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

  1. #1
    Senior Member
    Join Date
    Jun 2017

    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 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?



  2. #2
    Senior Member
    Join Date
    Apr 2014
    These are the alternative pins.
    i.e. if you want to use Serial1, and pins 26, 27 instead of 0,1

    You would use

    This is decribed here:
    ...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
    Join Date
    Jun 2017
    Thanks! I love it when someone knowledgeable explains how the magic works!

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