AN3684| Application Note
Maxim > App Notes > 1-WIRE DEVICES Keywords: i2c, 1-wire, bridge, ds2482, line driver, guide, slew, waveforms, master
Nov 07, 2005
APPLICATION NOTE 3684
How to Use the DS2482 I C 1-Wire Master
Abstract: The DS2482 is an I2C bridge to the 1-Wire network protocol. As a bridge, the DS2482 allows any host with I2C communication to generate properly timed and slew-controlled 1-Wire waveforms. This Application Note is a user's guide for the DS2482 I2C 1-Wire Line Driver, and provides detailed communication sessions for common 1-Wire master operations.
1. Introduction
The 1-Wire communication protocol can be generated using the DS2482, which is a bridge for I2C communication to a 1-Wire network. This bridge allows any host with I2C to generate properly timed 1-Wire waveforms. See Figure 1 for a simplified diagram of the DS2482 configuration. Implementing this protocol and navigating the available DS2482 commands can be time-consuming and confusing. This document presents an efficient implementation of the basic and extended 1-Wire operations using the DS2482. The construction of I2C input packets to handle 1-Wire communication is explained. These operations provide a complete foundation to perform all the functions for current and future 1-Wire devices. Abstracting the 1-Wire operations in this fashion leads to 1-Wire applications that are independent of the 1-Wire master type. This document complements the DS2482 data sheet, but does not replace it. The DS2482 is available in two configurations, a singlechannel 1-Wire master (DS2482-100) and an eight-channel 1-Wire mast
er (DS2482-800).
Figure 1. Simplified illustration of DS2482 function as a bridge for I2C communication and a 1-Wire network.
2. The 1-Wire Interface
There are a few basic 1-Wire functions, called primitives, which an application must have in order to perform any 1-Wire operation. This first function resets all the 1-Wire slaves on the bus, readying them for a command from the 1-Wire master. The second function writes a bit from the 1-Wire master to the slaves, and the third reads a bit from the 1-Wire slaves. Since the 1-Wire master must start all 1-Wire bit communication, a 'read' is technically a 'write' of a single bit with the result sampled. Almost all other 1-Wire operations can be constructed from these three operations. For example, a byte written to the 1-Wire bus is just eight single bit writes. The 1-Wire Search Algorithm can also be constructed using these same three primitives. The DS2482 incorporates a search using the 1-Wire triplet command, which greatly reduces the communication required to do a search. Table 1 shows the three basic primitives (OWReset, OWWriteBit/OWReadBit, and OWWriteByte/OWReadByte), along with three other useful func
tions (OWBlock, OWSearch, msDelay) that together make up a core set of basic 1-Wire operations. These operation names will be used throughout the remainder of this document. Table 1. Basic 1-Wire Operations Operation Description OWReset OWWriteBit/OWReadBit OWBlock OWSearch msDelay Sends the 1-Wire reset stimulus and check for pulses of 1-Wire slave devices. Sends or receives a single bit of data to the 1-Wire bus. Sends and receives multiple bytes of data to and from the 1-Wire bus. Performs the 1-Wire Search Algorithm (see Application Note 187 mentioned above). Delays at least the specified number of milliseconds.
OWWriteByte/OWReadByte Sends or receives a single byte of data to the 1-Wire bus.
Extended 1-Wire functions (such as overdrive communication functions) are not covered in the basic operations in the table above.
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