Host Design Considerations:
Application Note
NAND MMC and SD-based Products
Revision 1.0
© 2002 SanDisk Corporation
5
9/30/02, Lit# 80-11-00160
Table 2.
MultiMediaCard and SD Card Clock Speed and Burst Rate
Product
Maximum Clock Speed and Burst Rate
MultiMediaCard
Clock Speed
Burst Rate
SPI Bus mode
20 MHz
2.5 MB/s
MMC 1-bit mode
20 MHz
2.5 MB/s
SD Card
SPI Bus mode
25 MHz
3.125 MB/s
SD 1-bit mode
25 MHz
3.125 MB/s
SD 4-bit mode
25 MHz
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
Maximum Clock Speed and Time Req. to move 512 bytes
MultiMediaCard Clock
Speed
Time
SPI Bus mode
20 MHz
204.8 us
MMC 1-bit mode
20 MHz
204.8 us
SD Card
SPI Bus mode
25 MHz
163.8 us
SD 1-bit mode
25 MHz
163.8 us
SD 4-bit mode
25 MHz
41 us