Post by thread:[EE]: RS-485 Chips

Can anyone suggest some RS-485 chips Does anyone know what they actually do (l think they drive the line with current rather than voltage?) and can they be emulated with transistors or the like ? If anyone has any circuits of line drivers for this application can you let me know please. Also need a decent australian supplier and prices (rough)... thank you Paul Drummond spam_OUTgeniesysTakeThisOuTalphalink.com.au -- http://www.piclist.com#nomail Going offline? Don't AutoReply us! use .....listservKILLspam@spam@mitvma.mit.edu?bodyT%20PICList%20DIGEST

> Can anyone suggest some RS-485 chips MAX485 for half duplex, MAX489 for full duplex. > Does anyone know what they actually do (l think they drive the line with current rather than voltage?) > and can they be emulated with transistors or the like ? If anyone has any circuits of line drivers for this > application can you let me know please. If you want example circuits implimenting the above, see their data sheets at: http://pdfserv.maxim-ic.com/arpdf/1112.pdf Erm... they aren't "current drivers" like I think you may be thinking. It is a ruggedized voltage controlled bus. You may be thinking of a "4-20 current loop" or just "current loop", which is a completely different beast. You may wish to read National Semiconductor's application notes on RS-485. I have found them quite illuminating. http://www.national.com/apnotes/RS-485.html You could certainly emulate RS-485 compliant transmitters with a pair of FETs. The receiver would be more difficult, I imagine. One might start with a comparator and work on from there. The nice thing about 485 IC's is how relatively rugged they are. > Also need a decent australian supplier and prices (rough)... Sorry, can't help you there. You might try looking at: http://www.findchips.com and http://www.partminer.com for a program that will search suppliers and distributers for stock given a particular part number or description string. -d -- http://www.piclist.com#nomail Going offline? Don't AutoReply us! use listservKILLspammitvma.mit.edu?body=SET%20PICList%20DIGEST

>Can anyone suggest some RS-485 chips MAX485,LT485,SN75176... I use the SN75176 because here it's the cheapest one. Take a look at National,Maxim and Linear websites there's a lot of info out there I suggest National's app-note 1057 ("Ten ways to bulletproof RS-485 Interfaces") http://www.national.com >Does anyone know what they actually do (l think they drive the line with >current rather than voltage?) Multidrop serial interfaces. Diferential voltage. > and can they be emulated with transistors or the like ? Why bother? these things are cheap. >If anyone has any circuits of line drivers for this application can you >let me know please. On the datasheets there's some examples. look also on http://www.lvr.com and http://www.rs485.com >Also need a decent australian supplier and prices (rough)... Sorry mate, I'm on the other side of the globe <G> -- http://www.piclist.com#nomail Going offline? Don't AutoReply us! use .....listservKILLspam.....mitvma.mit.edu?body=SET%20PICList%20DIGEST

I'd say there's no one device for every application, since there is a broad spectrum of uses. Speeds go from typical asynch speeds to 10M or higher. Half duplex is very common and there is a choice of 8 pin devices with the same pinout. You might look at your sources to see what is readily available? The driver has to drive into 60 ohms as a long twisted pair being used at high speed would have a 120 ohm terminating resistor at each end. Typical serial rates are low enough that operation without terminations can be achieved over short distances using slew-rate-limited outputs. The reciever is essentially a comparator. The margin is fairly narrow, so a balanced input is essential. Some recievers have added value by going into a guaranteed state when the line is not being driven (some of the Maxim range) which is invaluable when using asynch serial, since a false transition may be mistaken for a start bit, causing the real start bit to be missed. Oliver. {Original Message removed}

