Cactus Technologies Limited

Suite C, 15/F, Capital Trade Center

62 Tsun Yip Street, Kwun Tong

Kowloon, Hong Kong

Tel: +852-2797-2277

Email: [email protected]

Cactus USA

3112 Windsor Road

Suite A356

White Paper CTWP009

1

The Secure Digital Card (SD Card, for short) was originally introduced to address the need for

reliable data storage in a small form factor for consumer hand-held and portable electronics, such

as cellphones, digital cameras, etc. Recently, there has been increasing interest to adopt the SD Card

for usage in industrial environments also.

Traditionally, the storage interface for industrial applications has been ATA, either in the form of

spec. is available only to SD Card Association members. However, the SD Card Association does make

available, for free, a simplied version of the physical layer spec., which is useful to help potential

end users to design in the SD Card in their systems. Anyone who is looking to use the SD Card in their

design should download this document, as it contains valuable information on the physical interface

and command protocols.

02.0

Just like the CF Card or PC Card, the SD Card contains an internal controller that handles all internal

ash memory operations. The data transfer between the host and the card is done in clock serial

mode, in 512 byte blocks. Currently, the dened le system is FAT12/16 for cards that are 2GByte or

Note the particularity with pad 9 placement and dierent width

for pad 8. This is due to legacy compatibility requirements with

MMC Cards.

03.1

2

Standard SD Cards operate at power supply range of 2.7 -3.3V. Special low voltage version SD Cards

can operate at a power supply level as low as 1.6V. Cactus Technologies SD Cards operate at the

standard voltage range.

can be congured to use a slower SPI mode. Protocol selection is done during the rst reset command

after power up. The SD Card powers up in SD mode. To switch the card to SPI mode, the CS signal

must be asserted while the host issues a reset command to the card. Once a particular protocol is

congured, it cannot be changed while power is applied. The only way to switch between protocol

modes is to do a power cycle.

Information in the remaining sections are for normal SD mode operation. Dierences between SD

mode and SPI mode are summarized in Section 5.0.

03.3

SD Cards operates in clock serial mode with bit widths of 1-4 bits. In SPI mode, the card operates in

03.5

All SD Cards contain a set of information registers which describe and control the various features

that the cards support. These are similar to the Card Conguration Registers and CIS Structure for

PC and CF Cards (or the Identify Drive structure for IDE drives). The following table is a list of the card

information registers and their descriptions:

03.6

3

Card Identication Number

on the CMD pin while data transfer is done on the DAT pins.

04.0

The format of a command token is as follows:

4

Association website.

06.0

There are two types of data packet format. One for normal byte wide data and the other for wide

width data which uses a 512 bit data block. Both types of data packets are protected with CRC16.

For normal 512 byte data transfers, the data is transferred least signicant byte rst but in the

individual byte, the data is transmitted MSB rst.

Data transfer can be done in 1-bit mode (using DAT0 only) or 4 -bit mode (if enabled, using DAT0 3).

When using 4 -bit mode, the byte data is formatted such that bit[7:4] are sent on DAT[3:0] followed by

bit[3:0] on DAT[3:0]. There are detailed diagrams of the formatting in the simplied SD Spec. from the

05.0

5

6

7

8

08.0