Teensy 3.1 USB and Bootloader without USB Cable

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afterhoursengineering

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My goal is to use the Teensy 3.1 as part of a larger circuit and the USB cable will not be plugged in to the Teensy itself. Rather, I'll have pogo pins connecting to the USB + and USB - pins for USB communication and bootloading. What I don't know is how to connect USB pin 4 from the micro-USB connector. Do I need pin 4 for anything? Is it required for bootloading or entering bootloader? There is a connection from USB pin 4 to the Mini54Tan (P0.0 pin 26) but I don't know what it does or how I should connect it.

Anyone have experience with this pin or know what it's for?
 
It's confusing to me, but pin 4 is not needed. If memory serves, it has to do with USB host mode and two smart USB devices negotiating who will be master and who will be slave.

Your average USB-A connector only has 4 pins, so nothing is attached to pin 4 of a Mini B connector when the other end of a cable is a USB-A connector. You don't need it, I have left that pin grounded in the past.
 
afterhoursengineering said:
Do I need pin 4 for anything?
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No, it's not really needed.

In a distant possible future, where we have really good USB host library support AND a new version of the bootloader supports some sort of non-USB way to get your code into Teensy, that pin will be used to signal the USB is running in host mode. But even then, it probably won't be used. In all likelihood, a special cable with only 4 wires, from the Micro-B to a standard USB-A female (same as on your PC) would be used in nearly all cases. True USB OTG products, that can recognize that pin and switch modes, are very rare. So are USB cables that bring that signal through.

So it's not needed, and even when/if it ever could be, it probably won't be needed even then.
 
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