I made a schematic for the above mentioned board as I could not find one on the internet.
I purchased this combo board (SD + RTC) in hopes of it having the ability to tri-state the MISO when the chip was not selected. Alas this board did not tri-state the MISO.
However since I reverse engineered the schematic I wanted to post it so others could see how it can be used.
It appears the MISO line goes directly from the SD holder to pin 3 of the big header. So the card itself should go tristate on that line when it is not selected. Many microSD card modules run MISO through the 74HC125, which is wrong. But your schematic shows it wired correctly. Did it come that way, or have you modified it to make it work?
If MISO goes thru a '125 gate with it's OE/ driven by the SD CS/ line, that keeps the SD card from corrupting the MISO bus when the card is not selected. I do that on my card and it works as a very good solution.
It also keeps 5V devices from putting 5V on the 3.3V SD card MISO output line.
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