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Thread: Teensy 4.0 5V to 3.3V Encoder RS422 Differential Line Receiver?

  1. #1
    Junior Member
    Join Date
    Feb 2021
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    2

    Teensy 4.0 5V to 3.3V Encoder RS422 Differential Line Receiver?

    Hello,

    I have a 5V encoder that I would like to connect to the 3.3V Teensy 4. I peeked in side the encoder housing and found that it has a chip number AM26LS31C(RS422 Differential Line Driver). I googled what chip should be used for the receiver and found number AM26LS32AC(RS422 Differential Line Receiver).

    I looked at the data sheet but unfortunately I don't know how to interpret the info on it very well Does anyone have experience with these part numbers on a 3.3V Teensy 4? If the line receiver above won't work does anyone know of the correct one for the Teensy voltage range?

    Also what would be the recommend way to connect a 5V encoder to the 3.3V Teensy when just using the A and B without the /A /B and not involving a RS422 differential signal? I googled and made a voltage divider but wants sure if there was something better or not.

    Here is the link to the data sheets:
    https://www.ti.com/lit/ds/symlink/am...oogle.com%252F

    https://www.ti.com/lit/ds/symlink/am...oogle.com%252F

    Here is a picture of the encoder:
    Click image for larger version. 

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    Thank you,

  2. #2
    Senior Member
    Join Date
    Jul 2020
    Posts
    927
    A and #A form a pair, B and #B form a pair - those can be routed as twisted pairs, but twisting A with B will risk
    crosstalk between the quadrature channels.

    Each RS422 pair needs termination at the receiving end, a 120 ohm resistor is a reasonable match to CAT5 or similar cable.

    Its best to use a differential receiver (the AM26L32 available: https://uk.farnell.com/texas-instrum...97?st=am26ls32)

    For single ended output you can probably get away with a simple resistor divider as you think, using A/GND and B/GND
    as twisted pairs, again terminated with about 120 ohms and check the voltages you actually get with a meter are suitable
    for 3.3V logic - if not you'll need that receiver chip or at least a dual comparator - differential is the preferred approach.

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