I want to know how multidrop differs from daisy chain topology? I am using RS 485 standard and modbus protocol for communication. So which topology is best for my requirement ?
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1\$\begingroup\$ What is your requirement, none is specified? \$\endgroup\$– Jack CreaseyCommented Jan 6, 2017 at 7:07
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1\$\begingroup\$ Where did you get the term "daisy chain" from? It can mean the same as "multidrop". \$\endgroup\$– CL.Commented Jan 6, 2017 at 10:07
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3 Answers
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They are the same thing in terms of RS-485. Electrically identical. Multi-drop is the more accepted term.
To put a finer point on it, daisy-chaining is a connection technique whereby one RS-485 adapter is wired directly to the next one, and so on.
The alternative connection technique (which would not be called "daisy chaining" is to have a common bus architecture, and just have each adapter connect to the bus).
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Daisy chain is a topology of connecting more than one device on a single communication line. Further, there are terms of communication called as half duplex and full duplex. RS485 can be operated in both modes depending on 2 wire or 4 wire configuration.
RS485 is always a multidrop bus which means more than one device can transmit data but not all at the same time. In other words, the bus architecture may be comprised of one master and different slaves but communication will happen only between master and only one slave.
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Electrically, they are the same but with a caveat. The stubs should be short as possible to reduce reflection. Traditional point to point "daisy chaining" removes that issue. Ref. https://www.ti.com/lit/an/slla070d/slla070d.pdf
