User manual

1-Wire Application Guide v1.04 Page 8 of 41
Figure 2 1-Wire Star Network
A star network is somewhat more complex than a bus network. A typical star
network is shown in Figure 2.
An advantage of a star network is that it can be easier to physically wire. Many
sensor locations can be reached, and added, by stringing a cable from the main
point to the sensor. Also, a break of one sensor’s wiring will not affect other
sensors.
The biggest disadvantage of a star network, however, is the electrical noise that
can be introduced if not properly connected. Electrical noise will result from 1-
Wire communication pulses traveling down different branches of the star, which
generally have different lengths, and returning at different times. This is called
reflection. Fortunately, adding a series resistor to all the branches of the network
can minimize the reflections. These resistors reduce the reflections, and hence
the electrical noise, and therefore make communications somewhat more robust.
Figure 3 shows where the resistors belong. Generally, a 100-ohm resistor is
recommended for this.