SanDisk SDSDB-016G-A11 Product Manual page 121

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