Abstract

There are over 30 different 1-Wire^® devices, including iButton^® devices, that Maxim currently produces. Navigating the available APIs, software examples, and other resources to communicate with this array of devices or finding the correct resource for a single device type can be a daunting task. This document provides an overview of the available resources and a selection guide. The current 1-Wire devices are also presented in a convenient table, providing device descriptions and family code lookup.

Available APIs include TMEX (an API for Microsoft Windows^®), 1-Wire Public Domain Kit (a cross-platform API), the 1-Wire API for Java^™ (OWAPI) and its variant 1-Wire API for .NET (OW.NET), and 1-Wire API for .NET Compact (OW.NET.Compact). All of the APIs described in this document are free to use without restriction and, in most cases, include the complete source code.

Introduction

There are over 30 different 1-Wire devices, including iButton devices, that Maxim currently produces. Navigating the available application program interfaces (APIs), software examples, and other resources to communicate with this array of devices, or finding the correct resource for a single device type, can be a daunting task. This guide provides an overview of available resources and a selection guide. The APIs described in this document are free to use without restriction and, in most cases, include the complete source code.

1-Wire Overview

The 1-Wire bus is a simple signaling scheme that performs two-way communications between a single master and peripheral devices over a single connection. A powerful feature that all 1-Wire bus devices share is that each and every device, in a chip or an iButton, has a factory-programmed registration number that will never be repeated in any other device. In effect, every device is unique. This allows any single device to be individually selected from among the many that can be connected to the same bus wire. Because one, two, or even dozens of 1-Wire devices can share a single wire for communications, a binary searching algorithm is used to find each device in turn. Once each device registration number is known, any device can be uniquely selected for communication using that registration number to address it.

The first part of any communication involves the bus master issuing a reset, which synchronizes the entire bus. A slave device is then selected for subsequent communications. This can be done by selecting all slaves, selecting a specific slave (using the registration number of the device), or by discovering the next slave on the bus using a binary search algorithm. These commands are referred to collectively as network function or read-only-memory (ROM) commands. Once a specific device has been selected, all other devices drop out and ignore subsequent communications until the next reset is issued.

Once a device is isolated for bus communication, the master can issue device-specific commands to it, send data to it, or read data from it. Because each device type performs different functions and serves a different purpose, each type has a unique protocol once it has been selected. Even though each device type may have different protocols and features, they all have the same selection process and follow the command flow seen in Figure 1.

An integral part of the unique registration number in each slave is an 8-bit family code. This code is specific to the device model. Because each device model performs different functions, this code is used to select the protocol that will be used to control or interrogate it. See Table 1 for a mapping of family codes for Maxim 1-Wire parts.

*This list may not include all Maxim 1-Wire device types (families), just the ones directly supported by the Automatic Information Business Unit's (BU's) software libraries.

¹These devices are no longer recommended for new designs.

API Fundamentals

The different APIs for communicating with 1-Wire devices have common features that reflect the fundamental communication issues arising from the protocol. Figure 2 outlines the common groupings of the functions for the different APIs. Since most 1-Wire devices have memory, the memory I/O functions are treated as a common API group although the functions do not apply to all devices. All other nonmemory specialty functions are lumped into the device-specific device grouping.

The typical sequence to use these functions is outlined in Figure 3. The SESSION functions wrap around the communication calls to the device, which typically involve using a NETWORK function followed by a memory or DEVICE-specific operation.

The nature of iButton communication is inherently 'touch.' This means that contact with the device is not always reliable. The iButton might be inserted into the reader and have intermittent contact during the read. Consequently a consistent methodology of error recovery must be rigorously followed. This usually entails doing retries when a spurious error is detected and utilizing CRC checks in data communication. The file I/O functions in the APIs use a standard file structure detailed in the 1-Wire File Structure section of application note 114, "1-Wire File Structure." This structure uses a CRC16 on every page of data to quickly verify the validity of the data being read. Most of the 1-Wire API functions have little or no automatic retries. The retries are under application control. See the application note 159, "Software Methods to Achieve Robust 1-Wire^® Communication in iButton^® Applications," for methodology of error recovery and risk assessment in doing 1-Wire communication.

