DS1985: iButton 16Kb Add-Only Data Sheet (Rev. 4)9/16/2009690K
Features and Benefits
- 16384 bits Electrically Programmable Read Only Memory (EPROM) communicates with the economy of one signal plus ground
- EPROM partitioned into sixty-four 256-bit pages for randomly accessing packetized data records
- Each memory page can be permanently write-protected to prevent tampering
- Device is an "add only" memory where additional data can be programmed into EPROM without disturbing existing data
- Architecture allows software to patch data by superseding an old page in favor of a newly programmed page
- Reduces control, address, data, power, and programming signals to a single data pin
- 8-bit family code specifies DS1985 communications requirements to reader
- Reads over a wide voltage range of 2.8V to 6.0V from -40°C to +85°C; programs at 11.5V to 12.0V from -40°C to +85°C
The iButton® 16Kb add-only (DS1985) is a rugged read/write data carrier that identifies and stores relevant information about the product or person to which it is attached. This information can be accessed with minimal hardware, for example a single port pin of a microcontroller. The DS1985 consists of a factory-lasered registration number that includes a unique 48-bit serial number, an 8-bit CRC, and an 8-bit Family Code (0BH) plus 16Kb of EPROM which is user-programmable. The power to program and read the DS1985 is derived entirely from the 1-Wire communication line. Data is transferred serially via the 1-Wire protocol which requires only a single data lead and a ground return. The entire device can be programmed and then write-protected if desired. Alternatively, the part may be programmed multiple times with new data being appended to, but not overwriting, existing data with each subsequent programming of the device. Note: Individual bits can be changed only from a logical 1 to a logical 0, never from a logical 0 to a logical 1. A provision is also included for indicating that a certain page or pages of data are no longer valid and have been replaced with new or updated data that is now residing at an alternate page address. This page address redirection allows software to patch data and enhance the flexibility of the device as a standalone database. The 48-bit serial number that is factory-lasered into each DS1985 provides a guaranteed unique identity which allows for absolute traceability. The durable MicroCan package is highly resistant to harsh environments such as dirt, moisture, and shock. Its compact button-shaped profile is self-aligning with cup-shaped receptacles, allowing the DS1985 to be used easily by human operators or automatic equipment. Accessories permit the DS1985 to be mounted on printed circuit boards, plastic key fobs, photo-ID badges, ID bracelets, and many other objects. Applications include work-in-progress tracking, electronic travelers, access control, storage of calibration constants, and debit tokens.
Product Lifecycle Production
At least one model within this product family is in production and available for purchase. The product is appropriate for new designs but newer alternatives may exist.
Documentation & Resources
1-Wire Search Algorithm3/28/2002
Reading and Writing 1-Wire® Devices Through Serial Interfaces3/29/2001
Advanced 1-Wire Network Driver2/14/2023
iButton Data Loggers5/17/2019
Protecting 5V 1-Wire® Slaves from Overvoltage Exposure5/30/2011
OneWireViewer and iButton Quick Start Guide3/11/2009
White Paper 2: Using the 1-Wire® Public Domain Kit7/16/2008
1-Wire Software Resource Guide Device Description7/8/2008
Overview of 1-Wire Technology and Its Use6/19/2008
Software Methods to Achieve Robust 1-Wire® Communication in iButton® Applications9/11/2007
What Is an iButton Device?5/17/2006
White Paper 5: Using 1-Wire APIs for Data Sheet Commands6/7/2002
1-Wire Communication Through Software5/30/2002
Using the DS2480B Serial 1-Wire® Line Driver3/12/2002
Add-Only Memory for Secure Storage of Monetary Equivalent Data3/8/2002
Programming 1-Wire EPROM and EEPROM Memory Devices Using a PC1/2/2002
1-Wire File Structure7/11/2001
Understanding and Using Cyclic Redundancy Checks with Maxim 1-Wire and iButton Products3/29/2001
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