ST STM32F405 User Manual

Serial peripheral interface (SPI) RM0090
884/1749 RM0090 Rev 18
Figure 252. TI mode - master mode, continuous transfer
28.3.4 Configuring the SPI for half-duplex communication
The SPI is capable of operating in half-duplex mode in 2 configurations.
• 1 clock and 1 bidirectional data wire
• 1 clock and 1 data wire (receive-only or transmit-only)
1 clock and 1 bidirectional data wire (BIDIMODE = 1)
This mode is enabled by setting the BIDIMODE bit in the SPI_CR1 register. In this mode
SCK is used for the clock and MOSI in master or MISO in slave mode is used for data
communication. The transfer direction (Input/Output) is selected by the BIDIOE bit in the
SPI_CR1 register. When this bit is 1, the data line is output otherwise it is input.
1 clock and 1 unidirectional data wire (BIDIMODE = 0)
In this mode, the application can use the SPI either in transmit-only mode or in receive-only
mode.
• Transmit-only mode is similar to full-duplex mode (BIDIMODE=0, RXONLY=0): the
data are transmitted on the transmit pin (MOSI in master mode or MISO in slave mode)
and the receive pin (MISO in master mode or MOSI in slave mode) can be used as a
general-purpose IO. In this case, the application just needs to ignore the Rx buffer (if
the data register is read, it does not contain the received value).
• In receive-only mode, the application can disable the SPI output function by setting the
RXONLY bit in the SPI_CR1 register. In this case, it frees the transmit IO pin (MOSI in
master mode or MISO in slave mode), so it can be used for other purposes.
To start the communication in receive-only mode, configure and enable the SPI:
• In master mode, the communication starts immediately and stops when the SPE bit is
cleared and the current reception stops. There is no need to read the BSY flag in this
mode. It is always set when an SPI communication is ongoing.
• In slave mode, the SPI continues to receive as long as the NSS is pulled down (or the
SSI bit is cleared in NSS software mode) and the SCK is running.
ai18437
MSBOUT
MOSI
output
NSS
output
SCK
output
trigger sampling trigger sampling trigger sampling
DONTCARE LSBOUT
DONTCARE
MISO
intput
1 or 0 MSBIN
LSBIN
MSBOUT LSBOUT
MSBIN LSBIN
FRAME 1 FRAME 2

ST STM32F405 Specifications

General

Brand	ST
Model	STM32F405
Category	Computer Hardware
Language	English