I'd like to add an SD card slot to the 8-bit computer I'm building. My idea is to implement a bit-banged SPI interface, but since the CPU clock speed is so low (1MHz), the SCLK frequency will be very low; 100kHz or lower.

I know that SD cards have maximum SPI clock frequencies; do they have minimum clock frequencies? Or can the master toggle the clock line as slow as it wants to?

 

Often it's DC as it's a static clock, but always check the datasheet.

 

IIRC the clock can be kept waiting as long as you need. But the mmc and sd specification is always handy if you want to communicate with the card correctly