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Re: RS485
- To: ukha_d@xxxxxxx
- Subject: Re: RS485
- From: Nigel Orr <Nigel.Orr@xxxxxxx>
- Date: Tue, 11 Apr 2000 08:52:43 +0100
- Delivered-to: rich@xxxxxxx
- Delivered-to: mailing list ukha_d@xxxxxxx
- Mailing-list: list ukha_d@xxxxxxx; contact
ukha_d-owner@xxxxxxx
- Reply-to: ukha_d@xxxxxxx
At 20:14 10/04/00 +0100, you wrote:
>I am wanting to read up about RS485 (how it works, how to connect
devices to
>it, etc) and wondered if anybody had any pointers they were willing to
>share?
It's worth noting that it's less of a 'standard' than RS-232. Basically,
it's just RS-232 with balanced signalling, so it can cope with longer
distances, higher speed and multiple transmitters on the same 'bus'. If
you come across references to RS-422, that's the same thing, but without
the multiple transmitters.
How handshaking and bus contention is handled is up to the individual
implementation (or if there is a standard, I've never been fortunate enough
to see it...). One common implementation is DMX-512 (which is relevantish
to home automation), which was developed to control stage lighting dimmers.
But RS-485 is just an electrical standard, doesn't specify data formats etc
etc. What are you hoping to do with it? I might have some specifics I can
dig out somewhere (last time I used it was last year, to build a parallel
port to RS-485 to parallel port converter to run parallel port-controlled
equipment through 150m of cable).
Nigel
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