I'm using 2 USB hubs chained together to hook up my phone to the computer to do some testing stuff. How can I check if the USB signal is being good or not? I tried scoping the USB pins with the USB hubs connected and disconnected. Both cases had the Data+ pin around 500 mV, is this good? The waveform looks slightly different, with the signal with the hubs connected having more spikes.
Can someone refer me to a good site that covers the USB protocol? How do you know if the signal is good enough?
EDIT: I'm using a Tektronix VM 5000 HD. What voltage range should I expect to see at the Data+ pin?