API Selection

There are principally five different APIs that are considered in this document. The APIs operate on different platforms, use different languages, and have different capabilities. Table 2 displays these five APIs with a brief description, and Table 3 maps the operating system with the available APIs divided by language.

*MxTNI^™ is an embedded platform with a Java-based OS made by Maxim.

¹No longer supported. Legacy driver downloads still available from the Maxim web site.

The support of the individual device families also varies from API to API. Table 4 lists all of the currently available 1-Wire devices with flags indicating the available support in each API. The key for the Table 4 flags is located at the bottom. Note that the device cells without shading are considered fully supported by the API. A light-shaded cell indicates partial support, and dark-shaded cell indicates minimal support.

¹These devices are no longer recommended for new designs.

1-Wire Public Domain (PD) Overview

The functions provided in 1-Wire PD API are completely written in 'C' and are intended to be used on platforms not supported by the TMEX API. The '1-Wire net' (or MicroLAN^™) is a single wire and ground network with one master and one or more slave devices. This API creates a 1-Wire master that can be used to identify and communicate with slave devices. It provides all of the 1-Wire, transport, and file level services to communicate with all of the 1-Wire devices, including iButtons. This API kit and sample platform builds are available on the iButton web site.

The 'C' source code to this API is designed to be portable. There are provided 'TODO' templates to be completed for a specific platform. Several platform example implementations are provided including: Windows 64-bit, Windows 32-bit, and Linux. There are also several example applications that use these platform implementations.

There are three sets of portable source files defined as 'general,' 'userial,' and 'other.' The first set is general purpose and is intended for platforms that already have the primitive link 1-Wire communication functions (general). This is the lowest level that is hardware dependent. The second set of portable source files assumes that the user has a serial port (RS-232) and wishes to utilize the 'Universal Serial 1-Wire Line Driver Master: DS2480B' (userial). This chip receives commands over the serial port, performs 1-Wire operations, and then sends the results back to the serial port. The source code converts the intended 1-Wire operations into serial communications packets to the DS2480B. The only module that need be provided for a platform are the serial port read/write primitives. The DS2480B is the interface chip used in all of the DS9097U series serial adapters. Finally, the third set of portable source files deal with specific 1-Wire adapter functionality and/or does not quite fall into the previous categories (other). An example of this deals with the USB port, specifically utilizing the DS2490 USB to 1-Wire bridge chip. In many ways, this is similar to the general build, but has been modified for DS2490 specificity. No matter which file set is used (general, userial, or other), in the end, the same API is actually published to the software developer.

In particular, this application note also presents the open-source, cross-platform libusb build of the 1-Wire Public Domain Kit (classified as an 'other' build). Libusb is an open-source USB library that has been ported across many different OSs. This particular build(s) of the 1-Wire PD API compiles in the necessary libusb functions that are used to then construct the 1-Wire PD API.

See table below for the various file sets available, which have already been built for each platform presented in the table and are available for download.

Note: Refer to the 1-Wire Public Domain Kit web site for latest platform builds.
¹The DS1410E parallel port adapter is not recommended for new designs.

These sets of portable source code files implement the same 1-Wire API functions and are interchangeable. Figure 4 shows the available API for version 3.xx of the 1-Wire PD code base. Note that the nonmemory-device-specific functions are not listed in detail due to their large number. Figure 4 maps the source files that provide the functions and the required modules for new platforms.

In addition to the portable 'C' modules in the PD kit download, there are also a limited number of microprocessor (µP) assembly examples to perform 1-Wire communication.

The file functions in this API implement the 1-Wire File Structure type 'AA' defined by application note 114, "1-Wire File Structure."

As the name of this API would imply, the source code provided has a license that is as close to being public domain as possible. Developers are free to use and integrate this code into their applications without restriction.

