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   PID: SoupGate-Win32 v1.05   
   On 2024-01-05, 56g.1183 <56g.1183@ztq4.net> wrote:   
   > On 1/4/24 7:27 AM, Jim Jackson wrote:   
   >> On 2024-01-04, 56g.1183 <56g.1183@ztq4.net> wrote:   
   >>>>   
   >>>> Pis can do *serial* directly, but not RS232.  They only have 3.3V signal   
   >>>> levels, so voltage conversion needed for RS232 or another voltage (1.8V,   
   5V,   
   >>>> etc).   
   >>>   
   >>>     Yep ... level-shifting chips are generally needed.   
   >>>     The MAX3232 will do it.   
   >>   
   >> It does more than "level shift" it also inverts the signals. It will   
   >> accept 3v or 5v logic, even though supplied from a 3.3v supply.   
   >   
   >   
   >    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.   
      
   >    There IS still some equipment that expects   
   >    those kinds of signals ... albeit mostly early-80s. Some industrial   
   >    controllers of that vintage are still in use however.   
   >   
   >    Flow-control ... sticky. For RECEIVING no modern cpu/controller   
   >    is so slow that it cannot absorb such comms at even the highest   
   >    usual RS232 speeds. However those ancient devices you may be   
   >    communicating with may NOT be able to absorb the info so quickly.   
   >    Ergo you have to respect their flow-control lines. Serial comms   
   >    can be a pain in the ass. There are subtle issues.   
   >>>   
   >>> https://www.analog.com/media/en/technical-documentation/data   
   sheets/MAX3222-MAX3241.pdf   
   >>>   
   >>>     If you are talking to VERY old serial devices that still   
   >>>     expect some plus/minus 12v or more signals then you may   
   >>>     have to double-up, add a MAX232 after the 3232   
   >>   
   >> Maybe. But not as you say. You would need a simple 3v to 5v level   
   >> shifter (so as NOT to invert the signal) then the MAX232.   
   >   
   >    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.   
      
   --- SoupGate-Win32 v1.05   
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