USB : USB Classes    USB Classes for Microcontrollers  

Remember that USB bus analyzer screen shot we showed you earlier in this tutorial that showed that a CDC class device wastes 50% of the USB bus bandwidth, even if it isnt't transferring any data at all?

Well, let's look at a side by side comparison with a HID device.

The screen shot on the left shows a HID device, made by our HIDmaker FS tool, while it is busy transferring 64,000 bytes per second.  It uses about 6% of the available USB bandwidth to do that.

The screen shot on the right shows that same CDC "fake serial port" device burning up 50% of the bus bandwidth, even though it isn't presently sending any data at all!


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