GD32W51x User Manual
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open-drain for initialization (only for MMC3.31 or previous), and push-pull for command
transfer (SD/SD I/O card MMC4.2 use push-pull drivers also for initialization).
SDIO_D[7:0]
: These are bidirectional data channels. The D signals operate in push-pull mode.
Only the card or the host is driving these signals at a time. By default, after power up or reset,
only D0 is used for data transfer. A wider data bus can be configured for data transfer, using
either D0-D3 or D0-D7 (just for MMC4.2), by the SDIO controller. The SDIO includes internal
pull-ups for data lines D1-D7. Right after entering to the 4-bit mode the card disconnects the
internal pull-ups of lines D1 and D2 (D3 internal pull-up is left connected due to the SPI mode
CS usage). Correspondingly right after entering to the 8-bit mode the card disconnects the
internal pull-ups of lines D1, D2 and D4-D7.
Table 23-1. SDIO I/O definitions
Pin function
Direction
Description
SDIO_CK
O
SD/SD I/O /MMC clock
SDIO_CMD
I/O
Command input/output
SDIO_D[7:0]
I/O
Data input/output for data lines D[7:0]
The SDIO adapter is an interface to SD/SD I/O /MMC/CE-ATA. It consists of three subunits:
Control unit
The control unit contains the power management functions and the clock management
functions for the memory card clock. The power management is controlled by SDIO_PWRCTL
register which implements power off or power on. The power saving mode configured by
setting CLKPWRSAV bit in SDIO_CLKCTL register, which implements close the SDIO_CK
when the bus is idle. The clock management generates SDIO_CK to card. The SDIO_CK is
generated by a divider of SDIOCLK when CLKBYP bit in SDIO_CLKCTL register is 0, or
directly SDIOCLK when CLKBYP bit in SDIO_CLKCTL register is 1.
The Hardware clock control is enabled by setting HWCLKEN in SDIO_CLKCTL register. This
functionality is used to avoid FIFO underrun and overrun errors by hardware control the
SDIO_CK on/off depending on the system bus is very busy or not. When the FIFO cannot
receive or transmit data, the host will stop the SDIO_CK and freeze SDIO state machines to
avoid the corresponded error. Only state machines are frozen, the APB2 interface is still alive.
So, the FIFO can access by APB2 bus.
Command unit
The command unit implements command transfer to the card. The data transfer flow is
controlled by Command State Machine (CSM). After a write operation to SDIO_CMDCTL
register and CSMEN in SDIO_CMDCTL register is 1, the command transfer starts. It firstly
sends a command to the card. The command contains 48 bits send by SDIO_CMD signal
which sends 1 bits to card at one SDIO_CK. The 48 bits command contains 1 bit Start bit, 1
bit Transmission bit, 6 bits command index defined by CMDIDX bits in SDIO_CMDCTL
register, 32 bits argument defined in SDIO_CMDAGMT register, 7 bits CRC, and 1 bit end bit.
Содержание GD32W515 Series
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