DS1994 4 Kbit NV RAM + RTC iButton
Memory plus a clock, interval timer, cycle counter and alarms in one token.
The most capable memory iButton: 512 bytes of battery-backed NV RAM combined with a real-time clock (1/256-second resolution), an interval timer that accumulates power-on time, a cycle counter that counts power on/off events, and programmable alarms with 1-Wire interrupts on all three. Write-protect bits make the time data tamper-proof, and a write-protected counter can expire access — turning the token read-only after a set time or usage. Ideal for time-limited and usage-limited access, metering and audit trails. Shares its die with the DS2404 chip.
The only token that can expire by itself
Memory and a clock together change what a key can do. Because the DS1994 has a real-time clock, an interval timer that accumulates powered-on time and a cycle counter — all with programmable alarms and all protectable by write-protect bits — access rights can live inside the token instead of inside the controller. Issue a contractor a key that stops working next Friday, or after 200 uses, and no central database has to be updated when it does. Nothing else in this range can do that: the DS1904L has the clock but no memory, the DS1993 has the memory but no clock.
Key features
- Combines 512 bytes of NV RAM with a real-time clock, interval timer, cycle counter and alarms.
- RTC at 1/256-second resolution, ±2 min/month; interval timer accumulates power-on time; cycle counter counts on/off events.
- Programmable alarms on all three counters generate 1-Wire interrupts; write-protect bits make time data tamper-proof.
- A write-protected counter can expire access — turning the token read-only after a set time or usage.
- Family code 04h; over 10 years retention; UL 913 rated; shares its die with the DS2404 chip.
Specifications
| Chip / compatibility | DS1994 · family code 04h · chip-form DS2404 |
|---|---|
| Memory | 4 Kbit NV RAM (16 pages × 256 bits) + RTC + interval timer + cycle counter + alarms |
| Protocol | 1-Wire, 16.3 kbit/s; RTC 1/256 s resolution, ±2 min/month at +25 °C |
| Package | F5 can |
| Operating temperature | −40 to +70 °C; over 10 years data retention; UL 913 rated |
Inside the stainless can
A 0.25 mm solid stainless shell, a UV-stable polypropylene grommet isolating lid from base, and the die bonded inside. Lid = data contact, base = ground return.
Which memory iButton do you need?
The whole memory range side by side, grouped by storage technology — capacities and family codes per the Analog Devices datasheets.
| Model | Family code | Capacity | Memory technology | Pick it for |
|---|---|---|---|---|
| DS1971 | 14h | 256 bit + 64-bit OTP | EEPROM — battery-free | Asset tag: a locked ID beside rewritable data |
| DS1972 | 2Dh | 1 Kbit (128 B) | EEPROM — battery-free | Per-page write-protect or EPROM-emulation modes |
| DS1973 | 23h | 4 Kbit (512 B) | EEPROM — battery-free | Largest battery-free memory; production travellers |
| DS1982 | 09h | 1 Kbit (128 B) | EPROM — add-only, cannot be erased | Tamper-evident checkpoints and certificates |
| DS1985 | 0Bh | 16 Kbit (2 KB) | EPROM — add-only, cannot be erased | Full append-only service history |
| DS1992 / DS1993 | 08h / 06h | 1 Kbit / 4 Kbit | NV RAM — battery-backed, unlimited writes | Data that changes constantly on the key |
| DS1996 | 0Ch | 64 Kbit (8 KB) | NV RAM — battery-backed, unlimited writes | Portable database — the largest capacity here |
| DS1994 | 04h | 4 Kbit + RTC | NV RAM + clock, timer, counter, alarms | Time- or usage-limited access that expires by itself |
| DS1904L | 24h | No user memory | Real-time clock only | Give a microcontroller an accurate timebase |
| DS1991 | 02h | 1152 bit = 3 × 384 bit | Secure NV RAM — three password zones | Legacy multi-tenant systems (not for new secure designs) |
| DS1961S | 33h | 1 Kbit + 64-bit secret | EEPROM + SHA-1 challenge–response | The anti-cloning choice — proves it knows a secret |
Ordering information
| MOQ | 100 pcs |
|---|---|
| Lead time | 3–7 days for stock items, 10–15 days for OEM |
| Packing | Bulk ESD bags (100–200 pcs/bag, 2 bags/carton); blister or header cards for retail on request |
| Samples | Free samples for volume buyers — courier at cost |
| Payment | T/T bank transfer; other terms negotiable for repeat orders |
| Shipping | DHL / FedEx / UPS air express; sea or rail freight for pallet volumes |
| Customization | ROM ranges · housing colours · laser logo · private label |
Typical applications
Frequently asked questions
How does a DS1994 make a key expire on its own?
It carries its own real-time clock, an interval timer that accumulates powered-on time and a cycle counter, each with a programmable alarm. Because those registers can be write-protected, a controller can read the token's own clock or counter and refuse access once a date or usage limit is passed — the entitlement travels inside the key instead of a central database, which is why it suits contractors, rentals and metered service.
Related products
DS1991 MultiKey iButton
Three password-protected 384-bit subkeys in one button.
DS1992 / DS1993 Memory iButton
1 Kb and 4 Kb NV RAM tokens for carrying data on the key.
DS1996 64 Kb Memory iButton
The large-memory token — 64 Kb of rewritable NV RAM.
DS1961S SHA-1 Authentication iButton
1 Kb EEPROM with on-chip SHA-1 challenge–response.