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Thread: Teensy 4 round pads, where do they go?

  1. #1

    Teensy 4 round pads, where do they go?

    The back side of the Teensy 4 has several round pads that are not labeled on the schematic or the color pin drawing. There are 4 such pads between the rectangular pads for "pins" 24-33, another one just to the right side of pads 27 and 29, and two more near the USB host pads and pads 34-39. What are these for? I am guessing that three of them are for an SWD debugger, but this is not seen on the schematic.

  2. #2
    Senior Member+ KurtE's Avatar
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    I think there is more details in the beta thread, but most of them are test points, which are used to test boards. Many are to different voltages, which are used internal to board. If I remember correctly only one might be interesting in that you might get one extra io pin...

  3. #3
    Senior Member PaulStoffregen's Avatar
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    Quote Originally Posted by scharkalvin View Post
    The back side of the Teensy 4 has several round pads that are not labeled on the schematic
    The test points are indeed shown on the schematic.

    Click image for larger version. 

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    Most of them connect to the chip's many power supply voltages. During testing, a bed-of-nails test fixture measures the voltages at all those points. It also uses them to quickly discharge every capacitor, so the board can be rapidly power cycled to perform testing of the power & ground pins.

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