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Lukas Valecky
08/03/11 06:45
Read: 1439 times
Jablonec Nad Nisou
Czech Republic

#183174 - Problem with RS232/RS485 converter...
Hello all,

I would like to ask you for your help. I have a system composed of a computer with RS232, RS232/RS485 converter and several RS485 devices which can communicate at 57600bps with each other and with the computer as well. Everything works correctly until I disconnect the converter from the computer (the converter is still powered). It makes the devices unable to communicate among each other and this is the problem. I think it is caused by interference between RXD and TXD in RS232 cable (approx 1m long) which was disconnected on the side of the computer. I found out that signal from a RS485 device converted to RXD signal for PC interferes with TXD in the cable and goes back to the converter. HC4538 takes it as a computerís transmission and set ADM485 to driver function that leads to collision. So I would like to ask you how to avoid this interference. When I put 1k ohm resistor between GND and TXD at the end of the cable it works. But I donít know if it is the right solution. Could you suggest me any other, please? I also tried to shorten the cable to 0.5m and it works as well but it is undesirable. Thank you very much for your opinion.

List of 29 messages in thread
Problem with RS232/RS485 converter...      Lukas Valecky      08/03/11 06:45      
   More info please      Per Westermark      08/03/11 07:50      
      probably      Stefan KAnev      08/03/11 12:01      
   more info...      Lukas Valecky      08/04/11 03:47      
      yes,i think      Stefan KAnev      08/04/11 05:24      
         input impedance      Lukas Valecky      08/04/11 08:41      
            i'm wrong      Stefan KAnev      08/04/11 09:07      
               what is the right value?      Lukas Valecky      08/04/11 11:18      
                  did You tryed capacitor?        Stefan KAnev      08/04/11 12:41      
                     thanks...      Lukas Valecky      08/04/11 12:53      
                     it works...!      Lukas Valecky      08/05/11 03:09      
                        congrats      Stefan KAnev      08/05/11 03:20      
                           shape      Lukas Valecky      08/05/11 04:27      
                              dont      Stefan KAnev      08/05/11 04:44      
                                 It is OK.      Lukas Valecky      08/08/11 03:08      
   Hints...      Kai Klaas      08/05/11 12:34      
      schema      Lukas Valecky      08/08/11 02:57      
         Repair...      Kai Klaas      08/09/11 12:06      
            transils...      Lukas Valecky      08/11/11 08:03      
               RS485      Michael Karas      08/11/11 08:59      
                  Sample Schematic      Michael Karas      08/11/11 14:14      
                     Thank you very much for the schema...      Lukas Valecky      08/16/11 06:15      
               AVX varistors...      Kai Klaas      08/12/11 06:31      
                  capacitor      Lukas Valecky      08/16/11 07:00      
                     capacitors...      Kai Klaas      08/16/11 09:18      
                        GNDs      Lukas Valecky      08/17/11 02:21      
                           1992      Kai Klaas      08/18/11 07:08      
                              Thanks...      Lukas Valecky      08/19/11 09:10      
                                 Links...      Kai Klaas      08/19/11 15:21      

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