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01/20/09 21:09
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  01/20/09 21:09
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 		 #161661 - RS-232 transceiver in PC
Responding to: ???'s previous message
Stefan Kanev said:
P.S. I did never see clean MAX232 on mother board.

Most probably there is none. The vast majority of RS-232 transceivers on motherboards with built-in COM port is GD75232 or its derivative. It's a 3-output 5-input transceiver (i.e. one chip is enough for all signals on one COM connector - you would need 3 MAX232-s for that), working out of a positive and a negative power supply (+12V and -12V), i.e. it does not have the charge pump. Note, that ALL desktop-class PCs have -12V supply, and last 15 years the RS-232 transceiver is the sole reason for it.

Exemption from this are laptops, where a 3/5 transceiver WITH pump is the norm. This is why they have usually lower output voltage (said +-8V or so - the standard requires +-3V so that's still within the limits), and also significantly lower loadability.

JW


List of 34 messages in thread
TopicAuthorDate
Serial Communication Problems            01/01/70 00:00      
   standards have a purpose            01/01/70 00:00      
      Serial Communication Problem            01/01/70 00:00      
         OH, how often            01/01/70 00:00      
   No negative Tx supply            01/01/70 00:00      
      Serial Communication Problem            01/01/70 00:00      
   Software or documentation bug            01/01/70 00:00      
      I am so new sorry            01/01/70 00:00      
         Reset            01/01/70 00:00      
   I found this Image at google            01/01/70 00:00      
      Read datasheets to better understand            01/01/70 00:00      
      which derivative            01/01/70 00:00      
      It will meet the RS232 requirements            01/01/70 00:00      
         Are You sure?            01/01/70 00:00      
            are you saying "PC" when you say "mother board"            01/01/70 00:00      
               You are right , Eric,            01/01/70 00:00      
                  because            01/01/70 00:00      
                     cheap is paradigm today, so            01/01/70 00:00      
                        That's odd ... I've never seen one ...            01/01/70 00:00      
                           odd, but real .            01/01/70 00:00      
                              Explaining to beginners            01/01/70 00:00      
                                 agree            01/01/70 00:00      
                           look for a copy of the EIA standard and read it            01/01/70 00:00      
                           right, but not the issue            01/01/70 00:00      
            RS-232 transceiver in PC            01/01/70 00:00      
   Basics            01/01/70 00:00      
      MAX232 vs DS275            01/01/70 00:00      
         It is not that simple            01/01/70 00:00      
            I bought the required componentss            01/01/70 00:00      
               It worked! Yahoo!!!!Googlooo!!!            01/01/70 00:00      
   Circuit Design            01/01/70 00:00      
      May need to have pullup resistors            01/01/70 00:00      
         It worked, thanks!            01/01/70 00:00      
            It destroyed though my red led            01/01/70 00:00      

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