SanDisk SD Card

Host Design Considerations:Application NoteNAND MMC and SD-based Products Revision 1.0Table 2.MultiMediaCard and SD Card Clock Speed and Burst RateProductMaximum Clock Speed and Burst RateMultiMediaCard Clock Speed Burst RateSPI Bus mode 20 MHz 2.5 MB/sMMC 1-bit mode 20 MHz 2.5 MB/sSD CardSPI Bus mode 25 MHz 3.125 MB/sSD 1-bit mode 25 MHz 3.125 MB/sSD 4-bit mode 25 MHz 12.5 MB/sThe write and read throughput rates of the SD Card and MultiMediaCard are slower thanthe burst rate because each card includes the busy time to write data from the card’sbuffers to its internal Flash RAM, and busy time to read data from the internal FlashRAM to the card’s buffer. Since most designs use this write and read busy time tocomplete other processes, choosing a 1- or 4-bit bus mode can have a 4x speed effect onthe time spent servicing the SD Card.The example in Table 3 shows the difference between moving 512 bytes of data to andfrom a MultiMediaCard or SD Card internal buffer using different bus modes.Table 3.MultiMediaCard and SD Card Clock Speed and Transfer TimeProduct Maximum Clock Speed and Time Req. to move 512 bytesMultiMediaCard Clock Speed TimeSPI Bus mode 20 MHz 204.8 usMMC 1-bit mode 20 MHz 204.8 usSD CardSPI Bus mode 25 MHz 163.8 usSD 1-bit mode 25 MHz 163.8 usSD 4-bit mode 25 MHz 41 us© 2002 SanDisk Corporation 5 9/30/02, Lit# 80-11-00160