r/BACnet

RS-485 Polarity
▲ 9 r/BACnet+2 crossposts

RS-485 Polarity

Anybody familiar with this diagram of a RS-485 waveform (from Wikipedia) ?

https://preview.redd.it/0fconor22p9h1.png?width=534&format=png&auto=webp&s=0d69b3758c128d5f2f3eb5c0bb677b8be752afbe

and this diagram from the actual EIA/TIA-485 specification ( So U+ can be aligned with A )

https://preview.redd.it/73oi539j2p9h1.png?width=366&format=png&auto=webp&s=69a5d285b78343aeed4f725435353da98ef5c00b

which is then followed up with this table in the Wikipedia article

https://preview.redd.it/xpf6fks72p9h1.png?width=668&format=png&auto=webp&s=a91c7d942ae967bce75f9b83a1e692d76596e9f3

Surely this is flat-out contradictory ? (All "Lows" and "Highs" should be inverted)

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u/BACnetEd — 11 days ago