[Mark1960]

I didn’t include slow clock as it doesn’t seem to be needed for most cards.

Chip select is driven from 74HCT175 via schottky diodes so no level shift needed. The pull up within the micro sd card can be used as a card presence detect, though the sockets I’ve used also include a switch.

I did have some reliability issue at 20MHz clock speed, possibly timing between clock and data due to gate delays. I didn’t have a scope to investigate in detail, and still haven’t got round to trying to improve this now that I have a scope as it works fine at 18MHz.