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AT32F435/437
Series Reference Manual
2022.11.11
Page 568
Rev 2.03
25.4.2 SDIO clock control register (SDIO_ CLKCTRL)
The SDIO_CLKCTRL register controls the SDIO_CK output clock.
Bit
Register
Reset value
Type
Description
Bit 31: 17 Reserved
0x0000
resd
Kept at its default value.
Bit 16: 15 CLKDIV
0x0
rw
Clock division
This field is set or cleared by software. It defines the clock
division relations between the SDIOCLK and the
SDIO_CK: SDIO_CK frequency=SDIOCLK / [CLKDIV[9:
0] + 2].
Bit 14
HFCEN
0x0
rw
Hardware flow control enable
This bit is set or cleared by software.
0: Hardware flow control disabled
1: Hardware flow control enabled
Note: When hardware flow control is enabled, refer to the
SDIO_STS register for the meaning of the TXBUF_E and
RXBUF_F interrupt signals.
Bit 13
CLKEGS
0x0
rw
SDIO_CK edge selection
This bit is set or cleared by software.
0: SDIO_CK generated on the rising edge of the master
clock SDIOCLK
1: SDIO_CK generated on the falling edge of the master
clock SDIOCLK
Bit 12: 11 BUSWS
0x0
rw
Bus width selection
This bit is set or cleared by software.
00: Default bus mode, SDIO_D0 used
01: 4-bit bus mode,SDIO_D[3: 0] used
10: 8-bit bus mode, SDIO_D[7: 0] used
Bit 10
BYPSEN
0x0
rw
Clock divider bypass enable bit
This bit is set or cleared by software. When disabled, the
SDIO_CK output signal is driven by the SDIOCLK that is
divided according to the CLKDIV value. When enabled,
the SDIO_CK output signal is directly driven by the
SDIOCLK.
0: Clock divider bypass disabled
1: Clock divider bypass enabled
Bit 9
PWRSVEN
0x0
rw
Power saving mode enable
This bit is set or cleared by software. When disabled, the
SDIO_CK is always output; when enabled, the SDIO_CK
is only output when the bus is active.
0: Power saving mode disabled
1: Power saving mode enabled
Bit 8
CLKOEN
0x0
rw
Clock output enable
This bit is set or cleared by software.
0: Clock output disabled
1: Clock output enabled
Bit 7: 0
CLKDIV
0x00
rw
Clock division
This field is set or cleared by software. It defines the clock
division relations between the SDIOCLK and the
SDIO_CK: SDIO_CK frequency=SDIOCLK / [CLKDIV[9:
0] + 2].
Note: 1. While the SD/SDIO card or MultiMedia car is in identification mode, the SDIO_CK frequency
must be less than 400kHz.
2. When all card are assigned with relative card addresses, the clock frequency can be changed
to the maximum card frequency.
3. This register cannot be written within seven HCLK clock periods after data is written. The
SDIO_CK can be stopped during the read wait period for SD I/O cards. In this case, the SDIO_
CLKCTRL register does not control the SDIO_CK.