New I/O Read/Write Commands; Io_Rw_Direct Command (Cmd52); Io_Rw_Extended Command (Cmd53); Cmd53 Data Transfer Format - SD Association SD-501 Specifications

SDIO Simple Specification Version 1.0
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.
The SDIO card's response to CMD52 will be in one of two formats. If the communication between the card and
host is in the 1-bit or 4-bit SD mode, the response will be in a 48-bit response (R5). If the communication is
using the SPI mode, the response will be a 16-bit R5 response.
5.2

IO_RW_EXTENDED command (CMD53)

In order to read and write multiple I/O registers with a single command, a new command, IO_RW_EXTENDED
is defined. This command is included in command class 9 (I/O Commands). This command allows the reading
or writing of a large number of I/O registers with a single command. Since this is a data transfer command, it
provides the highest possible transfer rate.
The response from the SDIO card to CMD53 will be R5 (the same as CMD52). For CMD53, the 8-bit data field
will be stuff bits and shall be read as 0x00.
5.2.1

CMD53 Data Transfer Format

When executing the IO_RW_EXTENDED (CMD53), the multi-byte or multi-block data transfer is similar to the
data transfer for memory. For the multi-byte transfer modes (block mode=0) the following applies:
IO_RW_EXTENDED byte read is similar to CMD17 (READ_SINGLE_BLOCK)
IO_RW_EXTENDED byte write is similar to CMD24 (WRITE_BLOCK)
Note that the byte count for this transfer is set in the command, rather than the fixed block size. Thus, the size
of the data payload will be in the range of 1-512 bytes. The block mode is similar to the following memory
commands:
IO_RW_EXTENDED block read is similar to CMD18 (READ_MULTIPLE_BLOCK)
IO_RW_EXTENDED block write is similar to CMD25 (WRITE_MULTIPLE_BLOCK)
For the block mode the only difference is that for a fixed block count, the host does not need to stop the
transfer, as it will continue until the block count is satisfied. If the block count is set to zero, the operation is
identical to the memory mode in that the host must stop the transfer.
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