19-4865 Rev 4/11 DS1992/DS1993 1Kb/4Kb Memory iButton SPECIAL FEATURES COMMON iButton FEATURES 4096 bits of Read/Write Nonvolatile Unique, Factory-Lasered and Tested 64-bit Memory (DS1993) Registration Number (8-bit Family Code + 1024 bits of Read/Write Nonvolatile 48-bit Serial Number + 8-bit CRC Tester) Memory (DS1992) Assures Absolute Traceability Because No 256-bit Scratchpad Ensures Integrity of Data Two Parts are Alike Transfer Multidrop Controller for MicroLAN Memory Partitioned into 256-bit Pages for Digital Identification and Information by Packetizing Data Momentary Contact Data Integrity Assured with Strict Chip-Based Data Carrier Compactly Stores Read/Write Protocols Information Operating Temperature Range from -40C to Data Can be Accessed While Affixed to +70C Object Over 10 years of data retention Economically Communicates to Bus Master with a Single Digital Signal at 16.3kbps ORDERING INFORMATION Standard 16mm Diameter and 1-Wire DS1992L-F5+ F5 MicroCan Protocol Ensure Compatibility with iButton DS1993L-F5+ F5 MicroCan Family +Denotes a lead(Pb)-free/RoHS-compliant product. Button Shape is Self-Aligning with Cup- Shaped Probes EXAMPLES OF ACCESSORIES Durable Stainless Steel Case Engraved with DS9096P Self-Stick Adhesive Pad Registration Number Withstands Harsh DS9101 Multipurpose Clip Environments DS9093RA Mounting Lock Ring Easily Affixed with Self-Stick Adhesive DS9093F Snap-In Fob Backing, Latched by its Flange, or Locked DS9092 iButton Probe with a Ring Pressed onto its Rim F5 MicroCan Presence Detector Acknowledges When Reader First Applies Voltage Meets UL 913, 5th Ed., Rev. 1997-02-24 Intrinsically Safe Apparatus, Approved under Entity Concept for use in Class I, Division 1, Group A, B, C, and D Locations 1-Wire and iButton are registered trademarks of Maxim Integrated Products, Inc. 1 of 17 DS1992/DS1993 iButton DESCRIPTION The DS1992/DS1993 memory iButtons (hereafter referred to as DS199x) are rugged read/write data carriers that act as a localized database, easily accessible with minimal hardware. The nonvolatile memory and optional timekeeping capability offer a simple solution to storing and retrieving vital information pertaining to the object to which the iButton is attached. Data is transferred serially through the 1-Wire protocol that requires only a single data lead and a ground return. The scratchpad is an additional page that acts as a buffer when writing to memory. Data is first written to the scratchpad where it can be read back. After the data has been verified, a copy scratchpad command transfers the data to memory. This process ensures data integrity when modifying the memory. A 48-bit serial number is factory lasered into each DS199x to provide a guaranteed unique identity that allows for absolute traceability. The durable MicroCan package is highly resistant to environmental hazards such as dirt, moisture, and shock. Its compact coin-shaped profile is self-aligning with mating receptacles, allowing the DS199x to be easily used by human operators. Accessories permit the DS199x to be mounted on almost any surface including plastic key fobs, photo-ID badges, and PC boards. Applications include access control, work-in-progress tracking, electronic travelers, storage of calibration constants, and debit tokens. OPERATION The DS199x have three main data components: 1) 64-bit lasered ROM, 2) 256-bit scratchpad, and 3) 1024-bit (DS1992) or 4096-bit (DS1993) SRAM. All data is read and written least significant bit first. The memory functions are not available until the ROM function protocol has been established. This protocol is described in the ROM functions flow chart (Figure 9). The master must first provide one of four ROM function commands: 1) read ROM, 2) match ROM, 3) search ROM, or 4) skip ROM. After a ROM function sequence has been successfully executed, the memory functions are accessible and the master can then provide any one of the four memory function commands (Figure 6). PARASITE POWER The block diagram (Figure 1) shows the parasite-powered circuitry. This circuitry steals power whenever the data input is high. The data line provides sufficient power as long as the specified timing and voltage requirements are met. The advantages of parasite power are two-fold: 1) by parasiting off this input, battery power is not consumed for 1-Wire ROM function commands, and 2) if the battery is exhausted for any reason, the ROM may still be read normally. The remaining circuitry of the DS1992 and DS1993 is solely operated by battery energy. 64-BIT LASERED ROM Each DS199x contain a unique ROM code that is 64 bits long. The first 8 bits are a 1-Wire family code. The next 48 bits are a unique serial number. The last 8 bits are a CRC of the first 56 bits (see Figure 2). The 1-Wire CRC is generated using a polynomial generator consisting of a shift register and XOR gates 8 5 4 as shown in Figure 3. The polynomial is X + X + X + 1. Additional information about the Maxim 1-Wire Cyclic Redundancy Check is available in the Book of DS19xx iButton Standards. The shift register bits are initialized to zero. Then starting with the least significant bit of the family code, 1 bit at a time is shifted in. After the 8th bit of the family code has been entered, then the serial number is entered. After the 48th bit of the serial number has been entered, the shift register contains the CRC value. Shifting in the 8 bits of CRC should return the shift register to all zeros. 2 of 17