TUTORIALS 1796

Guide to 1-Wire Communication


Abstract: This article provides a general overview of Maxim’s 1-Wire® technology, its communication concept and the benefit of low pin count package options. The main section discusses 1-Wire devices by their feature set and explains the typical applications. The article concludes with practical information on how to evaluate 1-Wire devices, explains device customization options, and references resources that assist customers with integration of 1-Wire technology in their systems.

What Is 1-Wire Technology?

The basis of 1-Wire® technology is a serial protocol using a single data line plus ground reference for communication. A 1-Wire master initiates and controls the communication with one or more 1-Wire slave devices on the 1-Wire bus (Figure 1). Each 1-Wire slave device has a unique, unalterable, factory-programmed, 64-bit identification number (ID), which serves as device address on the 1-Wire bus. The 8-bit family code, a subset of the 64-bit ID, identifies the device type and functionality. Typically, 1-Wire slave devices operate over the following four voltage ranges:

  • 1.71V (min) to 1.89V (max)
  • 1.71V (min) to 3.63V (max)
  • 2.97V (min) to 3.63V (max)
  • 2.8V (min) to 5.25V (max)

Most 1-Wire devices have no pin for a power supply; they take their energy from the 1-Wire bus (parasitic power supply).

The 1-Wire master/slave configuration uses a single data line plus ground referenceFigure 1. The 1-Wire master/slave configuration uses a single data line plus ground reference.

What Is Special About 1-Wire?

1-Wire is a voltage-based digital system that works with two contacts, data and ground, for half- duplex bidirectional communication. Compared to other serial communication systems such as I2C or SPI, 1-Wire devices are designed for use in a momentary contact environment. Either disconnecting from the 1-Wire bus or a loss of contact puts the 1-Wire slaves into a defined reset state. When the voltage returns, the slaves wake up and signal their presence. With only one contact to protect, the built-in ESD protection of 1-Wire devices is extremely high. With two contacts, 1-Wire devices are the most economical way to add electronic functionality to nonelectronic objects for identification, authentication, and delivery of calibration data or manufacturing information.

How Are 1-Wire Devices Packaged?

1-Wire devices are offered in conventional transistor (TO-92) and IC (TSOC, TDFN, SOT23) packages. Designed for contact applications and easy attachment, the 2-contact SFN1 package accommodates parasitically powered 1-Wire devices (Figure 2). The 16mm-diameter stainless steel iButton2 package protects 1-Wire devices from harsh environments, making them suitable for indoor and outdoor use (Figure 3). Many devices are also available as bumped die (Figure 4).

The 6.0mm x 6.0mm x 0.9mm SFN package has large contact areasFigure 2. The 6.0mm x 6.0mm x 0.9mm SFN package has large contact areas.

The 16mm-diameter iButton package protects the 1-Wire chip inside from harsh environmentsFigure 3. The 16mm-diameter iButton package protects the 1-Wire chip inside from harsh environments.

A bumped die (WLP) with a 0.5mm pitchFigure 4. A bumped die (WLP) with a 0.5mm pitch.

What Device Functions Are Available, and What Are the Typical Applications?

Currently, there are a variety of 1-Wire devices. Part numbers that begin with DS19 are always in iButton packages. The remaining part numbers in this section, i.e., those that begin with DS24, DS25, and DS28, are available in conventional plastic packages. If a product is also available as an SFN, then this is mentioned in the Notes column of the following part tables. To find up-to-date package information for any device, go to the Maxim website and enter the part number in the Search field.

1-Wire devices can be grouped by their functions into several categories:

  • Identification only
  • Identification plus control
  • Identification plus temperature
  • Identification plus time
  • Identification plus NV SRAM
  • Identification plus one-time programmable (OTP) EPROM
  • Identification plus EEPROM
  • Identification plus SHA-256 authentication and secure EEPROM
  • Identification plus SHA-256/ECDSA authentication and secure memory
  • Identification plus SHA-3 authentication, ChipDNA-encrypted EEPROM
  • Identification plus data logging

The combination of additional resources determines the typical application areas for a device. There are numerous other applications that, for practical reasons, cannot be listed here.

