Re: RS-485 arrangements

Richard Henry wrote:
I have long been familiar with RS-485 wired as a single differential
pair connected to all the devices and termination at the both ends,
however "end" may be defined. I have recently been looking into a 4-
wire "full-duplex" implementation. However, it seems to be full-
duplex only if there are only two devices attached. Otherwise, there
appears to be a need to designate one device as the master (the device
to whose receiver all the other drivers are connected) and the rest as
slaves.

Unless there is some clever arrangement of which I am ignorant. Any
comments?

For reference:

http://datasheets.maxim-ic.com/en/ds/MAX3483-MAX3491.pdf
http://www.bb-elec.com/tech_articles/rs422_485_app_note/system_configuration.asp

slave devices don't talk unless spoken to.
this means, You need a protocol.
MODBUS is a good example.. Look it up.


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