<https://forum.pjrc.com/index.php?threads/external-usb-to-program-teensy-4-1.73835/>
<http://schema.org/articleBody>
"Hi,\nWe're currently developping a PCB to connect different peripherals to the Teensy 4.1. We tried adding external USB connectors to program the teensy without success. We've connected D+, D- and 0V but not VUSB since our teensy is already..."
<https://forum.pjrc.com/index.php?threads/external-usb-to-program-teensy-4-1.73835/#post-334144>