Identification Only

Devices in this category are notable for their low cost. Accordingly, the level of protection that they can provide is limited. If the DS2401 or DS2411 is used for the protection of intellectual property (IP), one should consider a customized version of the device. See the Is There Any Device Customization Available? section for more details.

Part Number Notes Typical Applications
DS2401 The DS2401 does not need a VCC supply, thus this part is suitable for identification of printer cartridges and medical consumables.
  • Printed circuit board (PCB) identification and authentication
  • Accessory/peripheral identification
  • Protection of IP or consumer electronics
  • Printer cartridge identification
  • Access control
  • Asset management
  • DS2411 VCC power, 1.5V or higher
    DS1990A
    DS1990R
    The DS1990R is guaranteed to generate a presence pulse on contact to reader.

    Identification plus Control

    The applications for these parts are similar to the devices above. The programmable input/output pins (PIOs), however, add control or feedback capability to the system.

    Part Number Notes Typical Applications
    DS2413 Two 28V PIOs
  • Printer cartridge and medical disposable identification
  • Rack card control
  • Accessory/peripheral identification and control
  • Identification plus Temperature

    In large electronic equipment (racks), proper cooling/air flow is critical for reliable operation. The DS28EA00 solves this problem in a unique way through its chain function,3 which allows detecting the physical sequence of the device on the 1-Wire bus. When wired for sequence detection, one of the two PIOs is available for control functions.

    Part Number Notes Typical Applications
    DS28EA00 If not wired for sequence detection, two PIOs are available for control functions Rack card monitoring
    DS1920 This standalone device measures temperature on command, e.g., when a reader touches it. Temperature data collection on contact

    Identification plus Time

    These devices measure time by counting seconds using a 32-bit binary counter. Knowing the 0-time reference point (i.e., January 1, 1970, 00:00:00 hours UTC), one can identify any second within 136 years. Counting seconds is particularly convenient to measure time intervals.

    Part Number Notes Typical Applications
    DS2417 The DS2417 is also available as a wafer-level package (WLP). Periodic timer interrupt requires a 6pF, 32kHz crystal. Consumer electronics
    DS1904 This standalone iButton device includes a battery and crystal. This device is also suited for guard tour patrol systems, and time and attendance applications.

    Identification plus NV SRAM

    Data retention for the products outlined in this category is over 10 years. The size of the nonvolatile memory is shown in the Notes column.

    Part Number Notes Typical Applications
    DS1992 1Kb memory
  • PCB identification
  • Access control
  • Asset management
  • DS19934Kb memory. Due to its lower cost (compared to the DS1995/DS1996), this device is also suited for printed circuit board (PCB) identification and authentication.
  • IP protection
  • Access control
  • Asset management
  • DS199516Kb memory
    DS199664Kb memory

    Identification plus OTP EPROM

    All devices in this category use 12V EPROM technology. Since the packages do not have openings, the bits are OTP—once changed from 1 to 0, they cannot be reversed. To mark an entire 32-byte page as invalid and to point to an alternate location for valid data, these devices have redirection bytes, one for each page. This unique feature allows changing data while maintaining the change history. Individual memory pages can be irreversibly write-protected. Write protection makes OTP EPROMs prime candidates for applications that need a small amount of data that rarely changes, such as network addresses4 and PCB identification.5

    Part Number Notes Typical Applications
    DS2502 1Kb memory, available packages include WLP and SFN versions
  • Identification and usage monitoring of printer cartridges and medical consumables
  • Identification and authentication of rack cards and PCBs
  • Accessory/peripheral identification
  • DS250516Kb memory
    DS2502-E481Kb memory, preprogrammed with a MAC-48/EUI-48 Ethernet address
  • Network address
  • PCB identification
  • DS2502-E651Kb memory, preprogrammed with an IEEE® EUI-64 node address
    DS19821Kb memory
  • PCB identification
  • Asset management
  • DS198516Kb memory

    Identification plus EEPROM

    Compared to the OTP EPROMs, devices in this category do not need 12V for writing. Data can be changed (rewritten), provided that the memory area or page is not write-protected. Most of these devices have an EPROM emulation mode, which allows changing bits only from 1 to 0, as with EPROMs. Due to its high capacity and security, the DS1977 is used in the gaming industry. The DS28E80 is used extensively in the medical industry due to its gamma-radiation-resistant memory and circuits.

