I have the software, but in this existing system can only come up with 2 outputs and 1 programmable input/output (3.3V logic).
Is it OK to tie DO and DI of the SD card together via a resistor?
As far as I can see data output appears after the neg edge of the clock, and input data is sampled at pos edge of the clock, so I could switch direction on my input line?
So you get this:
SYSTEM CARD
out1 ------------------------------------ Chip select out2 ------------------------------------ Clock -------------------- DI | programmabe IO ------------- R ---------- DO
Sequence:
CS low IO pin to input clock high // sample card DO read DO IO pin to output data to output clock low // sample data on DI to card
Only drawback I can see is that data on DI will change when clock is high, but according to the specs I found this is OK after enough delay.
Anybody done this?