Re: Effect of a rs485 damaged driver

From: Tim Shoppa (shoppa_at_trailing-edge.com)
Date: 09/24/04 

Date: 24 Sep 2004 05:16:32 -0700

Tim Wescott <tim@wescottnospamdesign.com> wrote in message news:<10l616hck5ocsa1@corp.supernews.com>...
> > Some bus networks have receivers that can issue an alarm if one of the
> > bus lines is stuck high/low or they see meaningless jabber. Haven't
> > seen this for RS-485 although some software will issue somewhat meaningful
> > alarms when they cannot see their own transmissions :-).
>
> Asynchronous serial receivers can detect framing errors, and any
> protocol should include at least a checksum on messages -- you can alarm
> on either bad checksums, framing errors, or the line going silent.

Yeah, but still RS-485 doesn't have all the features that Ethernet
over say 10Base2 has (In thinking of the OP's request, desirable
features would include collision detection and hubs that can autopartition
to isolate a jabbering leg).

I know, some of that can be layered on top of RS-485, but the
protocol itself is just electrical and doesn't talk about how to
layer that all on. (Besides the electrical part doesn't specify
collision detect even though a couple of manufacturers make parts
that support detection of fighting drivers.) Not to bad-mouth RS-485,
there's far worse electrical interfaces in everyday use!

Tim.