    Part Number Notes Typical Applications
    DS28E05 112 bytes of user memory
  • Medical consumable and PCB identification
  • Peripheral identification
  • Printer cartridge identification
  • DS28E07 1024-bit memory
  • Accessory/PCB identification
  • Aftermarket management of consumables
  • Printer cartridge identification
  • Medical sensor calibration data storage
  • DS28E80 248 bytes of user memory; gamma radiation resistant
  • Identification of medical consumables
  • Identification and calibration medical tools/accessories
  • DS2431 1Kb memory, EPROM emulation, page write protection. available packages include WLP and SFN versions
  • Identification and usage monitoring of printer cartridges and medical consumables
  • Identification of rack cards and PCBs
  • Accessory/peripheral identification
  • Protection of IP and authentication
  • Consumer electronics
  • DS28EC20 20Kb memory, EPROM emulation, block (four pages) write protection
    DS24B334Kb memory, available packages include WLP and SFN versions
  • Identification and usage monitoring of printer cartridges and medical consumables
  • Identification of rack cards and PCBs
  • Medical sensor calibration data storage
  • Accessory/peripheral identification
  • DS28E04-1004Kb memory, two 5V PIOs, seven 1-Wire address inputs, EPROM emulation, page write protection
  • Autoconfiguration of modular rack mounted systems
  • Accessory/PCB identification
  • DS1971256b memory
  • Access control
  • DS19721Kb memory, EPROM emulation, page write protection
  • Access control
  • Asset management
  • Maintenance/inspection data storage
  • DS19734Kb memory
    DS197732KB memory, password protection
  • Asset management
  • Gaming
  • Identification plus SHA-256 Authentication and Secure EEPROM

    All the devices in this secure category use a symmetric key challenge-response authentication model.6 Thus, authentication of the device and writing to the devices with proper protections activated requires knowledge of the device's secret and the ability to compute a SHA-256 MAC. Except for the secret, memory data is readable without restrictions. All the devices support challenge and response authentication, EPROM emulation for user memory pages, and various protections of the secret and memory pages. See the Is There Any Device Customization Available? section for preprogramming service.

    Part Number Notes Typical Applications
    DS28E15
    DS28EL15
    512-bit memory, bidirectional authentication; the EL part number is a low-voltage (1.671V to 1.89V) device
  • Medical consumable identification and authentication
  • Secure feature control
  • Printer cartridge identification and authentication
  • DS28E22
    DS28EL22
    2048-bit memory, bidirectional authentication, the EL part number is a low voltage (1.671V to 1.89V) device
  • Authentication of network-attached appliances
  • Key generation and exchange for cryptographic systems
  • Printer cartridge ID/authentication
  • Reference design license management
  • Secure feature setting for configurable systems
  • Sensor/accessory authentication and calibration
  • System intellectual property protection
  • DS28E25
    DS28EL25
    4096-bit memory, bidirectional authentication, the EL part number is a low voltage (1.671V to 1.89V) device
  • Identification and authentication of consumables
  • Reference design license management
  • Sensor/accessory authentication and calibration
  • System intellectual property protection
  • DS1964S512-bit memory, bidirectional authentication, iButton device
  • Access control
  • Authentication of consumables
  • Secure feature control
  • DS2465I2C interface for host communication and built-in 1-Wire master
  • SHA-256 coprocessor
  • 1-Wire master to drive SHA-256 enabled slaves on the 1-Wire bus
  • Identification plus ECDSA Authentication and Secure Memory

    All the devices in this secure category use an asymmetric key secure authentication model using the ECDSA algorithm. Some of the devices can be used for either SHA-256 or ECDSA based authentication. Authenticated or non-authenticated GPIO pins for control of external components/sensors are available on the DS28E36, DS28E83, and the DS28E84. The devices also have a decrement-only counter feature that enables the user to meter the usage of disposables. Two of the devices deploy Maxim’s ChipDNA physically unclonable function (PUF) technology to secure device data. The DS28E83/84 are high radiation resistant, thus uniquely suited for medical sterilization applications. See the Is There Any Device Customization Available? section for preprogramming service.

