The easiest thing to do is use repeaters! This isolates the slaves from the network.
Whatever you do, you must still adjust the software to handle non-responding nodes. You can isolate the channels, but then you must choose a channel in software, send a message, receive it etc. A lot of software changes. And if you run a multitasking system like Bitbus, it will not work. With repeaters you do not have to change the software. May look somewhat expensive at first sight, but is very fast to install, costs you no software and may therefor even be a cheap solution. About better electronics: There are many good RS485 transceivers that are ESD and short-circuit proof. Also be sure to use shielded cable with twisted pairs, at the end a resistor of the characteristic impedance of 100 ohm or 120 ohm (depends on the cable). And optically isolate things to prevent currents through the 0V/Ground line. Feel free to ask me any information. Regards, Pieter Hoeben Date sent: Wed, 24 Aug 2005 02:49:21 -0800 To: Multiple recipients of list CHIPDIR-L <[email protected]> Send reply to: [email protected] Organization: Fat City Network Services, San Diego, California > Hello, > > > So basically this is a RS485 bus system with 120 nodes that > must have very high reliability? > > A. YES > > >Use decent RS485 drivers > that are short-circuit and ESD proof, there are several, and > I do not think your system will fail. I have worked with RS485 > Bitbus industrial systems for years, and found it very reliable. > That is why it is used a lot in German telecom. One line > even 12 kilometers long. > > A. Lucky you!. We have had all sorts of problems. > It only takes one RS485 driver to die, in order to pull down the whole system, > and we ARE eliminating this, but separating the channels. > > I am looking for ideas for the multiplexer. > > Analogue Devices, ADG725 is a 32 channel analogue mux. This is the best > we've found so far. > > -----Original Message----- > Pieter Hoeben > Sent: 23 August 2005 22:04 > To: Multiple recipients of list CHIPDIR-L > > > Hi, > > So basically this is a RS485 bus system with 120 nodes that > must have very high reliability? Use decent RS485 drivers > that are short-circuit and ESD proof, there are several, and > I do not think your system will fail. I have worked with RS485 > Bitbus industrial systems for years, and found it very reliable. > That is why it is used a lot in German telecom. One line > even 12 kilometers long. > > Or are you "hot-swapping", plugging and unplugging? > > Does your system still live if one node goes down? Or are > you calibrating 120 machines in for example a temperature > calibration? In that case you must adjust your software so it > can handle nodes that are down. > > You could also do 30 channels in blocks of 4, and accept that > when one goes down, all 4 go down? Or 15 of 8? In that > case the logic may get easier. > > What exactly are you building? > > In case of 120 RS485 slaves, you would only have to use > repeaters to keep other equipment alive!!!!!!! My motto: > Keep It Simple (what ain't there won't crash) > > Regards, > Pieter Hoeben > > > Date sent: Tue, 23 Aug 2005 09:04:22 -0800 > To: Multiple recipients of list CHIPDIR-L > <[email protected]> > Send reply to: [email protected] > Organization: Fat City Network Services, San Diego, California > > > Hi, > > > > It's a calibration system, and as such it requires high reliability. > > > > Networking and addressing leaves the system open to problems such as > > if one RS485 chip goes short circuit, for example, it will bring the whole > > network down and screw up the (lengthy) calibration process > > > > Therefore IT MUST be designed this way, unless you can think of anything > > better > > > > Separating each channel isolates unit specific problems to just that channel > > > > > > > > -----Original Message----- > > Declan Moriarty > > Sent: 23 August 2005 17:49 > > To: Multiple recipients of list CHIPDIR-L > > > > > > Recently, Somebody Somewhere wrote these words > > > Hi, > > > > > > Thanks. > > > > > > I think I should have been more specific. > > > > > > We've got an RS485 comms pair, which we want to multiplex between 120 > > > RS485 