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   REPLYADDR jj@franjam.org.uk   
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   MSGID:  00fa7b28   
   REPLY:  1d97bd38   
   PID: SoupGate-Win32 v1.05   
   On 2024-01-08, Michael Schwingen  wrote:   
   > On 2024-01-07, Jim Jackson  wrote:   
   >>>    Properly wired, the MAX232 can deliver "real" RS-232 ... including   
   >>>    the negative voltages.   
   >>   
   >> The 3232 does provide the negative and positive voltages but only at   
   >> +/-5.5v Which is fine for most modern stuff, but as you say below not   
   >> for some older stuff.   
   >   
   > Which means the older stuff is broken and not really conforming to RS232 -   
   > the signals from the '3232 & Co *are* fully RS232-compliant.   
      
   Indeed, and as you say the blame is on the equipment - but in the late   
   80's early 90's there was a lot of crap^H^H^H^H non-conformant equipment   
   :-)   
      
   > Yes, I know broken stuff exists and if you need to interface to such stuff,   
   > you need better drivers, but the blame is on the broken equipment and not on   
   > the MAX3232.   
   >   
   >>>    Again, depends on what you are trying to converse with.   
   >>>    Very old devices may expect/depend on those rather high   
   >>>    negative signal levels.   
   >>   
   >> Indeed, which the max232 provides, +/- 12v. But it needs driving with 5v   
   >> logic levels. Hence the need for the 3v-to-5v level shifters BEFORE the   
   >> MAX232 inputs.   
   >   
   > When driving a RS232 load, the MAX232E output is specified at +-9V typical,   
   > +-5V guaranteed minimum - not +-12 (it internally doubles the +5V supply, so   
   > there is no way to get above 10V).   
      
   Ah I mis-remembered - thanks for that.   
      
   > The MAX3232 output is +-5V minimum, and +-5.5V typical.   
   >   
   > If you really need more output swing, you will have to use something like a   
   > SN75188 (with a 3.3V -> 5V level converter, and +-13V supplies) - at   
   > VCC=+-13.2V, these will drive +-9V guaranteed and +-10.5V typical.   
   >   
   > With Vih=1.9V, these might even work from a 3.3V output without additional   
   > level translation.   
   >   
      
   cheers   
      
   --- SoupGate-Win32 v1.05   
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