    Part Number Notes Typical Applications
    DS28E368Kb memory, bidirectional ECDSA or SHA-256 authentication, two GPIOs, decrement counter, on-chip random number generator (RNG), ECDH (elliptic curve Diffie-Hellman key exchange)
  • Accessory and peripheral secure authentication
  • IoT node protection
  • Secure boot or download of firmware and/or system parameters
  • Secure storage of cryptographic keys for a host controller
  • DS28E382Kb memory, unidirectional ECDSA authentication, ChipDNA, decrement counter, on-chip RNG
  • Authentication of medical sensors and tools
  • IoT node authentication
  • Peripheral authentication
  • Printer cartridge identification and authentication
  • Reference design license management
  • Secure management of limited-use consumables
  • DS28E392Kb memory, bidirectional ECDSA authentication, ChipDNA, decrement counter, on-chip RNG
  • Identification and authentication of consumables
  • Reference design license management
  • Sensor/accessory authentication and calibration
  • System intellectual property protection
  • DS28E8310Kb of OTP memory, bidirectional ECDSA or SHA-256 authentication, high radiation resistance, on-chip RNG, ECDH
  • Accessory and peripheral secure authentication
  • Medical consumables secure authentication
  • Medical tools/accessories identification and calibration
  • Secure boot or download of firmware and/or system parameters
  • Secure storage of cryptographic keys for host controllers
  • DS28E8415Kb of FRAM, 10Kb of OTP memory, bidirectional ECDSA or SHA-256 authentication, high radiation resistance, on-chip RNG, ECDH
    DS2476I2C interface for host communication; 8Kb of memory for data, keys, and certification storage
  • ECDSA and SHA-256 coprocessor to enable the host to effectively communicate with ECDSA/SHA-256 enabled 1-Wire slaves
  • Identification plus SHA-3 Authentication and Secure EEPROM

    The devices in this secure category use the SHA-3 challenge-response symmetric key secure authentication model. The devices deploy Maxim’s ChipDNA PUF technology to secure device data. It also has robust counter measures to protect against security attacks. See the Is There Any Device Customization Available? section for preprogramming service.

    Part Number Notes Typical Applications
    DS28E502Kb memory, bidirectional SHA-3 authentication, ChipDNA, decrement counter, on-chip RNG
  • Authentication of medical sensors and tools
  • IoT node authentication
  • Peripheral authentication
  • Printer cartridge identification and authentication
  • Reference design license management
  • Secure management of limited-use consumables
  • DS2477I2C interface for host communication and built-in 1-Wire master
  • SHA-3 coprocessor and 1-Wire master
  • Optimized to drive SHA-3 enabled slaves on the 1-Wire bus
  • Can be configured to be used with other 1-Wire slaves
  • DS28E16256-bit memory, unidirectional SHA-3 authentication, decrement counter, on-chip RNG, very low cost
  • Peripheral authentication
  • Printer cartridge identification and authentication
  • Secure management of limited-use consumables
  • Identification plus Data Logging

    These devices are self-contained data loggers for temperature data (Thermochron®). The DS1923 can also record humidity (Hygrochron). The principal differences among the devices are the size of the data memory and the level of data protection (password). Devices for different temperature ranges are available to meet the requirements of the various applications.7

    Part Number Notes Typical Applications
    DS1921G2KB temperature logger, -40°C to +85°C
  • Temperature monitoring for environmental science
  • Temperature monitoring for food safety
  • Quality assurance for shipments of food, produce, and pharmaceutical products
  • DS1921H2KB temperature logger, high resolution, +15°C to +46°C
    DS1921Z2KB temperature logger, high resolution, -5°C to +26°C
    DS1922E8KB temperature logger, +15°C to +140°C
    DS1922L8KB temperature logger, -40°C to +85°C
    DS1922T8KB temperature logger, 0°C to +125°C
    DS19238KB temperature and humidity logger, -20°C to +85°C
    DS1925122KB temperature logger, -40°C to +85°C

    How Does One Get Hands-On Experience with 1-Wire Products?

