The 1-Wire standard established in 1989 has been upgraded to accommodate noisy and long-line
The 1-Wire bus is a simple signaling scheme that performs two-way communication over a single electrical connection. In any
The 1-Wire scheme also enabled other applications such as chip-based tagging and long-line sensor applications. The original 1-Wire front-end did not, however, anticipate the noise levels and line characteristics (e.g., line length) of some of these new applications. Satisfying these new application demands often challenged a 1-Wire implementation in the field. Therefore, to accommodate these applications a new 1-Wire front-end called the 1-WireExtended Network Standard was developed, and incorporated into several new devices. Table 1 lists 1-Wire devices and shows which are supported by the new extended standard.
Important Features of the New Extended Standard
Noise from various sources can result in signal glitching on the 1-Wire line. The noise can come from reflections from network endpoints or branch points. (For more information, please see application note 148, "Guidelines for Reliable Long Line 1-Wire® Networks.") Noise can also come from an external source and get coupled onto the 1-Wire signal. A noise glitch during the rising edge can cause the >1-Wire device to become unsynchronized with the master. The improvements to the extended network front-end address these rising edge issues.
The new 1-Wire front-end incorporates three main components: a lowpass filter for high-frequency noise, voltage hysteresis on low-to-high switching, and a rising-edge hold-off time. Some 1-Wire devices also have slew control on the presence pulse. Figure 1 illustrates these features. The shaded pink regions show how the device ignores glitches in voltage magnitude and over a period of time during 1-Wire low-to-high transitions.
|Device||FC||Description||1-Wire Extended Network Support||Notes|
|DS1822||22||1-Wire Econo temp sensor|
|DS1825||3B||1-Wire thermometer with 4-bit address|
|DS18B20||28||Adjustable resolution temperature|
|DS18S20||10||Temperature and alarm trips|
|DS1904||24||Real-Time Clock (RTC) iButton|
|DS1920||10||Temperature and alarm trips|
|DS1921G||21||Thermochron temperature logger|
|DS1922E||41||High-Capacity Thermochron and/or Hygrochron temperature and/or humidity dataloggers, respectively||√|
|DS1961S||33||1Kb EEPROM memory with SHA-1 engine||√|
|DS1963S||18||4Kb NVRAM memory and SHA-1 engine|
|DS1971||14||256-bit EEPROM memory and 64-bit OTP register||√|
|DS1972||2D;||1Kb EEPROM memory||√|
|DS1973||23||4Kb EEPROM memory|
|DS1977||37||Password-protected 32kB (bytes) EEPROM||√|
|DS1982||09||1Kb EPROM memory|
|DS1885||0B||16Kb EPROM memory|
|DS1990A||01||1-Wire address only|
|DS1990R||01||1-Wire address only|
|DS1991||02||Multikey iButton, 1152-bit secure memory||Not recommended for new designs, see application note 4421, "Alternatives to the DS1991L MultiKey iButton®" for alternatives.|
|DS1992||08||1Kb NV RAM memory|
|DS1993||06||4Kb NV RAM memory|
|DS1994||04||4Kb NV RAM memory and clock, timer, alarms||Not remommended for new designs, see application note 4506, "Alternatives to the DS1994L 4Kb Plus Time Memory iButton®" for alternatives.|
|DS1995||0A||16Kb NV RAM memory|
|DS1996||0C||64Kb NV RAM memory|
|DS2401||01||1-Wire address only|
|DS2404||04||4Kb NV RAM memory and clock, timer, alarms||Not recommended for new designs|
|DS2406||12||1Kb EPROM memory, 2-channel addressable switch|
|DS2408||29||8-channel addressable switch||√|
|DS2409||IF||Dual switch, coupler||Not recommended for new designs|
|DS2411||01||Low-voltage, unique 64-bit serial ROM number (requires VDD connection)||√|
|DS2413||3A||Dual-channel addressable switch||√|
|DS2417||27||RTC with interrupt|
|DS2422||41||High-capacity Thermochron/Hygrochron (temperature and humidity) datalogger||√||Not recommended for new designs|
|DS2430A||14||256-bit EEPROM memory and 64-bit OTP register||√||Not recommended for new designs|
|DS2431||2D||1Kb EEPROM memory||√|
|DS2432||33||1Kb EEPROM memory with SHA-1 engine|
|DS2433||23||4Kb EEPROM memory|
|DS2502||09||1Kb EPROM memory|
|DS2505||0B||16Kb EPROM memory|
|DS2703||34||Battery-packed authentication IC|
|DS2740||36||1-Wire coulomb counter (high precision)|
|DS2762||30||1-Wire battery monitor and protector|
|DS2775||32||Stand-alone 1-Wire fuel gauge|
|DS2781||3D||Stand-alone fuel gauge IC|
|DS28E04-100||1C||4Kb EEPROM memory, two-channel addressable switch, 7 address pins||√|
|DS28EA00||42||1-Wire digital thermometer with sequence detect and PIO||√|
|DS28EC20||43||20Kb 1-Wire EEPROM||√|
Note: New 1-Wire devices are constantly added to the product line. Newer parts may not be in this list. Look for an 'Improved Network Behavior' section in the device's data sheet to see if the device incorporates the new extended network front-end.
The new features in the Extended Network Standard are only fully active during standard speed communication, not in overdrive. Adding these features to the 1-Wire front-end can affect the 1-Wire timing specification. Specifically, the new standard introduces an EC table parameter, tREH, that represents the rising-edge hold-off time. This hold-off behavior increases the low time generated by the master and required in a read bit, tRL. See Table 2.
Field experience with applications using long lines to communicate with 1-Wire devices demonstrates the importance of adequate recovery between bits. As a result, all of the extended-network devices have longer recovery times, tREC. The recovery-time specification for all devices (standard and extended network) is given for one device on a 1-Wire bus. For a guide to extending this specification to multiple devices, see application note 3829, "Determining the Recovery Time for Multiple-Slave 1-Wire Networks."
Devices that incorporate slew control on the presence pulse include a parameter, tFPD, for Presence Detect Fall Time. While controlling the slew creates less reflections on long lines, it has a significant effect on the window in which a master can detect the presence pulse. Impedance matching on the 1-Wire master can be equally effective in controlling these reflections without incurring the slew-rate delay. Consequently, future devices may not incorporate the presence-pulse slew-rate feature.
|tREC (before reset)||Overdrive||Min||1µs||5µs|
|tREH||Standard||Min||-||Varies from 0.5µs to 0.6µs|
|Standard||Max||-||Varies from 2µs to 5µs|
|Overdrive||Min||-||Varies from 0µs to 0.6µs|
|Overdrive||Max||-||Varies from 0µs to 2µs|
|*See the device data sheets for the actual tREH values.|
A 1-Wire master can work with both standard and extended-network devices. Accommodating the extended-network devices is as simple as extending recovery time between bits and using a longer start pulse for a read bit, tRL. While the longer recovery will slow the throughput, the change in the read-bit start pulse will not affect the throughput. For networks with devices using presence-pulse slew control, tFPD, care must be taken to select the sample point for the presence pulse. For some devices and voltages the sample range may be restrictive.
Application note 126, "
Also see: all 1-Wire devices