DS1985 16 Kbit Add-Only EPROM iButton
16 Kbit add-only EPROM for append-only records that should not be altered.
2 KB of add-only EPROM in sixty-four 256-bit pages: per the original manufacturer's datasheet, data can be programmed but not erased, and each page can be permanently write-protected (confirm for the supplied version). Software can supersede an old page with a newly programmed one, giving append-only ledger behaviour. A candidate for stored-value tokens and audit trails that should not be altered. Shares its die with the DS2505 chip.
Ordering information
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An append-only ledger with room to grow
The DS1982 keeps a handful of events that cannot be edited; the DS1985 does the same across sixty-four pages and 2 KB. That is the difference between a checkpoint stamp and a complete service history — every intervention on a machine, every calibration, every custody transfer, appended in order and, by the part's design, not erasable. Software supersedes an old page by programming a newer one, so the ledger reads forward in time while the original entries stay exactly where they were written.
Key features
- Original DS1985 reference: 16 Kbit add-only EPROM arranged as 64 pages of 256 bits.
- Original pages support permanent write protection and redirection; EPROM bits can be programmed from 1 to 0.
- Confirm the host’s record layout and dedicated programming requirements; use application-level verification for stored-value systems.
Specifications
| Chip / compatibility | DS1985 · family code 0Bh · chip-form DS2505 |
|---|---|
| Memory | 16 Kbit add-only EPROM (64 pages × 256 bits) |
| Protocol | 1-Wire, 16.3 kbit/s; reads at 2.8–6.0 V, programs at 12 V — per the original manufacturer's datasheet; confirm for the supplied version |
| Package | F3 / F5 can |
| Operating temperature | −40 °C … +85 °C (1-Wire chip, per the original manufacturer's datasheet; confirm for the supplied version) |
Inside the stainless can
Typical construction of this can format: a stainless-steel shell, an insulating grommet separating lid from base, and the chip bonded inside. Lid = data contact, base = ground return. Wall thickness, grommet material and other construction details: confirm for the supplied version.
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 | Battery-free rewritable memory (4 Kbit); production travellers |
| DS1982 | 09h | 1 Kbit (128 B) | EPROM — add-only; written data is not erasable (per datasheet) | Add-only records such as checkpoints and certificates |
| DS1985 | 0Bh | 16 Kbit (2 KB) | EPROM — add-only; written data is not erasable (per datasheet) | Append-only service history (16 Kbit) |
| DS1992 / DS1993 | 08h / 06h | 1 Kbit / 4 Kbit | NV RAM — battery-backed, high write endurance (per datasheet) | Data that changes constantly on the key |
| DS1996 | 0Ch | 64 Kbit (8 KB) | NV RAM — battery-backed, high write endurance (per datasheet) | Portable database — 64 Kbit NV RAM |
| DS1994 | 04h | 4 Kbit + RTC | NV RAM + clock, timer, counter, alarms | Time- or usage-limited access with the expiry held in the key |
| DS1904L | 24h | No user memory | Real-time clock only | Give a microcontroller a real-time 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 | Authentication: proves it knows a secret (assess cloning risk for your own system) |
Typical applications
Frequently asked questions
How is the DS1985 related to the DS1982?
Per the original manufacturer's datasheets, the same add-only EPROM concept with sixteen times the space: 16 Kbit in sixty-four 256-bit pages. Data can be programmed but not erased, and each page can be write-protected; confirm for the supplied version.
What is append-only memory good for?
Typical candidates are records that may later need to be shown as evidence: stored-value tokens, maintenance and service histories, audit trails. Software supersedes an old page by programming a new one, so the ledger grows rather than being rewritten.
What voltages does it need?
Per the original manufacturer's datasheet, it reads parasite-powered at 2.8–6.0 V over 1-Wire, while programming requires a 12 V pulse, which makes casual tampering in the field less likely. F3 or F5 can, −40 to +85 °C; confirm for the supplied version.
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.