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Thread: Teensy 3.5 working happily with RS485 transceivers at a baud of 9M

  1. #1

    Teensy 3.5 working happily with RS485 transceivers at a baud of 9M

    Hi everyone.

    I just thought I'd share this result so that anyone else who is looking for a proven Teensy / RS485 combination operating at a fairly high baud would have this as a starting / comparison point.

    I'm using 2 x Teensy 3.5 (code is compiled with CPU speed of 144MHz - that's important: quick rule of thumb, 16Mhz of CPU speed per 1Mbps serial speed, though note, it's not a law).

    They are communicating over their respective Serial 1 ports (the choice of ports can matter) at a configured baud of 9000000 (9M) with Intersil RS485 (ISL32498E) transceivers (half duplex).

    The two end points are connected by approximately 90m of cat7a (22AWG, S/FTP) cable terminated with 100 Ohm resistors. Note, cable is very important in RS485 networks. What I'm using is not RS485 recommended as it's characteristic impedance is 100 Ohm rather than 120 Ohm but as it's well shielded, the same gauge wire and a fraction of the price of your typical Belden RS485 cable. It's worth your consideration if your environment is not pushing the limits. Why 90m of cable? That's all I have! If I had more cable I'd do some testing to find distance limits at different bauds but as my production setup will be at a lower baud and a shorter distance and with different (and more expensive) cable, I can't justify the expense.

    My performance testing programs are a simple client <-> echo server type arrangement, communicating with fully stuffed 128 byte frames (the buffer for Serial1 was modified in the core files to be = 128). The client checks what is returned from the server for any corruption.

    Performance has been flawless (billions of frames sent back and forth in testing without a single error).

    I'm not affiliated with Intersil in any way and I sure haven't tried all the many different RS485 transceivers available on the market but I've spent many hours combing through datasheets and then buying promising looking transceivers to test and these are hands-down my favourites. They have a bunch of extra features which can save your sanity (high transient over-voltage tolerance; fault protection of the bus pins; high ESD protection; full fail-safe and hot plug abilities). They also exceed many of the fundamental RS485 transceiver specs (greater VOD, greater CMR, 1/4 unit load etc).

    Good luck with your Teensy / RS485 projects. When I finish my humble little RS485 Master/Slave library I'll post it. If anybody wants a copy of the basic performance testing programs referred to above just let me know (but just so you know, they're a bit rough

  2. #2
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    Iím always interested in seeing how people code something iíve done .
    Paste it here, no judgement I promise

    Or pm.(if that exists here?)

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