Example 1 shows a PD code fragment that follows the API usage flow outlined in Figure 3. For simplicity, each device on the 1-Wire network is discovered during each pass through the work loop. A more sophisticated application could potentially find just one device type or perhaps select a device found in a previous search.

int rslt, portnum=0, doing_work=1;
char portString[50]; // set to platform appropriate port string

// work loop 
while (doing_work)
{
  // acquire the 1-Wire Net (SESSION)
  if (owAcquire(portnum, portString))
  {
   // find all devices (NETWORK)
   rslt = owFirst(portnum, TRUE, FALSE);
   while (rslt)
   {
     // do SOMETHING with device found (TRANSPORT/FILE/DEVICE)
     // . . .

     // find the next device (NETWORK)
     rslt = owNext(portnum, TRUE, FALSE);
   }

   // release the 1-Wire Net (SESSION)
   owRelease(portnum);
  }
  else
  {
   // Could not acquire 1-Wire network 
   // . . . 
  }

  // do other application work 
  // . . .
}

Figures 5a and 5b list the C-language modules that make up each of the two sets of 1-Wire PD libraries. Also displayed are the 'TODO' functions that must be provided to port the library to a new platform. Several example platform link files that implement the 'TODO' functions are provided in the kit.

SESSION
owsesu.c
LINK
owllu.cds2480ut.cds2480.h
NETWORK
ownetu.ccrcutil.c (required to compile)
TRANSPORT
mbappreg.c	mbappreg.h	mbee.c	mbee.h	mbee77.c	mbee77.h
mbeewp.c	mbeewp.h	mbeprom.c	mbeprom.h	mbnv.c	mbnv.h
mbnvcrc.c	mbnvcrc.h	mbscr.c	mbscr.h	mbscrcrc.c	mbscrcrc.h
mbscree.c	mbscree.h	mbscrex.c	mbscrex.h	mbscrx77.c	mbscrx77.h
mbsha.c	mbsha.h	mbshaee.c	mbshaee.h	owtrnu.c	pw77.c
pw77.h	rawmem.c	rawmem.h
FILE
owcache.c	owfile.c	owfile.h	owpgrw.c	owprgm.c
DEVICE
ad26.c	ad26.h	atod20.c	atod26.c	atod26.h	cnt1d.c
humutil.c	humutil.h	jib96.c	jib96.h	jib96o.c	ps02.c
ps02.h	sha18.c	sha33.c	shadbtvm.c	shadebit.c	shaib.c
shaib.h	swt05.c	swt12.c	swt12.h	swt1c.c	swt1c.h
swt1f.c	swt29.c	swt29.h	swt3a.c	swt3a.h	temp10.c
thermo21.c	hermo21.h	time04.c	time04.h	weather.c	weather.h
MISC UTILITY
ioutil.c	owerr.c	findtype.c	ownet.h	screenio.c	sprintf.c
crcutil.c
TODO
Provided a SERIAL interface module that implements the following functions: BreakCOM* - Sends a 'BREAK' on the serial port for at least 2ms. CloseCOM - Closes the previously opened serial port. (optional for some platforms) FlushCOM* - Allows any pending write operations to complete and clear input buffer. msDelay* - Delays at least the specified number of milliseconds. msGettick - Returns an increment millisecond counter. (optional for some examples) OpenCOM - Opens the specified serial port for communication. (optional for some platforms) ReadCOM* - Reads a specified number of bytes from the serial port. SetCOMBaud - Changes the serial BAUD rate to the rate specified. (optional if needs overdrive) WriteCOM* - Writes a specified number of bytes to the serial port. * Minimum functions required for basic operation.

Installation

The 1-Wire PD API is a set of C modules, so there is no formal installation. As provided in the example builds, the required modules are compiled directly into the applications. This does not preclude developers from combining the modules into a loadable library such as a Windows DLL.

Keep in mind that some builds require native 1-Wire adapter drivers or equivalent. As most OS platforms have built-in serial port drivers, the userial builds of the 1-Wire PD API do not need any other driver. However, for USB and parallel port 1-Wire adapter support, native or cross-platform drivers will need to be installed. References to the appropriate driver downloads are available in the documentation of the actual 1-Wire PD Kit builds available online.

