Hardware Reference
In-Depth Information
Table 8-1. SD Card Capabilities
Standard
Description
Greater Than
Up To
Data Bus
SDSC
Standard capacity
0
2 GB
1-bit
SDHC
High capacity
2 GB
32 GB
4-bit
SDXC
Extended capacity
32 GB
2 TB
4-bit
Transfer Modes
There are three basic data transfer modes used by SD cards: 18
SPI Bus mode
1-bit SD mode
4-bit SD mode
SPI Bus Mode
The SPI Bus mode is used mainly by consumer electronics using small microcontrollers
supporting the SPI bus. Examining Table 8-2 reveals that data is transmitted 1 bit at a time
in this mode (pin 2 or 7).
Table 8-2. SPI Bus Mode
Pin
Name
I/O
Logic
Description
SPI
1
nCS
I
PP
Card select (negative true)
CS
2
DI
I
PP
Data in
MOSI
3
VSS
S
S
Ground
4
VDD
S
S
Power
5
CLK
I
PP
Clock
SCLK
6
VSS
S
S
Ground
7
DO
O
PP
Data out
MISO
8
NC
Memory cards
nIRQ
O
OD
Interrupt on SDIO cards
9
NC
Not connected
 
 
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