SanDisk SDSDH-1024 Product Manual - Page 121

Host Design Considerations: NAND MMC and SD-based Products Application Note Revision 1.0 Table 2. MultiMediaCard and SD Card Clock Speed and Burst Rate Product MultiMediaCard SPI Bus mode MMC 1-bit mode SD Card SPI Bus mode SD 1-bit mode SD 4-bit mode Maximum Clock Speed and Burst Rate Clock Speed Burst Rate 20 MHz 2.5 MB/s 20 MHz 2.5 MB/s 25 MHz 25 MHz 25 MHz 3.125 MB/s 3.125 MB/s 12.5 MB/s The write and read throughput rates of the SD Card and MultiMediaCard are slower than the burst rate because each card includes the busy time to write data from the card's buffers to its internal Flash RAM, and busy time to read data from the internal Flash RAM to the card's buffer. Since most designs use this write and read busy time to complete other processes, choosing a 1- or 4-bit bus mode can have a 4x speed effect on the time spent servicing the SD Card. The example in Table 3 shows the difference between moving 512 bytes of data to and from a MultiMediaCard or SD Card internal buffer using different bus modes. Table 3. MultiMediaCard and SD Card Clock Speed and Transfer Time Product MultiMediaCard SPI Bus mode MMC 1-bit mode SD Card SPI Bus mode SD 1-bit mode SD 4-bit mode Maximum Clock Speed and Time Req. to move 512 bytes Clock Speed Time 20 MHz 204.8 us 20 MHz 204.8 us 25 MHz 25 MHz 25 MHz 163.8 us 163.8 us 41 us © 2002 SanDisk Corporation 5 9/30/02, Lit# 80-11-00160