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   MSGID:  efd2881d   
   REPLY:  f4276dee   
   PID: SoupGate-Win32 v1.05   
   On 1/7/24 2:50 PM, Jim Jackson wrote:   
   > 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/dat   
   -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.   
      
      
      Probably true. I think the 3232 is 3.3 in/out so some kind   
      of level-converter would be required between it and the 232.   
      Cheap, or you can make yer own, but it's an extra level of   
      complication.   
      
      Thing is, some of that old equipment (oft industrial) IS still   
      out there doing its job so a Fake-to-Real RS232 (might add a   
      couple other RS's) converter might be a worthwhile bit of kit   
      to have around.   
      
      There's also the issue of the flow-control lines. While modern   
      stuff is fast enough to not worry about it, the old equipment   
      might need to signal a brief stop while you are sending to it.   
      Buffers were often very small back then (and processing slow).   
      
      Async is versatile, but a pain in the rump sometimes. Synchronous   
      serial is more civilized. However most equipment you'll ever come   
      across is async.   
      
   --- SoupGate-Win32 v1.05   
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