Touch Memory & iButton FAQ
Straight answers to the questions buyers and installers actually ask about iButton, DS1990A, TM keys, rewritable blanks, readers, compatibility, lifetime and ordering.
What is the difference between DS1990A and TM1990A?
Functionally there is none that a reader can detect. Both present a unique, read-only 64-bit ROM over the 1-Wire bus and answer the same commands, so they are interchangeable in the same installation. DS1990A is the original Dallas/Maxim part number; TM1990A is the widely produced equivalent used for volume issuance at a lower cost per unit.
Can an RW1990 be rewritten, and how many times?
Yes. The RW1990 is a writable emulator: its 64-bit ID can be programmed and re-programmed with any standard TM duplicator, typically on the order of 100,000 write cycles. That is what allows a key-cutting shop to copy an existing DS1990A onto a fresh blank in seconds.
Will a TM1990A work in a reader designed for DS1990A?
Yes. Any reader that speaks the 1-Wire ROM protocol will read a TM1990A exactly as it reads a DS1990A. Physical fit is identical too — both use the F5 can, 16.25 mm across the flange.
What is a family code and how do I identify a key from its number?
The 64-bit ROM is structured as an 8-bit family code, a 48-bit unique serial number and an 8-bit CRC. The family code identifies the device type: 01h is a DS1990A serial-number key, 0Ch is a DS1996 64 Kb memory device, 21h is a DS1921 Thermochron, and so on. Read the family code and you know what you are holding.
Magnetic or non-magnetic Dallas key — which do I need?
It depends on the reader. Magnetic keys carry a steel ring so the key seats and stays on the contact — the "touch and hold" behaviour many intercom panels rely on. Non-magnetic keys cost less and suit readers that do not need retention. If you are re-keying an existing site, match whatever the installed readers already use.
How is Touch Memory different from RFID such as EM-Marine or Mifare?
Touch Memory is a contact technology: the key must physically touch the reader, which draws power and data over a single wire. RFID is contactless and works at a distance. The practical consequences: contact keys are cheaper, immune to remote relay attacks, and unaffected by radio interference, but they wear mechanically and are slower in high-throughput lanes.
Can one universal blank replace Cyfral and Metakom keys?
Yes — that is what the TM08v2 universal blank is for: it emulates Dallas Touch Memory as well as the Cyfral and Metakom formats, so a shop can stock one blank instead of three. Where the estate requires copies that cannot be re-copied, use the OTP blanks instead: TM-01A for Dallas and RW2000 for Cyfral/Metakom — they program once, then lock. Coverage still depends on the duplicator, so test with your own equipment before committing to volume.
What is the expected lifetime and operating temperature?
The stainless can is rated for roughly −40 °C to +85 °C and is sealed against moisture and dust, which is why these keys survive outdoor entrance panels. Read-only keys have no battery and no practical electrical wear limit; in the field the failure mode is almost always mechanical — a lost key or a worn contact surface, not a dead chip.
What is your MOQ, lead time and customization capability?
We ship popular SKUs from stock and run OEM batches on short cycles. We can supply custom ROM ranges, housing colours, laser marking, your logo and private-label packaging. Tell us the model and annual volume and we will send current pricing and free samples.
Dallas, Maxim and iButton are trademarks of their respective owners. We manufacture compatible products and are not affiliated with them.