    If a PC with a free USB port and Internet access is available, the only items needed are: a 1-Wire adapter, evaluation (EV) software, some simple cabling, and the 1-Wire devices to evaluate. The current product prices and availability can be found on the Maxim website. The OneWireViewer software8 and related drivers can be downloaded for free.

    A more economical approach is to buy one of the EV kits. Each kit includes a 1-Wire adapter, a selection of 1-Wire or iButton devices, and the necessary cabling and accessories. Table 1 describes the EV kits available at the time of this publication. The contents of EV kits can change as new parts become available. Devices not included in a kit need to be purchased separately. The software that run the EV kits are available for free from the Maxim website or upon request depending upon the security level of the product. The package type (plastic or iButton) determines which kit best fits an application.

    Table 1. EV Kit Overview

    EV Kit Part Number Evaluates 1-Wire Adapter Type Package Contents Notes
    DS9092K#iButton devicesUSB,
    DS9490R
  • Cable with iButton probe
  • Various iButton devices
  • Mechanical iButton mounting accessories
  • DS1921K#iButton devicesUSB,
    DS9490R
  • Cable with iButton probe
  • DS1921G
  • Mechanical mounting accessories
  • DS1925EVKIT#iButton devicesUSB,
    DS9490R
  • Cable with iButton probe
  • DS1921L
  • Mechanical mounting accessories
  • Compatible with DS1922L, DS1922T, DS1922E and DS1923. (These are not included in the kit.)
    DS1964SEVKIT#DS1964SUSB,
    DS9400
  • Cable
  • DS2465 EV kit board
  • DS1402-RP8 1-Wire network cable
  • DS1964S iButton device
  • DS28EA00EVKIT#DS28EA00USB,
    DS9490R
  • Three EV boards with DS28EA00 installed
  • RJ-11 cables
  • DS28E05EVKIT#DS28E05USB,
    DS9481R-3C7
  • Cable with DS9120P+ socket board
  • DS28E05 in TSOC package
  • This kit can also be used to evaluate other 1-Wire products available in TSOC or TO-92 packages.
    DS28E80EVKIT#DS28E80USB,
    DS9481R-3C7
  • Cable with DS9120Q+ socket board
  • DS28E80 in TDFN package
  • DS28E15EVKIT#DS28E15USB,
    DS9400
  • Cable
  • DS2465 EV kit board
  • DS9120Q+ socket board
  • DS28E15 in TDFN package
  • DS28E16EVKIT#DS28E16
    DS2477
    USB,
    DS9481P-300#
  • USB cable with DS9121BQ+ socket boards
  • DS28E16 and DS2477 in TDFN packages
  • DS28E22EVKIT#DS28E22USB,
    DS9400
  • Cable
  • DS2465 EV kit board
  • DS9120Q+ socket board
  • DS28E22 in TDFN package
  • DS28E25EVKIT#DS28E25USB,
    DS9400
  • Cable
  • DS2465 EV kit board
  • DS9120Q+ socket board
  • DS28E25 in TDFN package
  • DS28E36EVKIT#DS28E36
    DS2476
    USB,
    DS9481P-300#
  • USB cable with DS9121AQ+ socket boards
  • DS28E36 and DS2476 in TDFN packages
  • DS28E38EVKIT#DS28E38
    DS2476
    USB,
    DS9481P-300#
  • USB cable with DS9121AQ+ socket boards
  • DS28E38 and DS2476 in TDFN packages
  • DS28E39EVKIT#DS28E39
    DS2476
    USB,
    DS9481P-300#
  • USB cable with DS9121AQ+ socket boards
  • DS28E39 and DS2476 in TDFN packages
  • DS28E50EVKIT#DS28E50
    DS2477
    USB,
    DS9481P-300#
  • USB cable with DS9121BQ+ socket boards
  • DS28E50 and DS2477 in TDFN packages
  • DS28E83EVKIT#DS28E83
    DS2476
    USB,
    DS9481P-300#
  • USB cable with DS9121AQ+ socket boards
  • DS28E83 and DS2476 in TDFN packages
  • DS28E84EVKIT#DS28E84
    DS2476
    USB,
    DS9481P-300#
  • USB cable with DS9121AQ+ socket boards
  • DS28E84 and DS2476 in TDFN packages
  • What Are the Next Steps to a 1-Wire Application?

