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Thread: Teensy 3.2 USB ID Pin 4 functionality question.

  1. #1
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    Teensy 3.2 USB ID Pin 4 functionality question.

    Hey I'm designing a board based on the Teensy 3.2 reference design. I was hoping to switch from the micro-USB connector to USB type A to just have a less flimsy connector. I noticed pin 4 (the ID or sometimes N/C pin) is connected to both the bootloader and the NXP chip.

    My question is does it serve any specific function for the Teensy 3.2 or can I safely remove it from my design?

    Thanks

  2. #2
    Senior Member+ Frank B's Avatar
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    Quote Originally Posted by tadzio93 View Post
    Hey I'm designing a board based on the Teensy 3.2 reference design. I was hoping to switch from the micro-USB connector to USB type A to just have a less flimsy connector. I noticed pin 4 (the ID or sometimes N/C pin) is connected to both the bootloader and the NXP chip.

    My question is does it serve any specific function for the Teensy 3.2 or can I safely remove it from my design?

    Thanks
    I don't think Paul made this connection out of boredom, or because he had too much room on the pcb he wanted to fill.
    I guess it has a function. Perhaps for a planned USB-Host functionality?

  3. #3
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    Yea I assumed it had some purpose. I don't plan on using it as a host. Just looking to program the board over USB, provide power, and possibly send serial data over USB as a slave.

  4. #4
    Senior Member PaulStoffregen's Avatar
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    Short answer: you can leave that wire out. It's not used and never will be.

    Long ago, like in mid-2012, I imagined someday supporting USB host on Teensy 3.0. If you look at the 3.0 schematic, you'll see I connected the I2C signals (pins 18 & 19) also to the bootloader chip. The idea that never was implemented and never will be, envisioned using a 2nd Teensy 3.0 which would talk to the bootloader chip over I2C. The theory was the 2nd Teensy could communicate with Teensy Loader on your PC and cause the bootloader on the 1st board connected as a USB host (therefore not connected to your PC at all) to load new code.

    That crazy idea was never implemented and never will be. Those I2C connections were dropped in the change from Teensy 3.1 to 3.2, which also switching from Nuvoton MINI54 to Freescale MKL02 (which didn't exist in 2012). Now we support USB host on Teensy 3.6 and 4.0, with the 2nd USB port.

    So the USB port is always used only in device mode. That wire is a left-over from the Teensy 3.0 & 3.1 days. It is never used and never will be used. It has been removed on the all the newer boards.

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