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Thread: Teensy 3.5 pins 0,1 same as 26,27?

  1. #1
    Senior Member
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    Jun 2017
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    Teensy 3.5 pins 0,1 same as 26,27?

    I'm planning to incorporate a T 3.5 in an upcoming robot project, and I'm having a bit of trouble decoding the pin assignments diagram at https://www.pjrc.com/teensy/pinout.html. A number of pins have multiple functions, and in particular pins 0,1 and 26,27 both have RX1/TX1 assignments (along with others). I plan to use RX1/TX1 to connect to an HC-05 BT module for OTA firmware updates, and I had also planned to use pins 25/26 for general purpose digital I/O.

    I found this post which seems to indicate that I can indeed use 0,1 for TX1/RX1 and 25,26 for general purpose digital I/O because (if I have this right) TX1/RX1 shows up on EITHER pins 0,1 OR pins 25/26, but not BOTH - is that indeed correct?

    And following up on that, is the pin labelling color and font size on the pin assignment diagram intended to denote the [B]DEFAULT[B] and alternate pin assignments for a function such as TX1/RX1? So pins 0,1 are the default pins for RX1/TX1 respectively, but (with some unknown magic) could instead show up on pins 27,26 instead?

    Same thing for SDA0/SCL0? The DEFAULT pins are 18,19 respectively, but with some other magic incantation could instead show up on pins 33,34 instead?

    TIA,

    Frank

  2. #2
    Senior Member
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    These are the alternative pins.
    i.e. if you want to use Serial1, and pins 26, 27 instead of 0,1

    You would use
    Serial1.setTX(26);
    Serial1.setRX(27);

    This is decribed here: https://www.pjrc.com/teensy/td_uart.html
    ...which tells you how to use the "magic".

    And yes, if you don't want to use the alternatives, and use it i.e. for digital IO - just do that. pinMode(26, ...) and digitalWrite(26, ..) will work.
    Yes, same for SDA0/SCL0

  3. #3
    Senior Member
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    Jun 2017
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    Thanks! I love it when someone knowledgeable explains how the magic works!

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