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   REPLYADDR 56g.1183@ztq4.net   
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   MSGID:  7b925cfc   
   REPLY:  ff3073e3   
   PID: SoupGate-Win32 v1.05   
   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. 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-   
   heets/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.   
      
   >> ...snip...   
   >>     Anyhow, peruse the usual spots, AdaFruit, SparkFun,   
   >>     Seeed. They may have a canned solution.   
   >   
   > sound advice.   
      
      These days there's often a canned fix for just a few dollars.   
      Kinda takes the fun out of it though  :-)   
      
   --- SoupGate-Win32 v1.05   
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