1-Wire API for Java (OWAPI) Overview

The 1-Wire API for Java was designed from the ground up to be a very robust, highly object-oriented foundation for building 1-Wire applications in Java. It extends the ability of programmers to develop portable, cross-platform software and shortens the time to market for their 1-Wire integrated products.

The API consists of many Java classes and interfaces. One special group of Java classes in the 1-Wire API is the container (class OneWireContainer). Support for particular 1-Wire devices, including iButtons, is provided through containers. The API has over 30 different container types, representing most 1-Wire devices. Each container encapsulates and implements the functionality of an individual device.

A container interacts with a 1-Wire device through a 1-Wire adapter class that represents a physical 1-Wire adapter (class DSPortAdapter). The instance of the adapter is produced from the provider class (class OneWireAccessProvider). The actual implementations of the 1-Wire adapters vary from platform to platform, but they all have the same interface. Some platforms use native drivers, but most at least support the DS9097U-XXX serial adapters using RXTX (a cross-platform serial COM port API). This API is available from RXTX's GitHub page.

The 1-Wire API for Java Software Development Kit is available on the iButton web site. Like the 1-Wire PD Kit, the complete Java source to OWAPI is provided under a public-domain-style license.

Figure 6 shows the typical object creation sequence for this API. The 'provider' creates an instance (or enumeration) of an 'adapter,' which in turn can create instances of device 'containers.' Communication to the device is then performed almost exclusively through the container.

Figure 7 shows the common features of a container. A device that contains memory will create a memory bank instance for each memory bank. The memory is divided up into banks depending on the feature set of the bank. For example, one bank could be volatile while another is nonvolatile. Or, a bank could be general-purpose memory or it could be memory-mapped to change the functionality of the device.

Figure 8 shows the methods provided by the base OWAPI classes. The class or package is displayed in bold. Note that, because each container has high level methods to manipulate each device type, the LINK level methods in the adapter are not usually called directly.

Example 2 shows a OWAPI code fragment that follows the API usage flow outlined in Figure 3. Like the PD code example in Example 1, each device on the 1-Wire network is discovered during each pass through the work loop, while a more sophisticated application could find just one device type or a previously found device.

boolean doing_work=true;

// get the default adapter from the service provider
DSPortAdapter adapter = OneWireAccessProvider.getDefaultAdapter();

// work loop
while (doing_work)
{
  // get exclusive use of adapter (SESSION)
  adapter.beginExclusive(true);

  // clear any previous search restrictions (NETWORK)
  adapter.setSearchAllDevices();
  adapter.targetAllFamilies();
  adapter.setSpeed(adapter.SPEED_REGULAR);

  // enumerate through all the 1-Wire devices found (NETWORK)
  for (Enumeration owd_enum = adapter.getAllDeviceContainers();
    owd_enum.hasMoreElements(); )
  {
   // get a 'container' for each device 
   OneWireContainer owd = ( OneWireContainer ) owd_enum.nextElement();

   // do SOMETHING with device found (TRANSPORT/FILE/DEVICE)
   // . . . 
  }

  // end exclusive use of adapter (SESSION)
  adapter.endExclusive();

  // do other application work 
  // . . .
}

1-Wire Tagging

As 1-Wire sensors get more numerous and diverse, it becomes increasingly difficult to manage a 1-Wire network. For example, a sensor like an ADC could measure various different values, so it becomes important to be able to tag the sensor to describe its function. A 1-Wire tagging scheme using XML has been created and implemented in the 1-Wire API for Java. These tags allow an application to dynamically load and configure a sensor to give it a context. Please refer to application note 158, "1-Wire Tagging with XML," for details.

Installation

All of the required modules that make up the API calls described in Figure 8 are contained in a single jar file: OneWireAPI.jar. Placing this one module in the correct location or classpath provides the entire API. There are two noted exceptions to this: there could be native or communication APIs required to be installed for a particular platform, or the platform could have size constraints so that it is undesirable to have the entire API available. These two exceptions are examined in detail in the OWAPI kit.

