Memory Card Specification Sheet

SDIO Simplified Specification Version 2.00

2. SDIO Signaling Definition

2.1 SDIO Card Types

This specification defines two types of SDIO cards. The Full-Speed card supports SPI, 1-bit SD and the 4-bit SD

transfer modes at the full clock range of 0-25MHz. The Full-Speed SDIO cards have a data transfer rate of over

100 Mb/second (10 MB/Sec). A second version of the SDIO card is the Low-Speed SDIO card. This card

requires only the SPI and 1-bit SD transfer modes. 4-bit support is optional. In addition, Low-Speed SDIO cards

shall support a full clock range of 0-400 KHz. The intended use of Low-Speed cards is to support low-speed I/O

capabilities with a minimum of hardware. The Low-Speed cards support such functions as modems, bar-code

scanners, GPS receivers etc. If a card is a ‘Combo card’ (memory plus SDIO) then Full-Speed and 4-bit

operation is mandatory for both the memory and SDIO portions of the card.

2.2 SDIO Card modes

There are 3 signaling modes defined for SD memory cards that also apply to SDIO Card:

2.2.1 SPI (Card mandatory support)

The SPI bus topology is defined in section 3.5.2 and the protocol is defined in sections 3.6.2 and 7 of the SD

Physical Specification Version 2.00. In this mode pin 8, which is undefined for memory, is used as the

interrupt pin. All other pins and signaling protocols are identical to the SD Physical Specification.

2.2.2 1-bit SD Data Transfer Mode (Card Mandatory Support)

This mode is identical to the 1 data bit (narrow) mode defined for SD Memory in section 3.6.1 of the SD

Physical Specification. In this mode, data is transferred on the DAT[0] pin only. In this mode pin 8, which is

undefined for memory, is used as the interrupt pin. All other pins and signaling protocols are identical to the

SD Memory specification.

2.2.3 4-bit SD Data Transfer Mode (Mandatory for High-Speed Cards, Optional for Low-Speed)

This mode is identical to the 4 data bit mode (wide) defined for SD Memory in section 3.6.1 of the SD

Physical Specification. In this mode, data is transferred on all 4 data pins (DAT[3:0]). In this mode the

interrupt pin is not available for exclusive use as it is utilized as a data transfer line. Thus, if the interrupt

function is required, a special timing is required to provide interrupts. See section 8.1.2 for details of this

operation. The 4-bit SD mode provides the highest data transfer possible, up to 100 Mb/sec.

2.3 SDIO Host Modes

If a SDIO aware host supports the SD transfer mode, it is recommended that both the 1-bit and 4-bit modes be

supported. While a SDIO host that supports only the 4-bit transfer mode is possible, its performance with a

Low-Speed SDIO card may be reduced. This is because the only means to transfer data to and from a

Low-Speed card would be the single byte per command transfer (using the IO_RW_DIRECT command

(CMD52) see 5.1).