RM0090: Reference manual - STMicroelectronics

RM0090 Secure digital input/output interface (SDIO)
Data path
The data path subunit transfers data to and from cards. Figure 318 shows a block diagram
of the data path.
Figure 318. Data path
To control unit
Data FIFO
Transmit
Receive
Data path
Status
flag
Control
logic
Shift
register
Data
timer
ai14808
The card databus width can be programmed using the clock control register. If the 4-bit wide
bus mode is enabled, data is transferred at four bits per clock cycle over all four data signals
(SDIO_D[3:0]). If the 8-bit wide bus mode is enabled, data is transferred at eight bits per
clock cycle over all eight data signals (SDIO_D[7:0]). If the wide bus mode is not enabled,
only one bit per clock cycle is transferred over SDIO_D0.
Depending on the transfer direction (send or receive), the data path state machine (DPSM)
moves to the Wait_S or Wait_R state when it is enabled:
● Send: the DPSM moves to the Wait_S state. If there is data in the transmit FIFO, the
DPSM moves to the Send state, and the data path subunit starts sending data to a
card.
● Receive: the DPSM moves to the Wait_R state and waits for a start bit. When it
receives a start bit, the DPSM moves to the Receive state, and the data path subunit
starts receiving data from a card.
Data path state machine (DPSM)
The DPSM operates at SDIO_CK frequency. Data on the card bus signals is synchronous to
the rising edge of SDIO_CK. The DPSM has six states, as shown in Figure 319: Data path
state machine (DPSM).
CRC
SDIO_Din[7:0]
SDIO_Dout[7:0]
Doc ID 018909 Rev 3 852/1416