V-USB states that "devices based on V-USB cannot comply to the electrical specifications of the USB standard because the AVR's I/O characteristics don't match the requirements of USB".
Can someone elaborate on this? What specific characteristics of AVR's does the USB certification not agree with? I'm trying to understand why it seems like the only way to make a USB-compliant device is to use a much more powerful MCU with built-in USB communication (I'm currently using the ATTiny series) or one of those expensive FTDI interface chips.
V-USB certification non-compliance details
Re: V-USB certification non-compliance details
I think at the very least it doesn't do differential reception, where the voltages of the two data lines are compared (which increases noise immunity). I also don't think the CRC of packets is checked and errors reported to the host so it can re-send transparently.
