I know a fair bit about USB, but for some reasons I am not able to answer this question myself.
Does the USB Host port (let's say USB 2.0) always supply 5V on the VBUS pin? If not, how does it detect device connection?
For device (bus-powered case) it is easy to detect host by sensing the VBUS pin, but for this to work USB Host should always provide 5V on the VBUS pin, which results in me asking this question.
One thing I can think of is it can provide 5V, 100mA by default, and more only after successful enumeration. But as far as I have observed, the USB ports on laptop have 5V VBUS enabled by default and not limited to 100mA, so I just want to understand from USB standard point of view.
Any reply will be much appreciated.