Re: Article on the 8088 bus cycle

On 5/16/24 4:21 PM, BGB-Alt wrote:

Seems I was wrong about something before:
The combination of CMD0+CS is what selects SPI mode (for normal SD mode, the CS signal would not be asserted).
I was mistaken in thinking that it was the stream of FF bytes and then asserting CS near the end (say, the init procedure for the SDcard involving sending a large number of FF bytes at a fairly low speed, then sending some other commands and boosting the speed to the intended operating speed).
 

The low speed was a holdover from its previous life as the MMC card standard. (I still have a 64MB MMC card.) Which were intended to be a multi-drop solution. As such some of the signal lines were open-drain/collector so the speed was limited by the pullup resistor and parasitic capacitance.
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David Schultz