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SDIO_CLK: Clock provided by SDIO controller to the card. Each clock
cycle directly transmits 1-bit command or data on the command line
(SDIO_ CMD) and all data lines (SDIO)_ D). SDIO_ CLK frequency is
within 0-20MHz for MMC card V3.31, within 0-48MHz for MMC card
V4.2, and within 0-25MHz for SD or SD I/O card.
SDIO_CMD: The signal is a bidirectional command channel, which is
used for card initialization and command transmission. Command is
sent from SDIO controller to the card, and the response is sent from
the card to the master. There are two operation modes of CMD signal:
the open-drain mode of initialization (used for MMC card V3.31 and
previous versions) and the push-pull mode of command transmitting
(SD, SD I/O, and MMC card V4.2 initialization are also push-pull
mode).
SDIO_D[7:0]: The signal lines are bidirectional data channels and in
push-pull mode. By default, after power-on or reset, only D0 is used
for data transmission. SDIO adapter can be configured with wider
data bus for data transmission, using D0-D3 and D0-D7 (only on
MMC V4.2).
Control unit
The control unit includes power management and clock management functions.
Command unit
The command unit realizes transmitting commands to the card and receiving
commands from the card, and the data transmission is controlled by the
command state machine (CPSM).
Command state machine
CS_Idle gets ready to transmit the command after
reset
1. CPSM is enabled and WAITDEND is enabled CS_Pend
2. CPSM is enabled and WAITDEND is disabled CS_Send
3. CPSM is turned off
CS_Idle
Note: The idle state of command state machine is maintained for
at least 8 SDI0_CLK cycles, so as to meet the timing restriction
of N
CC
and N
R C
.
N
CC
: Minimum time interval between two host commands
N
RC
: Minimum time interval between host command and card response
CS_Pend waits for the end of data
transmission
1. Dat a transmissi on is com plet ed
CS_Send
2. CPSM i s turned off
CS_Idl e