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???
11/27/07 07:55
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 		 #147443 - There is a way to be sure.
Responding to: ???'s previous message
Neil Kurzman said:
1) Check his VCC 5V and the MAX232 + and - 9
2) Measure the AC Volts AC Power Supply to AC Ground It should be millivolts (ie just noise)
3) Measure the AC and DC Volts from the ground pin of his bourd to the PC Ground. Again it should be small.

An Isolator will make it work, But it will not fix the problem



The old "standard" receiver for RS232 had 3.8K ohms in series with its inputs. The old "standard" driver had 300 ohms in series with its outputs and its outputs diode clamped to the rails. A dead short to either rail, if supplied by the MAX232 wouldn't damage anything. A dead short to GND wouldn't either. Nearly every monolithic driver or receiver uses a similar strategy to ensure it performs at least as well and safely as that old driver/receiver pair.

If the MAX232 is getting hot, I think it's safe to say it's because of something on the MAX232. Disconnecting it from the MCU and the PC will settle that.

RE


List of 60 messages in thread
TopicAuthorDate
PC COM Ports Damaging !!!            01/01/70 00:00      
   Earth loops?            01/01/70 00:00      
      Why Now and this circuit ?            01/01/70 00:00      
   Damage?            01/01/70 00:00      
      I am Sure ...            01/01/70 00:00      
   Common mode            01/01/70 00:00      
      You haven't mentioned            01/01/70 00:00      
   do you have the shell of DB9 grounded?            01/01/70 00:00      
   Serial port damage            01/01/70 00:00      
      for serial port damage            01/01/70 00:00      
         No            01/01/70 00:00      
      No, that can't be right!            01/01/70 00:00      
         re:3.3V            01/01/70 00:00      
            are you sure about that, Andy?            01/01/70 00:00      
   Are You SURE?            01/01/70 00:00      
      I'm sure Dear ...            01/01/70 00:00      
         not to be argumentative ... but ...            01/01/70 00:00      
   check it            01/01/70 00:00      
      Checks            01/01/70 00:00      
         We haven't seen how the DB-9 is wired            01/01/70 00:00      
            It\'s probably not a DB-9!            01/01/70 00:00      
               sure, but            01/01/70 00:00      
               Sloppy terminology            01/01/70 00:00      
   My Burned out ports            01/01/70 00:00      
      What?            01/01/70 00:00      
         What I mean is            01/01/70 00:00      
   a common misunderstanding is            01/01/70 00:00      
      So problem is in "modern" PCs?!            01/01/70 00:00      
      So problem is in "modern" PCs?!            01/01/70 00:00      
         maybe i'm wrong            01/01/70 00:00      
   try with opto coupler and +9 volt supply            01/01/70 00:00      
      Back when folks cared whether things work ...            01/01/70 00:00      
      Assuming He does not have one            01/01/70 00:00      
         There is a way to be sure.            01/01/70 00:00      
            Standard            01/01/70 00:00      
               Power Supply ...            01/01/70 00:00      
                  Dwhatever9 shell connection to GND...            01/01/70 00:00      
                     about that shell-to-shell connection            01/01/70 00:00      
                        generally...            01/01/70 00:00      
                  Truth emerges            01/01/70 00:00      
                     developed?            01/01/70 00:00      
                  that\'s the problem!            01/01/70 00:00      
         HUH?            01/01/70 00:00      
      why??            01/01/70 00:00      
         Broken COM port suggestions            01/01/70 00:00      
            he is not wrong - if            01/01/70 00:00      
               ...he is not wrong... only said watch it            01/01/70 00:00      
                  BULL!!!            01/01/70 00:00      
                     Bull?            01/01/70 00:00      
                        yes, genuine male cow manure            01/01/70 00:00      
                           Eric, you are a sad man            01/01/70 00:00      
                           Amateurs and pros            01/01/70 00:00      
                              of course I do            01/01/70 00:00      
                     Well, it has to do...            01/01/70 00:00      
                        Kai, I now you know this stuff ... but            01/01/70 00:00      
                           Different CMOS design?            01/01/70 00:00      
   that's right, when you can not argue tha facts ...            01/01/70 00:00      
      My Dear Friends ...            01/01/70 00:00      
         look in the datasheet            01/01/70 00:00      
            Y E S . . .            01/01/70 00:00      

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