![]() When idle, a high-impedance path between the 1-Wire bus and the operating voltage puts the 1-Wire bus in the logic-high state. The timing logic of master and slave must measure and generate digital pulses of various widths. The 1-Wire concept relies both on a master that initiates digital communication, and on self-timed 1-Wire slave devices that synchronize to the master's signal. A 1-Wire system consists of a single 1-Wire master and one or more 1-Wire slaves. The 1-Wire Interface General Informationġ-Wire is the only voltage-based digital system that works with two contacts, data and ground, for half-duplex bidirectional communication. Temperature logger iButtons ® use SRAM technology and, therefore, do not have any special, external power requirements. Besides EEPROM devices, the strong pullup also powers 1-Wire temperature sensors and special functions such as a SHA-1 engine, which is found in secure 1-Wire devices. The extra power is needed for write cycles and, in case of the DS1977, also for reading. To ensure proper power, EEPROM devices may need a master that supports "strong pullup", a feature that temporarily bypasses the 1-Wire pullup resistor with a low-impedance path. EEPROM technology is found in DS197x, DS243x and DS28Exx series devices. The next leap forward was EEPROM technology, which allows programming and erasing at 5V or less. These EPROM devices need a 12V programming pulse and are not erasable. Next the nonvolatile EPROM technology became available, and the DS198x and DS250x series devices were released. The first 1-Wire devices, the DS199x series, were produced in SRAM technology. The Technological Evolution of 1-Wire Devices Instead of merging the specifics of all relevant information into a single document, this new document refers the reader to other application notes whenever possible. (See application note 1796, " Overview of 1-Wire ® Technology and Its Use.") These various developments made it necessary to update the earlier documentation. Meanwhile, the number of 1-Wire devices also grew to a long list. Since that time special driver chips have been developed for direct connection to a UART, I☬ bus, or USB port. ![]() IntroductionĪ 1994 application note explained that the only serial-port interface options for 1-Wire devices were microcontroller port pins, UARTs, and UART-based COM ports. The 1-Wire Master Concepts section provides references to other documents that discuss 1-Wire masters in detail and to the related software. ![]() A special section explains how to determine appropriate timing parameters for a network comprised of both old and new 1-Wire slaves. This application note presents the electrical aspect of the 1-Wire protocol for new and legacy devices.
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