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???
11/22/05 17:24
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 		 #104010 - may be dangerous
Responding to: ???'s previous message
hi,

Tony Gelonese said:
2. Connect all RX pins of the micro-controllers together and all TX pins together with suitable pull-ups.


Well, with "classic" 8051 TX pin has only weak pullup internally connected during inactive state (logic high output). But who knows about other derivatives? Some derivatives (for example, SiLabs) have strong push/pull FETs at output as well. I have no idea about do they use strong pullup or weak pullup for pins utilized for alternative function (here: UART) during inactive state (for high level output). In case they do use strong pullup for TX pin, it is dangerous to connect TX pins of some MCUs together due short circuit during transmit.

Regards,
Oleg

List of 55 messages in thread
TopicAuthorDate
Home System            01/01/70 00:00      
   X10 ?            01/01/70 00:00      
   1-Wire?            01/01/70 00:00      
      Multiprocessor communcations            01/01/70 00:00      
   home system            01/01/70 00:00      
   Another Maxim - HomePlug            01/01/70 00:00      
   Simple RS232 multidrop            01/01/70 00:00      
      a dangerous approach            01/01/70 00:00      
         NOT dangerous if you read properly            01/01/70 00:00      
            So it's NOT RS232, then            01/01/70 00:00      
               Ohhh No! ..... Not RS232?            01/01/70 00:00      
                  That you get by with violating the stand            01/01/70 00:00      
                     To RS232 or not to RS232            01/01/70 00:00      
                        well, now you have both            01/01/70 00:00      
                  No Trick            01/01/70 00:00      
                  That's what I said!            01/01/70 00:00      
            dont take it personally            01/01/70 00:00      
               I won't            01/01/70 00:00      
                  on reliability etc.            01/01/70 00:00      
                     true, but...            01/01/70 00:00      
                        time is $$$            01/01/70 00:00      
                           Not bible!            01/01/70 00:00      
                        "bible" - Read, not memorise!            01/01/70 00:00      
                        Jeff, grow some skin!            01/01/70 00:00      
                        Paid help            01/01/70 00:00      
                           I agree            01/01/70 00:00      
                              Oh I am grateful            01/01/70 00:00      
               Indeed            01/01/70 00:00      
                  If this is a "put down" then I must need            01/01/70 00:00      
                     Blah blah blah            01/01/70 00:00      
                        flamewars, episode 3            01/01/70 00:00      
                  Toys !            01/01/70 00:00      
                     slobodan            01/01/70 00:00      
                        Arrogance            01/01/70 00:00      
                           totally misunderstood            01/01/70 00:00      
                              It's here            01/01/70 00:00      
                                 sorry, I do not have ESP            01/01/70 00:00      
                                    How would that help?            01/01/70 00:00      
      Long distances            01/01/70 00:00      
      Questions about your Multi MPU comm.            01/01/70 00:00      
         UART Mode 3            01/01/70 00:00      
            Re: El-cheapo home network            01/01/70 00:00      
               as dangerous and noise prone as the othe            01/01/70 00:00      
                  not "open air"            01/01/70 00:00      
                     well, I missed that, sorry            01/01/70 00:00      
                     ring protection            01/01/70 00:00      
         More info M.I.N.E.S.T.O.N.Y. Comms :-)            01/01/70 00:00      
      You must lead a very quiet life            01/01/70 00:00      
         Don't get personal            01/01/70 00:00      
      may be dangerous            01/01/70 00:00      
         RS485            01/01/70 00:00      
            RS485 addendum            01/01/70 00:00      
               RS485 only specifies the media            01/01/70 00:00      
                  Multiprocessor Mode            01/01/70 00:00      
                     comments/clrafications            01/01/70 00:00      

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