    Once the 1-Wire products are selected, one needs to choose a type of master circuit (i.e., the equivalent of the 1-Wire adapter in the kits). For embedded applications, there is a multitude of choices, based on the available system resources.9 Applications that require significant cabling between the 1-Wire devices benefit from a specialized master circuit.10

    Besides hardware, firmware is needed to communicate with the 1-Wire devices, to write or read data, and to exercise control functions. A selection of software drivers 11 for various platforms is available for free download from the Maxim website. For device-specific drivers, application program interfaces (APIs), and software examples, see the 1-Wire Software Resource Guide.12 This guide also includes API functions based on the 1-Wire File Structure (OWFS),13 which are particularly useful when working with more than a few hundred bytes of data.

    Is There Any Device Customization Available?

    Maxim offers two types of device customization. Custom ROM is quite popular with identification-only devices, but it is applicable to all devices with a 64-bit ID number. With custom ROM, a pool of 68.7 × 109 numbers (equivalent to 36 bits) is committed to the sole use of a single customer. Examples of custom ROM are found in Maxim application note 178.5 This type of customization occurs before packaging, which causes a long lead-time. For SHA-256/ECDSA/SHA-3 enabled EEPROM/OTP/FRAM devices, Maxim provides a secure preprogramming service to install data and the secret. For details, submit a tech support request to the factory.

    Summary

    1-Wire technology is based on a serial communication protocol that uses a single data line plus ground reference between the master and slave. The 1-Wire slaves are available in plastic packages as bumped die or stainless-steel iButton form. The minimum function of 1-Wire slaves is a 64-bit ID number. Additional functions are PIO, temperature sensor, time counter, NV SRAM, OTP EPROM, EEPROM, SHA-256/SHA-3/ECDSA engine, SHA-256/SHA-3/ECDSA secure EEPROM, temperature logging and humidity logging. Typical applications for 1-Wire devices include identification and authentication of consumables, rack cards, PCBs, computer accessories, and the protection of IP (e.g., cloning prevention). Special uses of iButton devices are access control, asset management, guard tour systems, time and attendance, electronic cash, and temperature monitoring for food and pharmaceutical safety. Starter EV kits and software drivers are available to assist customers integrating 1-Wire technology in their systems.

    References/Other Resources

    1. Application note 4132: Attachment Methods for the Electro-Mechanical SFN Package
    2. Application note 3808: What Is an iButton Device?
    3. Application note 4037: Regain Location Information by Leveraging the 1-Wire Chain Function—A Simple Signaling and Protocol Method Determines Device Physical Location
    4. Application note 186: Creating Global Identifiers Using 1-Wire Devices
    5. Application note 178: Printed Circuit Board Identification Using 1-Wire Products
    6. Application note 3675: Protect Your R&D Investment with Secure Authentication
    7. Application note 3892: Overview of iButton Sensors and Temperature/Humidity Data Loggers
    8. Application note 3358: OneWireViewer User's Guide
    9. Application note 4206: Choosing the Right 1-Wire® Master for Embedded Applications
    10. Application note 244: Advanced 1-Wire Network Driver
    11. Start page, Software Development Kits
    12. Application note 155: 1-Wire Software Resource Guide Device Description
    13. Application note 114: 1-Wire File Structure
    Next Steps
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