DS1982 Add-Only iButton
1 Kb write-once EPROM for tamper-evident records.
Physics does the enforcing here. This is EPROM without an erase path: a programmed bit stays programmed, so nothing written to a DS1982 can ever be removed or edited — not by an operator, not by a technician, not by whoever has the key in their pocket. Software can supersede an old page by programming a newer one, which gives you append-only ledger behaviour, and each of the four 256-bit pages can additionally be write-protected so it accepts nothing further at all.
Cannot be erased — that is the feature
Every rewritable device on this page can be quietly altered by whoever holds it. The DS1982 cannot, and that is why it is specified for guard-tour checkpoints, calibration certificates, warranty and maintenance logs, and any record that may one day be evidence. When an inspector asks whether the log could have been edited after the fact, "the memory has no erase function" is a stronger answer than any password. Need more room for a longer history? The DS1985 is the same idea with sixteen times the memory.
Key features
- 1 Kbit "add-only" EPROM — data can be appended but never erased, giving a tamper-evident audit trail.
- Four 256-bit pages, each permanently write-protectable; page-address redirection lets software supersede an old page.
- Reads parasite-powered at 2.8–6.0 V; programs at 12 V — the write voltage itself deters casual tampering.
- Family code 09h; unique 64-bit ROM ID; −40 to +85 °C (same die as DS2502).
- Original imported dies, canned and assembled at our own line — original-chip reliability at a sharper price; laser-etched custom marking and logos to order.
Specifications
| Chip / compatibility | DS1982 · family code 09h · shares its die with the DS2502 chip form |
|---|---|
| Memory | 1 Kbit add-only EPROM (4 pages × 256 bits) + 64-bit status memory for page write-protect bits |
| Protocol | 1-Wire · reads at 2.8–6.0 V across −40 to +85 °C; programs at 11.5–12.0 V within −40 to +50 °C · CRC-verified programming |
| Operating temperature | −40 to +85 °C · battery-free, permanent retention |
| Package | F5 can, Ø16.25 × 5.89 mm · approx. 3 g |
| Options | Laser-etched custom marking / logo on the can |
Product dimensions
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
Can data on a DS1982 really not be erased?
Correct — there is no erase mechanism in the silicon. This is EPROM in an opaque steel can with no UV window, so a programmed bit cannot be returned to its unprogrammed state by any command, password or piece of equipment. Software creates an append-only ledger by superseding an old page with a newly programmed one, and each of the four pages can also be permanently write-protected so it will accept nothing further.
What voltage does programming a DS1982 need?
Reading works at the normal 2.8–6.0 V bus level, but programming requires a 12 V pulse on the data line, so a plain read-only reader cannot write to it. Any 1-Wire adapter or programmer that supports EPROM devices provides this — check your hardware if you plan to write in the field rather than pre-programming at issue.
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.