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Old September 24th, 2006   #3
Nigel Worsley
Junior Member
Join Date: Jun 2006
Location: London
Posts: 13

You are forgetting two things:

The SN75176 is a very old device, and more modern transceivers usually guarantee that a 0V input will give a high output. The MAX485 datasheet says: "The receiver input has a fail-safe feature that guarantees a logic-high output if the input is open circuit."

Also, the controller's terminating network is required to put a slight bias on the line.

Either of these things would ensure that a collision by drivers of exactly equal strength would result in a one being received.
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