1-Wire .NET (OW.NET) Overview

For all intents and purposes, the .NET support we offer is the 1-Wire API for Java, only compiled with the Microsoft J# language. All .NET 1-Wire applications only need to reference the OneWire.NET.dll. This includes support for the latest .NET languages, such as C#, J#, and VB.NET. For 1-Wire .NET examples, please refer to the appropriate software development kit (SDK) download on the iButton web site.

Keep in mind that the OneWire.NET.dll also needs the following redistributables installed on a PC before the 1-Wire applications will work properly:

1. Native 1-Wire port adapter device drivers. These are known as 1-Wire Drivers and can be downloaded from the iButton web site.
2. Microsoft .NET 2.0 Framework
3. Visual J# .NET 2.0 Redistributable

For those desiring Compact .NET Framework 1-Wire support for devices such as Pocket PCs, personal digital assistants (PDAs), mobile phones, and set-top boxes, a new link-layer (only) version of the OneWire.NET.dll is available. It was written entirely in C#. Currently, no OneWireContainers have been written for it, but the DSPortAdapter classes are available. See the 1-Wire SDK for Windows for further details.

The OW.NET API is provided in a 1-Wire drivers package that also includes the TMEX API. For details on how to create a custom install of the 1-Wire Drivers, please see the following application note 1740, "White Paper 6: 1-Wire Drivers Installation Guide for Windows."

1-Wire .NET Compact (OW.NET Compact) Overview

The interface for this object is identical to the 1-Wire .NET (OW.NET) however only the Session, Link, and Network layers are implemented. The object does not have a formal distribution install, but is instead a single DLL (OneWireLinkLayer.dll). This object communicates directly with the TMEX API on both 32- and 64-bit Windows platforms. The DLL file can be included with a 2.0 .NET application for low-level 1-Wire support. This object was written in C#, so it does not require the J# 2.0 .NET redistributable package.

TMEX API (TMEX) Overview

The TMEX API is a set of language-independent Windows DLLs that provides basic functionality to all 1-Wire devices including limited 1-Wire File Structure support to memory devices. The API is designed to work in multiprocess, multithreaded applications all vying for the same or different 1-Wire ports. The API can support up to 16 different types of 1-Wire adapters each with 16 distinct ports. It supports all 1-Wire adapters created by Maxim.

The lowest level of this API (the lowest level device-driver layer) is used as the native drivers for the 1-Wire API for Java on Windows platforms (1-Wire Drivers). Since the 1-Wire .NET API is also based on the 1-Wire API for Java, it is also used there. Figure 9 shows graphically how the other APIs take advantage of the native support that the TMEX API provides. Included in this figure are the actual driver file names and how they are layered.

Both available on the Maxim web site are the 1-Wire Drivers installation package (containing the TMEX API and OW.NET libraries) and the Software Developer's Kit containing many example programs linked to TMEX (and accompanying APIs).

All of the examples provided in the TMEX SDK are provided with source code. However, the source code for the low-level drivers is currently not provided, though the drivers can be redistributed without restriction.

Table 6 lists the currently supported 1-Wire adapters along with the features of each adapter.

¹These adapters are no longer recommended for new designs.

Windows Platforms Supported by TMEX

The following Microsoft Windows platforms are supported by TMEX: Windows 2008, Windows 2003, Windows Vista, and Windows XP SP2. This includes both x86 (32-bit) and x64 (64-bit) operating system versions. Please note that if drivers for earlier Windows operating system versions are required, legacy versions of TMEX are available, though not actively supported, from Maxim's web site. Please download version 4.00 or below of the 1-Wire Drivers (which install the TMEX API libraries). 1-Wire Drivers installation packages can be found here: iButton: 1-Wire Drivers for Windows.

Figure 10 lists functions provided by the TMEX API. Note that this API does not provide any nonmemory-device-specific functions.

