Re: RS485 resistors

["Frank Mc Alinden" <armagh@xxxxxxx>]

Hi Tony + Ian

When dabbling with rs485 comms i used a circuit from this site . I built
the
same circuit and added a video chip on it so i could display what my
units
were txing on my tv.
rs485 should be wired daisy chained as Ian says although i have
personally
wired security equipment in the field in star configuration and worked
ok............
Have a look its an interesting site ..

http://home.att.net/%7Edennis.shepard/net.htm

Frank Mc

----- Original Message -----
From: <ian.bird@xxxxxxx>
To: <ukha_d@xxxxxxx>
Sent: Thursday, August 15, 2002 7:10 PM
Subject: [ukha_d] RS485 resistors


> Hi Tony
>
> If your wiring is short it probably won't matter. Neither 232 nor
RS485
are
> protocols by the way. You might be down to trial and error with a
scope to
> find out what is going on.
>
> I don't know the units so cannot help there I am afraid.
>
> Ian
>
>
>
>
>
> Hi Ian,
>
> Thanks for the info.
>
> These termination resistors are of concern - do you mean there will
be
some
> in the converter I need to disable (not a problem really) or some in
the
> devices at each end I would have to disable? This _would_ be a problem
as
I
> don't want to take the chance of wrecking expensive kit!!!
>
> Good to know that 485 is robust enough if you don't connect things
up
> properly but......what if it's _not_ 485?
> Is there any way you can think of that I may be ablt to dientify if it
is
> 232/485/any other serial protocol?
>
> thanks,
>
>
> Tony
>
>
> > -----Original Message-----
> > From: Ian B [mailto:Ian@xxxxxxx]
> > Sent: 14 August 2002 19:50
> > To: BUTLER, Tony, FM
> > Subject: RE: [ukha_d] Re: Displays round the house -
architecture...
> >
> >
> > Hi Tony
> >
> > Assuming it is RS485 I would get one of the commercial
> > converters but you
> > will need to have access to the termination resistors somewhere.
These
> > should only be applied at each end of the network. Ask if in
> > doubt when you
> > buy yours. RS485 has a plus and minus rail, plug it in
> > wrongly and it simply
> > doesn't work. Switch the connections and off you go.
> >
> > Other than that cut the cable and plug in.
> >
> > Ian
> >
> > >-----Original Message-----
> > >From: BUTLER, Tony, FM [mailto:Tony.BUTLER@xxxxxxx]
> > >Sent: 14 August 2002 09:13
> > >To: 'Ian@xxxxxxx'
> > >Subject: RE: [ukha_d] Re: Displays round the house -
architecture...
> > >
> > >
> > >Hi Ian,
> > >
> > >> -----Original Message-----
> > >> From: Ian B [mailto:Ian@xxxxxxx]
> > >> I also have a 232 to 485 converter running as an
interface
> > between my
> > >> prototype networks :-))
> > >
> > >This is of interest to me.
> > >My Linn knekt system uses, I think (well, others think
> > anyway) 485 because
> > >power and data are sent over cat5 to wall moounted room
control units
> > >(RCUs).
> > >I would like to look at say using a PC to emulate an RCU
> > and/or to send IR
> > >for devices not supported by the version of Linn software
> > running on my
> > >system.
> > >Now Linn are about as open as Microsoft when it comes to
> > divulging details
> > >of their systems, so it's reverse-engineer or nothing.
> > >
> > >Anyway, to the point: To do this I would need to 'sniff'
> > the signals being
> > >sent to the RCU and to do this I would, I guess need to
> > convert from 485 to
> > >232 so the PC can see the data and later, if I get as far
as
> > emulating an
> > >RCU, I would need to do the reverse.
> > >How easy/difficult is it to build such a converter? Does
> > your one do both
> > >way comms?
> > >How easy do you think it would be to basically bung one
in
> > >parallel with the
> > >existing system so I can sniff the data being sent over
the
> > 'live' system./
> > >I've seen 232 sniffers mentioned in places before, but I
> > guess I'd need a
> > >485 sniffer......
> > >
> > >Any thoughts would be most appreciated.
> > >
> > >thanks,
> > >
> > >
> > >Tony
>
>
>
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