SDIO PHYSICAL LAYER

4.7 Commands
4.7.1 Command Types
There are four kinds of commands defined to control the SD Memory Card:
• broadcast commands (bc), no response - The broadcast feature is only if all the CMD lines are
connected together in the host. If they are separated then each card will accept it separately on
his turn.
• broadcast commands with response (bcr)
response from all cards simultaneously - Since there is no Open Drain mode in SD Memory
Card this type of commands shall be used only if all the CMD lines are separated - the command

will be accepted and responded by every card separately.

• addressed (point-to-point) commands (ac)
no data transfer on DAT
• addressed (point-to-point) data transfer commands (adtc)
data transfer on DAT
All commands and responses are sent over the CMD line of the SD Memory Card. The command
transmission always starts with the left bit of the bitstring corresponding to the command codeword.

4.7.2 Command Format
All commands have a fixed code length of 48 bits, needing a transmission time of 2.4 μs @ 20 MHz

A command always starts with a start bit (always ‘0’), followed by the bit indicating the direction of
transmission (host = ‘1’). The next 6 bits indicate the index of the command, this value being interpreted
as a binary coded number (between 0 and 63). Some commands need an argument (e.g. an
address), which is coded by 32 bits. A value denoted by ‘x’ in the table above indicates this variable
is dependent on the command. All commands are protected by a CRC (see Chapter 4.5 for the definition
of CRC7). Every command codeword is terminated by the end bit (always ‘1’). All commands
and their arguments are listed in Table 14-Table 22.

In sd_part1_v1.10_2005.pdf P61