The STM32F103VC microcontroller has microSD hardware built in (SDIO in the datasheet). Looking at those pins, it’s apparent that they are too deeply buried by the current design.
According to the datasheet and the DSO Quad v2.6 schematic, the pins are: (LQFP100 package)
SDIO_CMD - pin 83 (PD2) - Vusb (input from 11K/(11K+11K) voltage divider, R49 and R48, to measure Vusb)
SDIO_CK - pin 80 (PC12) - K6 (K1-K10 are key inputs from the buttons)
SDIO_D0 - pin 65 (PC8) - K3
SDIO_D1 - pin 66 (PC9) - K4
SDIO_D2 - pin 78 (PC10) - K2
SDIO_D3 - pin 79 (PC11) - K7
SDIO_D4 - pin 95 (PB8) - CHRG (input signal from U14 LTC4054)
SDIO_D5 - pin 96 (PB9) - Ax1 (controls input stage scaling)
SDIO_D6 - pin 63 (PC6) - BL (drives backlight by controlling U10 QX5239B enable - EN)
SDIO_D7 - pin 64 (PC7) - BZ (drives Q1 to control the speaker buzzer)
It’s really too bad, since there are at least 20 unused I/O pins on the FPGA that could have handled these misc I/O functions. Surely it could have been designed so that these pins were available for a microSD slot – but the current design really blocks me from rerouting these signals where I want them.
I don’t know if I’ll ever have the time, but a mini DSO like this needs a lot of work. It needs a re-worked front end. It needs a more powerful microcontroller. And it needs more than 2 MB of disk space – it really needs that microSD slot so the user has more control over storage. (I’d keep the SPI flash for firmware updates.)
Bad as it is, I’m sticking around to see if the source code shows up, but time is running out in my opinion. I don’t resent that I bought two of these units, because they’re fun toys, but I still want a “real” scope in such a portable package and will buy one if I can find one.