481
/
838
Nations Technologies Inc.
Tel
:
+86-755-86309900
:
Address: Nations Tower, #109 Baoshen Road, Hi-tech Park North.
Nanshan District, Shenzhen, 518057, P.R.China
Bit
Width
Value
Description
[45:40]
6
‘101000’
CMD40
[39:8]Argument
field
[31:16]
16
x
RCA[31:16] of a successful card or host
[15:0]
16
x
Undefined. Can be used as interrupt data.
[7:1]
7
x
CRC7
0
1
1
End bit
When sending a CMD3 command to an I/O-only card, the card's status bits[23:8] will change, and bit 16 in the
response is the value in the I/O-only SD card, bit 15 is COM_CRC_ERROR, Bit 14 is ILLEGAL_COMMAND, Bit
13 is ERROR, Bits[12:0] are reserved.
Hardware flow control
Using the hardware flow control function can avoid FIFO underflow (transmit mode) and overflow (receive mode)
errors.
The operation process of hardware flow control is to stop SDIO_CLK and freeze the SDIO state machine. When the
FIFO cannot send and receive data, the data transmission is suspended. It should be noted that only the state machine
driven by SDIO_CLK is frozen, the AHB interface is still working. Even when flow control is in effect, the FIFO
can still be read from or written to.
The SDIO_CLKCTRL.HWCLKEN bit must be set to '1' to enable hardware flow control. After reset, the hardware
flow control function is automatically turned off.
SDIO register
Devices communicate with the system through control registers. The width of the control registers is 32 bits wide,
and these registers can be manipulated on the AHB bus. Note that these peripheral registers must be manipulated in
word (32 bits).