<https://lh3.googleusercontent.com/-rQyASn6leVw/V1MMSe6FcqI/AAAAAAAAACQ/nGU2rVNEvq8ucKuNZs0APRIeGQFc5WQjgCLcB/s1600/26J50_USB-circuit.jpg>
Both the USB and serial header Vcc go to a MIC5219 3.3V regulator. When
both are plugged-in it is essentially the same 5V from the PC USB poewr
bus, that's why it's a non-issue. The attached circuit was a testbed
design, I just chucked-on the 18F26J50/SD circuit as a way to test the SD
functionality, specifically with the C18 libraries.
In any case, when you power via the serial header the circuit appears to
act normally, listing the contents of the SD card in the terminal window.
If you then plug-in the USB connection, the terminal window indicates that
("USB connected") and you get the expected little "dots" being output to
the terminal after the USB connected message.
When you power via USB, with *either *the serial/external power present or
not, the result is the same, the Mass Storage Device is detected, but the
"drive" itself can never be mounted.
Something not quite right with the code. Very close probably, but no idea
where the issue lies... As I mentioned before, the result was the same on
a completely different DIP MCU board design
On Saturday, June 4, 2016 at 1:49:36 AM UTC-4, Matthew Schinkel wrote:
>
> - When externally powered the SD card is recognized and the directory is
> read correctly.
>
> Are you saying when you use an external power source and connect USB, the
> PC can read the card?
>
> If you are using USB to power the circuit, USB power is 5v. Do you step it
> down to 3.3v?
>
> Matt.
>
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