Discovery Checksum Problem Analysis - E1.20 RDM (Remote Device Management) Protocol Forums

Nigel Worsley · September 24th, 2006

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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September 24th, 2006	#1
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.