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AT32F435/437
Series Reference Manual
2022.11.11
Page 562
Rev 2.03
register where the CLKDIV bit is used to define the divider factor between the SDIOCLK and the SDIO
output clock. If BYPSEN = 0, the SDIO_CK output signal is driven by the SDIOCLK divided according
to the CLKDIV bit; if BYPSEN = 1, the SDIO_CK output signal is directly driven by the SDIOCLK. The
HFCEN is set to enable hardware flow control feature in order to avoid the occurrence of an error at
transmission underflow or reception overflow. The PWRSVEN bit can be set by software to enable power
save mode, and the SDIO_CK can be output only when the bus is active.
Command path
The command path unit sends commands to and receives responses from the cards. When the
CCSMEN bit is set in the SDIO_CMDCTRL register, a command transfer starts. First sends a command
to a card by the SDIO_CMD, the command length is 48 bits. The data on the SDIO_CMD is synchronized
with the rising edge of the SDIO_CK. A block of data is transferred with each SDIO_CK, including start
bit, transfer bit, command index defined by the SDIO_CMDCTRL_CMDIDX bit, parameters defined by
the SDIO_ARG, 7-bit CRC and end bit. Then receives responses from the card. There are two response
types: 48-bit short response and 136-bit long response. Both use CRC error check. The received
responses are saved in the area from SDIO_RSP1 to SDIO_RSP4. The command path can generate
command flag, which can be defined by the SDIO_STS register.
Table 25-19
Command formats
Bit
47
46
[45: 40 ]
[ 39: 8 ]
[ 7: 1 ]
0
Width
1
1
6
32
7
1
Value
0
1
-
-
-
1
Description
Start bit
Tx bit
Command
index
Parameter
CRC7
End bit
─
Response: A response is sent from a specified card to the host (or synchronously from all cards for
MMCV3.31 or previous), as an answer to a previously received command. Responses are transferred
serially on the CMD line.
Table 25-20
Short response format
Bit
47
46
[45: 40 ]
[ 39: 8 ]
[ 7: 1 ]
0
Width
1
1
6
32
7
1
Value
0
0
-
-
-
1
Description
Start bit
Tx bit
Command
index
Parameter
CRC7
(or 1111111)
End bit
Table 25-21
Long response format
Bit
135
134
[133: 128]
[ 127: 1 ]
0
Width
1
1
6
127
1
Value
0
0
111111
-
1
Description
Start bit
Tx
Reserved
CID or CSD
(including
internal CRC7)
End bit