ALFAT OEM sd-reader doesn't connect

File-System Hardware
1

Hi,

question:
How is it possible that the ALFAT OEM only sends only a small voltage (under 1V) toggle to the PC over DP2 and DM2?

background:
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?

2

you might need to show your actual PCB schematic to get more depth in responses. I’d expect that this is a more likely area you’ll hit an issue…

3

@ solara.kane -

  • Looks like there is no connection on Pin 18 where input 5V for USB?
  • Did you modified hardware on ALFAT OEM? seems to be that C1 is removed.