Example 4 shows a TMEX code fragment that follows the API usage flow outlined in Figure 3. Like the last three examples, a simple process allows each device on the 1-Wire network to be discovered during each pass through the work loop while other, more sophisticated applications can find just one device type or select from those devices previously found.

int PortNum, PortType; // port number and type set for adapter present
long session_handle; // session handle
unsigned char state_buffer[5120];
int doing_work=1, did_setup=0;
short rslt;

// work loop 
while (doing_work)
{
  // aquire the 1-Wire Net (SESSION)
  session_handle = TMExtendedStartSession(PortNum,PortType,NULL);
  if (session_handle > 0)
  {
   // check to see if TMSetup has been done once
   if (!did_setup)
   {
     if (TMSetup(session_handle) == 1)
      did_setup = 1;
     else
     {
      // error setting up port, adapter may not be present
      // . . . 
     }
   }
   else
   {
     // find all devices (NETWORK)
     rslt = TMFirst(session_handle, state_buf);
     while (rslt > 0)
     {
      // do SOMETHING with device found (TRANSPORT/FILE/DEVICE)
      // . . .

      // find the next device (NETWORK)
      rslt = TMNext(session_handle, state_buf);
     }
   }

   // release the 1-Wire Net (SESSION)
   TMEndSession(session_handle);
  }
  else
  {
   // Could not acquire 1-Wire network 
   // . . . 
  }
  
  // do other application work 
  // . . .
}

Installation

The TMEX API gets installed with the previously mentioned 1-Wire Drivers installation package (which also installs OW.NET API libraries). It is a Microsoft installer package that loads all of the Windows drivers and registry keys for every supported 1-Wire adapter. The driver and API files (no install) are also freely available online for custom installations. The OneWireViewer is a demonstration program that exercises most 1-Wire and iButton devices and is installed with the 1-Wire drivers.

More information on the 1-Wire Drivers and OneWireViewer demo can be found on the iButton web site under "Software Resources."

Other Tools

While the APIs discussed in this document represent a large part of the available resources for communication with 1-Wire devices, it is by no means the only resource. This section outlines some other available resources.

Software Authorization API

Software authorization is simply the locking of a software application to require the presence of a hardware token. The token in this case is an iButton connected to the user's workstation. The application polls for the presence and validity of the iButton before running. It can also continuously query while the application executes. In practice, any of the APIs outlined in this document can be used for this type of application; however, there are specific concerns that must be considered. External drivers present a weakness to the security by allowing a user to replace the driver and thereby defeat the lock. The software authorization API, built upon the 1-Wire PD Kit, has been developed specifically for this type of application and includes linkable modules instead of external drivers.

The design of the Software Authorization API is centered on the simplest use cases possible, to make integration into the software programmer's existing code easy. There are three main services provided by the API:

• Initializing a 1-Wire device
• Authenticating the device
• Clearing a device (so it is no longer a valid part of the system)

Information on the 1-Wire Software Authorization Kit can be found on the iButton web site.

Software Example Search Engine

Maxim continually develops 1-Wire example software applications demonstrating the APIs described in this document. Examples that do not appear in the SDKs can be found by utilizing our online Software Example Search Engine. Many of these examples (with source code) are added to the search engine first (as a separate download) before being added to its respective SDK. The search engine can search for software examples by:

• 1-Wire device (Thermochron, SHA iButton, etc.)
• Platform (Win32, Linux, MxTNI, etc.)
• API (TMEX, 1-Wire Public Domain, 1-Wire .NET, etc.)
• Programming language (C, Java, C#, Visual Basic, Delphi, etc.)

Included in the search results are a description of the program and its appropriate download link.

Third Party

A large volume of third-party software is available for 1-Wire devices. Some are applications produced by Maxim authorized solutions developers (ASDs) for purchase with their solution. A complete list of ASDs and a solution locator are provided on the iButton site, as well as open-source projects on public forums like SourceForge.net.

Conclusion

This document provides an overview of the characteristics of any 1-Wire API. It also details several different APIs, including supported platforms and programming languages. A quick-reference table providing each API's coverage of each device type helps facilitate selection of which API to use. With the correct API in hand, an application utilizing 1-Wire can readily be designed.