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RS485 to RS232 wiring

Created by: Per Olof at: 6/14/2010 2:36 PM (8 Replies)

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6/14/2010 2:36 PM	Rate (0)
Per Olof Posts: 311 Rating: (3)	Hello all, I have got a technical description of a transmitter and I have a question to all of you. The instrument has RS485 out and they suggest that I connect as follows to the RS232 communication module for S7-1200. I can not find any information of any connection like this on the internet, will it work ? BR Olof (Transmitter) (RS232 communication module) Instrument Pin Line 1 CDRS RS485 - ------------------- 2 RXD 3 TXD 4 DTR ----- RS485 + ------------------- 5 GND \| 6 DSR------ 7 RTS------ \| 8 CTS------ 9 RING
Per Olof Posts: 311 Rating: (3)	Last edited by: Per Olof at: 6/14/2010 2:42 PM Last edited by: Per Olof at: 6/14/2010 2:42 PM Last edited by: Per Olof at: 6/14/2010 2:41 PM Last edited by: Per Olof at: 6/14/2010 2:38 PM Last edited by: Per Olof at: 6/14/2010 2:37 PM
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6/14/2010 2:43 PM	Rate (0)
Darius Platinum Member Joined: 9/28/2005 Last visit: 3/15/2025 Posts: 2957 Rating: (243)	Hello, Its not possible to directly connect RS485 with RS232. It is physically different systems. Only way is to use signal converters. For example you can use Moxa or Advantech converters. Look at their site for more info or google "RS485 to RS232 converter". You should find some converters that suits your needs.
	Best regards, Darius
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6/14/2010 2:44 PM	Rate (0)
Kaulquappe Posts: 3093 Rating: (324)	Hello Per Olof, it won't work, when you connect RS485 directly to RS232. You need a RS485 <-> RS232 converter. I have got good experience with a W&T converter. Regards, Kaulquappe
Kaulquappe Posts: 3093 Rating: (324)	Last edited by: Kaulquappe at: 6/14/2010 2:45 PM
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6/14/2010 3:02 PM	Rate (0)
umencho Diamond Expert Joined: 3/21/2006 Last visit: 3/14/2025 Posts: 10239 Rating: (1183)	Per Olof ... and they suggest that I connect as follows to the RS232 communication module for S7-1200. ... Just to mention - is also possible to make "homemade converter". Just search into GOOGLE (example - http://pinouts.ru/Converters/rs485_cable_pinout.shtml). Best regards, Hristo Mihalev

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6/14/2010 3:55 PM	Rate (0)
Darius Platinum Member Joined: 9/28/2005 Last visit: 3/15/2025 Posts: 2957 Rating: (243)	UMENCHO Just to mention - is also possible to make "homemade converter". Just search into GOOGLE (example - http://pinouts.ru/Converters/rs485_cable_pinout.shtml). Do you think it is good idea ? I think too much pain for user. Why ? 1. Complicated to make 2. Unreliable 3. Not industrial design (rail mount, IP protection etc.) 4. Unusable in critical points 5. Stability depends on quality of welding nd used components 6. etc Not recomended, unless for personal use. Brand named converters aren't so expensive for what you get.
	Best regards, Darius
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6/14/2010 4:53 PM	Rate (0)
smiffy Platinum Expert Joined: 1/17/2007 Last visit: 3/10/2025 Posts: 1557 Rating: (540)	B+B electronics do some very nice port powered convertors that use the RS232 signals to power the device and need no separate power supply. I have used them in the past and they are very good indeed. Click here!
	Programming today is the race between software engineers building bigger and better idiot proof programs, and the universe producing bigger and better idiots. So far, the universe is winning...
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8/6/2010 3:11 PM	Rate (0)
MrPaiva Silver Member Joined: 6/29/2010 Last visit: 10/27/2022 Posts: 112 Rating: (63)	Hi to all The S7 1200 has a RS485 module: https://www.automation.siemens.com/mcms/programmable-logic-controller/en/simatic-s7-controller/s7-1200/communication/Pages/Default.aspx It is more easy use the RS485 module directly than use a RS232 module, isn't it?

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8/6/2010 4:51 PM	Rate (0)
J_Bell Posts: 5822 Rating: (412)	Hello... ... you are absolutely right, but the S7-1200 has, in difference to the S7-200, no Freeport or RS 232-Port on the CPU. So you would have to use a RS232 or / and a RS485 interface anyway. But your question was if the interfacing of RS485 to RS232 works the way you showed... and it does not. So the question was answered right, don't you think? Best regards J_Bell
J_Bell Posts: 5822 Rating: (412)
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8/6/2010 8:14 PM	Rate (0)
MrPaiva Silver Member Joined: 6/29/2010 Last visit: 10/27/2022 Posts: 112 Rating: (63)	Hi Yes, the question was answered, but I thought than maybe Mr Per Olof didn't know about the RS485 module option. Thanks.

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This contribution was helpful to 1 thankful Users J_Bell

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