By physical star wiring topology I simply mean the mechanical wiring layout — how the cables are physically routed.
In contrast, the electrical bus topology describes how the signal actually behaves on the bus from an electrical point of view (line reflections, capacitance, branch stubs, etc.).
With the 1-Wire bus these two things often become problematic when they are the same.
A true electrical star topology tends to cause signal integrity issues because every branch behaves like a stub.
The approach shown here avoids that situation by using one sensor per bus, so each bus electrically remains a simple line, while the overall installation can still be arranged physically like a star.
There is a reason why these different types of plans exist
This post is totally irrelevant to the last 7.
You suggest that a star topology is practical when Maxim clearly states that it would be problematic.
For anyone who really wants to learn how to design a robust, error free and reliable 1-wire bus, I suggest you spend some time reading the 100+ app notes and technical articles that Maxim has on the topic.
A star topology does not depend on how many sensors are connected to the bus.
It depends on the wiring. If multiple cable branches leave the same point, it is a star topology — even if each branch contains only a single sensor. In other words: parallel devices are normal in 1-Wire, but parallel cable branches create the star. It's that simple!
Surely you can see the difference between the two topologies. The problem with the star topology at the top is that the equal stub lengths cause the reflections to "pile up" at the junction and create read errors.
It’s just a regurgitation of one of the Maxim app notes.
It all started 30+ years ago when Dallas Semi (hence the DS) introduced the iButton with the 1-wire bus.
