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suromenggolo
Joined: 25 Feb 2005
Posts: 107
Helped: 9
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 08 Sep 2006 9:24 RS485 Cable Installation |
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Hi.. I want to installing RS-485 cable at two floor building, from master PC to slave device each doors. look at figure *.pdf
Can i install with this is.?, Please your comment and revision..?
Thank's
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DrWhoF
Joined: 06 May 2005
Posts: 309
Helped: 9
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| 08 Sep 2006 9:46 Re: RS485 Cable Installation |
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I think you should use termination resistors on both nodes close to last slave.
DrWho
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VVV
Joined: 26 Nov 2004
Posts: 1514
Helped: 280
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| 08 Sep 2006 17:34 Re: RS485 Cable Installation |
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| Absolutely. Just use termination resistors (120Ω) at both ends of the line. That would be the right-most slaves on each floor.
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xxargs
Joined: 28 Jul 2002
Posts: 231
Helped: 44
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| 08 Sep 2006 21:21 Re: RS485 Cable Installation |
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| VVV wrote: |
| Absolutely. Just use termination resistors (120Ω) at both ends of the line. That would be the right-most slaves on each floor. |
Long 'stub' from unit to 'T'-connection is not recommendate - 2 meters seems little bit long.
Think this simular SCSI and 10-base-2 - ie, no long cable from 'T'-connection point to unit , or this can make 'strange' problems later.
newer make 'star' connection point (and stubs in different way), only daisy-chain connection between units whole way from terminator in end to terminator on other end. (your 'split' between floors is a 'starpoint' here, and can make signal reflexes and possible ruins datapackage) - again - use same rules as 'old' 10-base-2'
Use very slow datarate (< 20kbit) or very fast - If possible, not use range between 20 KHz to 100-200 KHz - all signal cable type (including CAT-5) have bit a trouble in this frequency range and needs complex source and complex terminate to working well - easiest to skip... (Why RS232 at 115200 Baud not working on long cable...)
100 - 120 Ohm terminate (depend of cable - CAT-5 uses 100 Ohm) is only valid for high speed datarate above 200 kHz (>= 400 kbit/s).
Make if possible communicate-protocol not level sensitive, only level change-sensitive (ie use 8-16 bit sync sequence before valid data in every datapackage) if you want break up RS485 line galvanic between zones via trafo.
- using optocoupler to transport logic level state all time is lot more expensive compare to using simple transformer.
test system with isolating trafo simular ethernet-trafo and long lines before setting up equipment on customer...
(all 10-base2 and 10-basT, 100-base-T use transformer between each segment to avoid later problem in time network growns and connected equipment coupled to differ power source and grounds.)
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IanP
Joined: 05 Oct 2004
Posts: 6361
Helped: 1509
Location: West Coast
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| 09 Sep 2006 2:35 Re: RS485 Cable Installation |
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This guy is trying to scare you ..
Don't worry, you have alltogether <100m of cable ..
What I would add are the biasing resistors .. see picture below ..
Regards,
IanP
BTW ..
Of course the top biasing resistor should be connected to +5V ..
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suromenggolo
Joined: 25 Feb 2005
Posts: 107
Helped: 9
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| 09 Sep 2006 2:48 Re: RS485 Cable Installation |
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I think it is differenct from theory of RS485 cable installation cable, but for efficiency and building condition, RS485 cable installation must be same as it.
from master PC with RS232 --> RS485 converter --> cable --> 'T' cable to 1st floor (30m) and 2nd floor (30m). each floor cable have T cable to slave (2m).
Please your comment and revision..?
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IanP
Joined: 05 Oct 2004
Posts: 6361
Helped: 1509
Location: West Coast
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| 09 Sep 2006 3:21 Re: RS485 Cable Installation |
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Network topologies such as the star or tree are not recommended by the standard, however, it doesn't mean that your network consisting of a few slaves and less than 100m of cable won't work ..
IT WILL !!!
If the signals on the network are slow, the bit edges are long, and the cable runs are short, topology is not an issue.
Just bear in mind what has been said about termination(s) and biasing and you will be OK ..
"The Practical Limits of RS-485"
http://www.dmx512-online.com/ddloads/RS485.pdf
Regards,
IanP
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suromenggolo
Joined: 25 Feb 2005
Posts: 107
Helped: 9
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| 09 Sep 2006 3:58 Re: RS485 Cable Installation |
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Oke., thanks IanP.
however it is not recommended by the standard, is it my installation cable OK..?
length cable from master to slave must be < 100m, and any where 'T' cable it is no problem. what is like it..?
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IanP
Joined: 05 Oct 2004
Posts: 6361
Helped: 1509
Location: West Coast
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| 09 Sep 2006 4:22 Re: RS485 Cable Installation |
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From your drawing it doesn't look like you will be trying to achieve a bit rate of 35 mbps ..
No worries, mate, you will be OK ..
Regards,
IanP
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suromenggolo
Joined: 25 Feb 2005
Posts: 107
Helped: 9
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| 11 Sep 2006 2:02 Re: RS485 Cable Installation |
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| Oke, I transmit data with bit rate 9600 bps only, it is UART bit rate standart from PC.
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