RS485 Troubleshooting

RPI Linux RS-485 with CH340B chip (Sometimes misses 7th byte, on specific reading)

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I have a problem with RS-485 communication. Sometimes reading misses 7th byte (so it misses start bit). It happens only on specific reading (position of elevator 529 +-2). Otherwise is communication always stable and it works fine for almost a year now. We are using RS-485 half-duplex and 19200 baud.

I’m attaching images of output of logic analyzer and readings of specific problem.

And code Editor (Visual Studio) (picture was taken with phone), everything is visible: raspberry-pirs485shareedit  follow  flag asked 21 mins agoBlaž Filipič111 bronze badge New contributor

  • 1You literally just asked the identical same thing minutes ago: electronics.stackexchange.com/questions/541996/… – Marcus Müller 14 mins ago
  • Question was deleted. – Blaž Filipič 13 mins ago
  • 1Yes, you deleted it, and then opened this new, identical one. Don’t close questions and then open identical new ones minutes later – what sense does that make? If anyone was writing an answer over there, their progress is now lost. You’re actively consuming community time with such moves! – Marcus Müller 8 mins ago
  • (1) RS-485 half-duplex 19200bd is common standard and if your application works Ok for one year, then software and hardware should be reliable. (2) What is NOT reliable is.hardware related to “position of elevator 529 +-2”. (3) If the problem is intermittent, then it is usually very difficult to troubleshoot. The usual workaround is (a) replace the related hardware (adapter and wiring connectors) with a new set and see if problem disappears. (4) Or there might be noise/glitches/flickering somewhere near Elevator 529. Just brainstorming wild guesses. Cheers. – tlfong01 8 mins ago   
  • You also need to actually ask a specific question. – Andy aka 7 mins ago
  • (5) If Elevator 529 is near a huge AC induction motor, say, then the EMI noise etc can not be practically eliminated, then you might consider doing extra parity checking for messages related to the particular elevator and resend messages. Again just brainstorming. Good luck and cheers. – tlfong01 37 secs ago   Edit   

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