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2007-04-12 by magzky02
hello folks, I am using a micocontroller to communicate with 18 other microcontrollers via rs489. Using the IC MAX3088, and a 100 ohm resistor across A and B.. Since there are 19 MAX3088, there are also 19 100 ohm in parallel. IS there something wrong with this? the resulting resistance is only about 5.3 ohms. thanks for advice mago
2007-04-12 by John Samperi
At 04:28 PM 12/04/2007, you wrote: >Since there are 19 MAX3088, there are also >19 100 ohm in parallel. IS there something wrong with this? t Yes!! The 120 Ohm resistor goes ONLY at the end of the line and another one at the start of the line plus the line biasing network. Regards John Samperi ******************************************************** Ampertronics Pty. Ltd. 11 Brokenwood Place Baulkham Hills, NSW 2153 AUSTRALIA Tel. (02) 9674-6495 Fax (02) 9674-8745 Email: john@ampertronics.com.au Website http://www.ampertronics.com.au *Electronic Design * Custom Products * Contract Assembly ********************************************************
2007-04-12 by Andreas Stemmer
magzky02 wrote: > I am using a micocontroller to communicate with 18 other > microcontrollers via rs489. Using the IC MAX3088, and a 100 ohm > resistor across A and B.. Since there are 19 MAX3088, there are also > 19 100 ohm in parallel. IS there something wrong with this? Yes, for a RS485 bus, you usually have one 120 ohm termination resistor on each end, not on each transceiver. You should also think about biasing the bus lines in order to have a defined state when no transmitter is active. Look at some of the available RS485 application notes. AS
2007-04-12 by mago Umandam
Ohhh... thanks you for your advice... ;)
regards
mago
Andreas Stemmer <groovingandi@gmx.de> wrote:
magzky02 wrote:
> I am using a micocontroller to communicate with 18 other
> microcontrollers via rs489. Using the IC MAX3088, and a 100 ohm
> resistor across A and B.. Since there are 19 MAX3088, there are also
> 19 100 ohm in parallel. IS there something wrong with this?
Yes, for a RS485 bus, you usually have one 120 ohm termination resistor
on each end, not on each transceiver. You should also think about
biasing the bus lines in order to have a defined state when no
transmitter is active.
Look at some of the available RS485 application notes.
AS
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[Non-text portions of this message have been removed]2007-04-12 by Alex Gibson
mago Umandam wrote: > > Ohhh... thanks you for your advice... ;) > > regards > > mago > > > Andreas Stemmer <groovingandi@gmx.de> wrote: > magzky02 wrote: >> I am using a micocontroller to communicate with 18 other >> microcontrollers via rs489. Using the IC MAX3088, and a 100 ohm >> resistor across A and B.. Since there are 19 MAX3088, there are also >> 19 100 ohm in parallel. IS there something wrong with this? > > Yes, for a RS485 bus, you usually have one 120 ohm termination resistor > on each end, not on each transceiver. You should also think about > biasing the bus lines in order to have a defined state when no > transmitter is active. > > Look at some of the available RS485 application notes. > > AS Circuit cellar have a good rs485 doc by Bob Perrin http://www.circuitcellar.com/library/ccofeature/perrin0799/c79bp3.htm Just using rs485 myself for a bridge(steel) vibration monitoring system. The painful part is making sure I have proper lightning protection , proper galvanic isolation and grounding. Alex
2007-04-12 by dlc
Yes, the termination resistors go only at the termination points to <hopefully> stop reflections on the transmission lines. They don't go at every node. DLC magzky02 wrote: > hello folks, > > I am using a micocontroller to communicate with 18 other > microcontrollers via rs489. Using the IC MAX3088, and a 100 ohm > resistor across A and B.. Since there are 19 MAX3088, there are also > 19 100 ohm in parallel. IS there something wrong with this? the > resulting resistance is only about 5.3 ohms. > > thanks for advice > > mago > > > > > Yahoo! Groups Links > > > -- ------------------------------------------------- Dennis Clark TTT Enterprises www.techtoystoday.com -------------------------------------------------
2007-04-13 by Aaron
magzky02 wrote: > > I am using a micocontroller to communicate with 18 other > microcontrollers via rs489. Using the IC MAX3088, and a 100 ohm > resistor across A and B.. Since there are 19 MAX3088, there are also > 19 100 ohm in parallel. IS there something wrong with this? the > resulting resistance is only about 5.3 ohms. > Didn't I see this same post on the MSP430 list?? Aaron
2007-04-14 by Robert
Why don't you use I2C to link to other microprocessors? It's more effective, no termination problems to deal with. Robert
> > I am using a micocontroller to communicate with 18 other > > microcontrollers via rs489. Using the IC MAX3088, and a 100 ohm > > resistor across A and B.. Since there are 19 MAX3088, there are also > > 19 100 ohm in parallel. IS there something wrong with this? the > > resulting resistance is only about 5.3 ohms. > >
2007-04-14 by John Samperi
At 09:57 PM 14/04/2007, you wrote: >Why don't you use I2C to link to other microprocessors? The other micros could be a Km away?? Regards John Samperi ******************************************************** Ampertronics Pty. Ltd. 11 Brokenwood Place Baulkham Hills, NSW 2153 AUSTRALIA Tel. (02) 9674-6495 Fax (02) 9674-8745 Email: john@ampertronics.com.au Website http://www.ampertronics.com.au *Electronic Design * Custom Products * Contract Assembly ********************************************************
2007-04-15 by Alex Gibson
Robert wrote: > Why don't you use I2C to link to other microprocessors? It's more > effective, no termination problems to deal with. > > Robert > >>> I am using a micocontroller to communicate with 18 other >>> microcontrollers via rs489. Using the IC MAX3088, and a 100 ohm >>> resistor across A and B.. Since there are 19 MAX3088, there are also >>> 19 100 ohm in parallel. IS there something wrong with this? the >>> resulting resistance is only about 5.3 ohms. >>> rs485 has a lot better noise immunity and only needs 2 or 3 wires(+power). see http://www.circuitcellar.com/library/ccofeature/perrin0799/c79bp3.htm With the latest transceivers can run at up to 16Mb on short range (10 - 50m) or at 100Kbps or slower for up to a few km. Over 1km/4000ft you may need to insert repeaters in the line. A project I was working on and may be again (I find out tomorrow) is a bridge vibration monitoring system. We can connect all the sensor boards(4 - 8) via rs485 in each string with a single cable - 6 core twisted shielded cable. Looking at using around 100kbps per string approx 64 or 120 feet long. Usually avoid using maxim parts because they can be quite hard to get in the quantities you want at decent pricing but for rs485 they are the best! http://www.maxim-ic.com/quick_view2.cfm/qv_pk/4631 The max13088 which he is using allows up to 16Mbps(10 - 30m) and up to 256 transceivers on the bus. Nice thing is they are still available in dip. http://www.maxim-ic.com/appnotes.cfm/appnote_number/2116 Could also use can bus for longer distance comms where you can't use ethernet. The new airbus and beoing aircraft even use can over tcpip for flight controls and enginer controls. arinc 629 , 664 if you want more details. http://www.aviationtoday.com/av/categories/military/1198.html Alex