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USB OTG on FRDM-K22F? (Do I really need it?)

Question asked by David Pfaltzgraff on Nov 18, 2015
Latest reply on Dec 1, 2015 by David Pfaltzgraff

This question may be more for clarification (education on my part), but it may be an appropriate question for this forum.


I have used both the host mode (to drive a USB thumb drive) and the peripheral mode (as a USB CDC to a PC) on the FRDM-K22F, so I know that the hardware can handle it. Now, I'm running into an application where the end user would like to be able to operate in either mode according to the situation. The device just sits and collects data. Most of the time, 99%, the data is stored internally in EEPROM and then transferred to the PC via a serial link, either USB CDC or Bluetooth. However, on a rare occasion, the 1%, the device will collect more data than can be held in the internal EEPROM. What the user wants now is to be able to plug in a USB thumb drive to hold the data. When the collection process is complete, the USB thumb drive will be transfered to the PC - no need for a serial link. That's the background.


When I was approached about this, I thought, "OK. We're going to need USB OTG." But, as I get into it and found that there is no OTG demo for the FRDM-K22F, my thought it that maybe I don't need the full OTG. I just need to be able to switch modes according to user input.


First question: Any thoughts from others in the community? Am I reading this right that I can switch modes and don't need full OTG capability?


Second question: The platform is running MQX with the KSDK. Any pointers on switching modes? (Please remember that I've only used the host and peripheral modes separately.)


Final question - for now: If I really do need the full OTG capability, where can I find schematics for the hardware to support it? (I'm presuming that there's something missing in the FRDM-K22F design that precludes implementing full OTG as it is present in the TWRK22F case.)