RE: RS485 communication

David Woodhouse (dwmw2@infradead.org)
16 Mar 2003 10:05:31 +0000

On Sun, 2003-03-16 at 00:56, Alan Cox wrote:
> RS485 supports CDMA, thats more than enough to implement ppp nicely, all
> you have to do is a little abuse in the app or driver layer to block
> sending when carrier is asserted

Note you don't need any separate lines for this. If someone else is
transmitting a zero while you are also transmitting a zero, that's fine
and you didn't stomp on each other. If someone else is transmitting a
zero while you are transmitting a one, you won and a one was
transmitted, and they back off. If they transmit a one while you
transmit a zero, then they won :)

That's how CAN does it, IIRC. I don't believe it actually requires
synchronous clocks.

-- 
dwmw2




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