Writing the blocks, managing the counters and locking require a dedicated RFID reader or encoder, through the chip's own commands. For a tag meant to be read by smartphones, the ST25TA (NFC-A) or ST25TV (NFC-V) families are the way to go. The list of compatible models is available in the article on compatibility.
ST25TB vs ST25TA
| Family | Standard | Strengths | Positioning |
|---|---|---|---|
| ST25TB | ISO/IEC 14443B (proprietary, no NDEF) | Tamper-proof counters, OTP area, low cost | Ticketing and closed systems |
| ST25TA | ISO/IEC 14443A (NFC Forum Type 4) | NDEF file, 128-bit passwords, TruST25 | Smartphone interaction and consumer use |
The two families do not play in the same league: the ST25TB equips closed systems where only the operator's readers talk to the tags, while the ST25TA targets direct interaction with smartphones. On the NXP side, the MIFARE Ultralight EV1 covers the ticketing segment in NFC-A technology; for a universal consumer tag, the NTAG213 remains the reference.
Frequently asked questions
Which ST25TB reference should I choose?
The ST25TB512-AC covers common tickets and loyalty cards; the ST25TB512-AT, available as a thinned wafer, targets the thinnest transport tickets; the ST25TB02K and 04K offer 256 and 512 bytes when the holder's data or the history grows.
What are the two 32-bit counters for?
Counting down rights with no way back: remaining trips, entries, points. Each counter can only decrement (by steps of 1 or more), can never be reloaded and benefits from an anti-tearing mechanism: more than four billion events, fraud-proof.
Are the ST25TB chips compatible with iPhones?
No. Their proprietary protocol, outside the NFC Forum types, is not supported by iOS: neither background reading nor manual reading. On Android, detection and reading of technical information remain possible with NFC Tools; full operation goes through dedicated RFID readers.
Can an ST25TB chip be protected against rewriting?
By nature, the counters never go back up and the OTP bits only switch from 1 to 0 (resetting them to 1 requires a dedicated command); the first five blocks can also be locked individually and permanently. The rest of the EEPROM remains freely rewritable.
Useful links
