Memory Card Specification Sheet

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SDIO Simplified Specification Version 2.00

5. New I/O Read/Write Commands

Two additional data transfer instructions have been added to support I/O. IO_RW_DIRECT, a direct I/O

command similar to the MMC 'Fast I/O' command, and IO_RW_EXTENDED, which allows fast access with byte

or block addresses. Both commands are in class 9 (I/O Commands).

5.1 IO_RW_DIRECT Command (CMD52)

The IO_RW_DIRECT is the simplest means to access a single register within the total 128K of register space in

any I/O function, including the common I/O area (CIA). This command reads or writes 1 byte using only 1

command/response pair. A common use is to initialize registers or monitor status values for I/O functions. This

command is the fastest means to read or write single I/O registers, as it requires only a single

command/response pair.

S D Command

Index

110100b

R/W

flag

Function

Number

RAW

flag

Stuff Register Address Stuff Write Data

or Stuff Bits

CRC7 E

1 1 6 1 3 1 1 17 1 8 7 1

Figure 5-1 IO_RW_DIRECT Command

The IO_RW_DIRECT Command contains the following fields:

S(tart bit): Start bit. Always 0

D(irection): Direction. Always1 indicates transfer host to card.

Command Index: Identifies the “IO_RW_DIRECT” command with a value of 110100b

R/W Flag: This bit determines the direction of the I/O operation. If this bit is 0, this command

shall read data from the SDIO card at the address specified by the Function Number

and the Register Address to the host. The data byte is returned in the response, R5.

If this bit is set to 1, the command shall write the bytes in the Write Data field to the

I/O location addressed by the Function Number and the Register Address. If the

RAW flag is 0, then the data in the register that was written shall be read and that

value returned in the response.

RAW Flag: The Read after Write flag. If this bit is set to 1 and the R/W flag is set to 1, then the

command shall read the value of the register after the write. This is useful to allow

writing to a control register and reading the status at the same address. If this bit is

cleared, the value returned in the R5 response shall be the same as the write data in

the command. If this bit is set, the data field of the R5 response shall contain the

value read from the addressed register after the write operation.

Function Number: The number of the function within the I/O card you wish to read or write. Note that

function 0 selects the common I/O area (CIA).

There are 17 bits of address available so the register is located within the first 128K

(131,072) addresses of that function.

Write Data/Stuff Bits: For a direct write command (R/W=1), this is the byte that is written to the selected

address. For a direct read (R/W=0), this field is not used and shall be set to 0.

CRC7: 7 bits of CRC data

E(nd bit): End bit, always 1