pairs. > > > > > > I.e. 120 channels to 1 (or 240 to 2 in terms of actual wires). > > > > > > Ive seen a 32 channel analogue switch from Analogue devices, but im > > > unsure as to whether an Analogue switch will be ok? > > > > > > > To quote the Irishman who was asked for directions to somewhere: > > > > "You know... If I was you, I wouldn't start from here at all!" > > > > You are never going to stand up 1-->120 in an RS485 link without such > > heartache as to justify a sane design. What's your baud rate? You would > > also need sample & holds everywhere. Network the things and address > > them. Start over, my friend. > > > > Imagine when you get the complaint "Channel 87 goes intermittent after > > about 5 minutes" How will you sort that? > > > > BTW, the trick with analogue switches is never bring the input below the > > negative rail. > > > > > > > > -- > > > > > > > > With best Regards, > > > > > > Declan Moriarty. > > -- > > Author: Declan Moriarty > > INET: [EMAIL PROTECTED] > > > > Fat City Hosting, San Diego, California -- http://www.fatcity.com > > --------------------------------------------------------------------- > > To REMOVE yourself from this mailing list, send an E-Mail message > > to: [EMAIL PROTECTED] (note EXACT spelling of 'ListGuru') and in > > the message BODY, include a line containing: UNSUB CHIPDIR-L > > (or the name of mailing list you want to be removed from). You may > > also send the HELP command for other information (like subscribing). > > -- > > Author: Darren Logan > > INET: [EMAIL PROTECTED] > > > > Fat City Hosting, San Diego, California -- http://www.fatcity.com > > --------------------------------------------------------------------- > > To REMOVE yourself from this mailing list, send an E-Mail message > > to: [EMAIL PROTECTED] (note EXACT spelling of 'ListGuru') and in > > the message BODY, include a line containing: UNSUB CHIPDIR-L > > (or the name of mailing list you want to be removed from). You may > > also send the HELP command for other information (like subscribing). > > > > > > > ______________________________________________ > > Hoeben Electronics Phone: +31 6 51590081 > Ronkert 44 Fax: +31 13 5096025 > 5094 EW Lage Mierde Private: +31 13 5096200 > The Netherlands E-mail: [EMAIL PROTECTED] > http://www.hoeben.com > ______________________________________________ > > > -- > Author: Pieter Hoeben > INET: [EMAIL PROTECTED] > > Fat City Hosting, San Diego, California -- http://www.fatcity.com > --------------------------------------------------------------------- > To REMOVE yourself from this mailing list, send an E-Mail message > to: [EMAIL PROTECTED] (note EXACT spelling of 'ListGuru') and in > the message BODY, include a line containing: UNSUB CHIPDIR-L > (or the name of mailing list you want to be removed from). You may > also send the HELP command for other information (like subscribing). > -- > Author: Darren Logan > INET: [EMAIL PROTECTED] > > Fat City Hosting, San Diego, California -- http://www.fatcity.com > --------------------------------------------------------------------- > To REMOVE yourself from this mailing list, send an E-Mail message > to: [EMAIL PROTECTED] (note EXACT spelling of 'ListGuru') and in > the message BODY, include a line containing: UNSUB CHIPDIR-L > (or the name of mailing list you want to be removed from). You may > also send the HELP command for other information (like subscribing). > > ______________________________________________ Hoeben Electronics Phone: +31 6 51590081 Ronkert 44 Fax: +31 13 5096025 5094 EW Lage Mierde Private: +31 13 5096200 The Netherlands E-mail: [EMAIL PROTECTED] http://www.hoeben.com ______________________________________________ -- Author: Pieter Hoeben INET: [EMAIL PROTECTED] Fat City Hosting, San Diego, California -- http://www.fatcity.com --------------------------------------------------------------------- To REMOVE yourself from this mailing list, send an E-Mail message to: [EMAIL PROTECTED] (note EXACT spelling of 'ListGuru') and in the message BODY, include a line containing: UNSUB CHIPDIR-L (or the name of mailing list you want to be removed from). You may also send the HELP command for other information (like subscribing).
