Table 155. Transmit Fifo Status Flags - STMicroelectronics STM32F405 Reference Manual

Advanced arm-based 32-bit mcus
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Secure digital input/output interface (SDIO)
Data FIFO
The data FIFO (first-in-first-out) subunit is a data buffer with a transmit and receive unit.
The FIFO contains a 32-bit wide, 32-word deep data buffer, and transmit and receive logic.
Because the data FIFO operates in the APB2 clock domain (PCLK2), all signals from the
subunits in the SDIO clock domain (SDIOCLK) are resynchronized.
Depending on the TXACT and RXACT flags, the FIFO can be disabled, transmit enabled, or
receive enabled. TXACT and RXACT are driven by the data path subunit and are mutually
exclusive:
Transmit FIFO:
Data can be written to the transmit FIFO through the APB2 interface when the SDIO is
enabled for transmission.
The transmit FIFO is accessible via 32 sequential addresses. The transmit FIFO
contains a data output register that holds the data word pointed to by the read pointer.
When the data path subunit has loaded its shift register, it increments the read pointer
and drives new data out.
If the transmit FIFO is disabled, all status flags are deasserted. The data path subunit
asserts TXACT when it transmits data.
Flag
TXFIFOF
TXFIFOE
TXFIFOHE
TXDAVL
TXUNDERR
Receive FIFO
When the data path subunit receives a word of data, it drives the data on the write
databus. The write pointer is incremented after the write operation completes. On the
read side, the contents of the FIFO word pointed to by the current value of the read
pointer is driven onto the read databus. If the receive FIFO is disabled, all status flags
are deasserted, and the read and write pointers are reset. The data path subunit
asserts RXACT when it receives data.
The receive FIFO is accessible via 32 sequential addresses.
1024/1731
The transmit FIFO refers to the transmit logic and data buffer when TXACT is
asserted
The receive FIFO refers to the receive logic and data buffer when RXACT is
asserted

Table 155. Transmit FIFO status flags

Set to high when all 32 transmit FIFO words contain valid data.
Set to high when the transmit FIFO does not contain valid data.
Set to high when 8 or more transmit FIFO words are empty. This flag can be used
as a DMA request.
Set to high when the transmit FIFO contains valid data. This flag is the inverse of
the TXFIFOE flag.
Set to high when an underrun error occurs. This flag is cleared by writing to the
SDIO Clear register.
DocID018909 Rev 11
Description
Table 156
lists the receive FIFO status flags.
RM0090

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