<snip> > The reciever is essentially a comparator. The margin is fairly narrow, so a > balanced input is essential. Some recievers have added value by going into > a guaranteed state when the line is not being driven (some of the Maxim > range) which is invaluable when using asynch serial, since a false > transition may be mistaken for a start bit, causing the real start bit to be > missed. National Semi also makes a Dominant Mode transceiver. This allows you to "fail-safe bias" a 485ish bus. This particular chip is targeted toward class 2 vehicle communication; j1708 and the like. http://www.national.com/pf/DS/DS36277.html -d -- http://www.piclist.com#nomail Going offline? Don't AutoReply us! use EraseMElistservspam_OUTTakeThisOuTmitvma.mit.edu?body=SET%20PICList%20DIGEST

Try the Maxim web site. Like the MAX232 they also make a MAX485. The RS485 protocol allows for multiple nodes on the one bus, a bit like the old 10BASE2 or coax ethernet. It is common in industrial applications that use PLC and the likes. Very handy. Try http://www.maxim-ic.com and search for max485, you will find lots there. Mark ---------------------------------------------------- Mark Thorley Brisbane, Queensland, Australia. _________________________________________________________________________ Get Your Private, Free E-mail from MSN Hotmail at http://www.hotmail.com. Share information about yourself, create your own public profile at http://profiles.msn.com. -- http://www.piclist.com#nomail Going offline? Don't AutoReply us! use listservspam_OUTmitvma.mit.edu?body=SET%20PICList%20DIGEST

Don't forget the ground (common) wire (3rd wire for half duplex or 5th wire for full duplex). Nationals app notes tell You ll about them. I have found the app note '10 ways to bulletproof Your RS485 networ' (or something) to be very usefull. I allways add protection components to my RS232/485 ports in the following manner: Port pin - 3 terminal LCL network - 20 ohm resistor - tranzorb to gnd (and tranzorb to the other line for 485 networks) - 20 ohm resistor - IC pin. Note that the tranzorbs have fairly high capacitance which could reduce maximum baudrate, but I have had good results with up to 115200bps. Normally don't go higher than 9600, though. Date sent: Thu, 28 Sep 2000 02:22:19 +1000 Send reply to: pic microcontroller discussion list <@spam@PICLISTKILLspamMITVMA.MIT.EDU> From: Paul <KILLspamgeniesysKILLspamALPHALINK.COM.AU> Subject: [EE]: RS-485 Chips To: RemoveMEPICLISTTakeThisOuTMITVMA.MIT.EDU {Quote hidden}> Can anyone suggest some RS-485 chips > > Does anyone know what they actually do (l think they drive the line > with current rather than voltage?) and can they be emulated with > transistors or the like ? If anyone has any circuits of line drivers > for this application can you let me know please. > > Also need a decent australian supplier and prices (rough)... > > thank you > > Paul Drummond > spamBeGonegeniesysspamBeGonealphalink.com.au > > -- > http://www.piclist.com#nomail Going offline? Don't AutoReply us! > use TakeThisOuTlistservEraseMEspam_OUTmitvma.mit.edu?body=SET%20PICList%20DIGEST > ============================== Ruben Jvnsson AB Liros Elektronik Box 9124, 200 39 Malmv, Sweden TEL INT +46 40142078 FAX INT +46 40947388 RemoveMErubenTakeThisOuTpp.sbbs.se ============================== -- http://www.piclist.com hint: To leave the PICList piclist-unsubscribe-requestEraseME.....mitvma.mit.edu

www.maxim-ic.com Paul wrote: {Quote hidden}> Can anyone suggest some RS-485 chips > > Does anyone know what they actually do (l think they drive the line with current rather than voltage?) and can they be emulated with transistors or the like ? If anyone has any circuits of line drivers for this application can you let me know please. > > Also need a decent australian supplier and prices (rough)... > > thank you > > Paul Drummond > EraseMEgeniesysalphalink.com.au > > -- > http://www.piclist.com#nomail Going offline? Don't AutoReply us! > use RemoveMElistservEraseMEEraseMEmitvma.mit.edu?body=SET%20PICList%20DIGEST -- http://www.piclist.com hint: To leave the PICList RemoveMEpiclist-unsubscribe-requestspam_OUTKILLspammitvma.mit.edu