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Keywords:
1wire, 1-Wire master, network, topology, CAT5, CAT5e, category 5e, category 5, reliable,
reliability, maximum distance
TUTORIAL 148
GUIDELINES FOR RELIABLE LONG LINE 1-
WIRE NETWORKS
Abstract: The 1-Wire
protocol was originally designed to facilitate communication with nearby devices on
a short connection. 1-Wire was also a way to add auxiliary memory on a single microprocessor port pin.
Methods were later developed to extend the 1-Wire protocol to network applications well beyond the size
of a circuit board. This document discusses various aspects of 1-Wire networks and provides design
guidelines for their reliable operation. Several appendices address fine-tuning the 1-Wire bus interface
and illustrate 1-Wire communication waveforms in various conditions.
Introduction
The 1-Wire protocol was originally designed for communication with
nearby devices on a short connection, such as adding auxiliary memory
on a single microprocessor port pin. As the use of 1-Wire devices
increased, methods were developed to extend the 1-Wire protocol to
networked applications well beyond the size of a circuit board. A 1-Wire
network is a complex arrangement of 1-Wire devices, communication
lines, and connections. Every 1-Wire network is different, often both in
topology (layout) and hardware.
A proper match among network components (i.e., master, network
cabling, and 1-Wire slave devices, "slaves") is the precondition for
reliable 1-Wire operation. When bus masters are improperly designed
or implemented, or when masters intended for short-line use are
pressed into service with greatly extended communication lines, then
satisfactory performance cannot always be expected.
This application note presents the results of a project to characterize
the operation of 1-Wire networks of various forms, sizes, and
populations. It also provides working parameters for reliable network
operation. Some of the aspects discussed here are not critical in short-
line applications, e.g. networks of less than 1 meter. Appendices A
through D address fine-tuning the 1-Wire bus interface and illustrate 1-
Wire communication waveforms in various conditions.
Network Description
The scope of this document is limited to 1-Wire networks that use
Category 5e, twisted-pair copper wire and have 5V bus power supplied
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