How is it possible that the ALFAT OEM only sends only a small voltage (under 1V) toggle to the PC over DP2 and DM2?
I’m working on a project where my custom circuitboard controls an ALFAT OEM board. My handheld device logs data to the SD card. Then when the user connects to a PC, the device switches ALFAT to sd-reader. I have one alfat on a breadboard which works perfectly. I can change modes, then connect to the PC as external storage device. My oscilloscope shows that DP2 and DM2 toggle high to 4-5V. great!
However… on my prototype circuitboard, when I send the command to initialize sd-reader mode, the DP2 & DM2 lines toggle but the voltage is very weak (under 1V).
So how did I mess up? I’m wondering if I somehow fried something on my alfat accidentally? But it can still write to the sd card ok. Originally I screwed up and had the USB data lines connected in parallel to an FT232 uart converter. That was dumb, but I removed the connecting wires. Could doing that damage the ALFAT or the FUSB2805?