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Thread: RX/TX question on Teensy 4.0

  1. #1

    RX/TX question on Teensy 4.0

    Hi there,

    I'm working on an installation for which I need to use 3x RX/TX pins from the Teensy 4.0. Two of them go to FTDI converters that then connect to two Raspberry Pi, and one goes into an XBee RF controller.
    On the Teensy 4.0 pin-out sheet I noticed the pins at RX2 and TX2 have an IN label on the TX, and an OUT label on the RX. (Same for the TX3/RX3). I've come to understand that TX is for transmitting (OUT) and RX for receiving (IN). So what are these labels for, can I still use the TX for transmitting and the RX for receiving or should I follow the IN/OUT labels. I'm designing a little breakout in Kicad that allows me to connect everything smoothly so would like to have this right

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  2. #2
    Senior Member+ MichaelMeissner's Avatar
    Join Date
    Nov 2012
    Ayer Massachussetts
    The IN/OUT labels are for other functions. RX2 and TX2 are also used for the first I2S (sound) bus. RX3 and TX3 are also used for the S/PDIF (different sound) bus.

    If you look at the pinout card, sound pins are yellow, Serial uart pins are light blue. If you use RX2/TX2 for a uart, then you won't be able to use the first I2S bus. You could use the second I2S bus (pins 2-5 and 33) if you needed digital sound. The S/PDIF bus is present in the hardware, but I'm not sure if the library currently implements it.

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