I am very curious to see how a USB signal looks like but couldn't find any related article and graph still. Is it possible to see the shapes of USB and TTL data signals by using an oscilloscope. Will they be square waves and look like very similar?
My question may sound a bit weird but I always read that USB is very complicated to understand so at least I was hoping to visualize the change in USB signal when it is converted to RS232. The graphical representations in time domain. Time vs Amplitude.
I have many questions in my mind such as: "Is USB serial data less noisy than RS232? ect."(under the same circumstances with RS232) I really want to see how both USB and TTL data looks like.
I found a nice article with waveforms of RS232 and TTL. Here seems TTL is more noisy waveform than RS232 which is converted by MAX232.
But still couldn't find about USB.
Best Answer
USB - Universal Serial Bus - Signaling (WikiPedia)
The real problem with USB is not in the physical signalling. Say you capture a waveform with a scope right after the device is connected. It's likely to be a part of a Setup packet which is a part of a control transfer which is a part of a descriptor request which is a part of device enumeration, and that's only to have your device recognized by the host. Actual data transfer hasn't even started yet, and it will be wrapped inside transfers (of 4 different kinds) to some endpoint belonging to some interface that implements some device class, standard one like HID or completely custom. It's a lot like trying to understand HTTP by looking at Ethernet signal with a scope. In fact, you'd probably have a hard time finding your UART data even in a USB sniffer log (unlike a TCP/IP sniffer, a USB sniffer may well not know the exact protocol that e.g. FTDI uses to transfer data).
Together with the great USB in a Nutshell tutorial (HTML version), I found this book to be an excellent reference if you actually want working knowledge of USB to e.g. create your own USB devices.