Dallas 1-Wire Master-Slave System

Posted in Device Interfacing
On Friday, August 18, 2006

1-Wire® from Dallas Semiconductor is a signaling protocol to enable bidirectional communication in single line/wire system (1 line for bidirectional data, 1 line for grounding ). 1-Wire® is a Master-Slave system, where one master communicate to one or more device(s) one device at a time. Microcontroller usually act as master. The slave can be I/O or memory devices, such as sensors, RTC, ADC, ROM, EEPROM, etc.

There are four basic operation of 1-Wire® master device:

Reset bus
Write logic ‘1′ bit to bus
Write logic ‘0′ bit to bus
Read bus

Following table from Dallas describes those operations:

Operation	Description	Implementation
Write “1″	Send a ‘1′ bit to the 1-Wire slaves (Write 1 time slot)	Drive bus low, delay A Release bus, delay B
Write “0″	send a ‘0′ bit to the 1-Wire slaves (Write 0 time slot)	Drive bus low, delay C Release bus, delay D
Read bit	Read a bit from the 1-Wire slaves (Read time slot)	Drive bus low, delay A Release bus, delay E Sample bus to read bit from slave Delay F
Reset	Reset the 1-Wire bus slave devices and ready them for a command	Delay G Drive bus low, delay H Release bus, delay I Sample bus, 0 = device(s) present, 1 = no device present Delay J

A common microprocessor can be program to be Master of 1-Wire® line, but these requirements should be satisfied:

The communication port must be bidirectional, its output is open-drain, and there is a weak pull-up on the line.
The system must be capable of generating an accurate and repeatable 1µs delay for standard speed and 0.25µs delay for overdrive speed.
The communication operations must not be interrupted while being generated.

Here are some Dallas devices which use 1-Wire® bus

DS18S20 Parasite-Power Digital Thermometer
DS1904 RTC iButton
DS2408 8-Channel Addressable Switch
DS2413 Dual Channel Addressable Switch
DS2417 Time Chip With Interrupt
DS2422 Temperature/Data Logger with 8kB Datalog Memory
DS2423 4 kbit RAM with Counter
DS2430A 256 bit EEPROM
DS2431 1024-Bit EEPROM
DS2432 1kb Protected EEPROM with SHA-1 Engine
DS2450 Quad A/D Converter
DS2480B Line Driver with Load Sensor
DS2890 Digital Potentiometer
etc..

For more information about 1-Wire®, see Dallas application note, 1-Wire® master communication routines in C language. See also how to implement 1-Wire® in PIC Microcontroller.

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