GD32F10x User Manual
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a one bit transfer on the command line (SDIO_CMD) and on all the data lines (SDIO_DAT).
The SDIO_CLK frequency can vary between 0 MHz and 20 MHz for a Multimedia Card V3.31,
between 0 and 48 MHz for a Multimedia Card V4.2, or between 0 and 25 MHz for an SD/SD
I/O card.
The SDIO uses two clock signals: SDIO adapter clock (SDIOCLK = HCLK) and AHB bus
clock (HCLK/2)
SDIO_CMD
: This signal is a bidirectional command channel used for card initialization and
transfer of commands. Commands are sent from the SDIO controller to the card and
responses are sent from the card to the host. The CMD signal has two operation modes:
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_DAT[7:0]
: These are bidirectional data channels. The DAT 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 DAT0 is used for data transfer. A wider data bus can be configured for data
transfer, using either DAT0-DAT3 or DAT0-DAT7 (just for MMC4.2), by the SDIO controller.
The SDIO includes internal pull-ups for data lines DAT1-DAT7. Right after entering to the 4-
bit mode the card disconnects the internal pull-ups of lines DAT1 and DAT2 (DAT3 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 DAT1, DAT2 and DAT4-
DAT7.
Table 19-1. SDIO I/O definitions
Pin function
Direction
Description
SDIO_CLK
O
SD/SD I/O /MMC clock
SDIO_CMD
I/O
Command input/output
SDIO_DAT[7:0]
I/O
Data input/output for data lines DAT[7:0]
The SDIO adapter is an interface to SD, SD I/O, MMC and 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_CLK
when the bus is idle. The clock management generates SDIO_CLK to card. The SDIO_CLK
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_CLK on/off depending on the system bus is very busy or not. When the FIFO cannot
Summary of Contents for GD32F10 Series
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Page 416: ...GD32F10x User Manual 416 shadow register updates every update event ...
Page 427: ...GD32F10x User Manual 427 value ...
Page 518: ...GD32F10x User Manual 518 These bits are not used in SPI mode ...