Serial peripheral interface/ inter-IC sound (SPI/I2S) RM0367
884/1043 RM0367 Rev 7
31.3.7 SPI configuration
The configuration procedure is almost the same for master and slave. For specific mode
setups, follow the dedicated chapters. When a standard communication is to be initialized,
perform these steps:
1. Write proper GPIO registers: Configure GPIO for MOSI, MISO and SCK pins.
2. Write to the SPI_CR1 register:
a) Configure the serial clock baud rate using the BR[2:0] bits (Note: 3).
b) Configure the CPOL and CPHA bits combination to define one of the four
relationships between the data transfer and the serial clock. (Note: 2 - except the
case when CRC is enabled at TI mode).
c) Select simplex or half-duplex mode by configuring RXONLY or BIDIMODE and
BIDIOE (RXONLY and BIDIMODE can't be set at the same time).
d) Configure the LSBFIRST bit to define the frame format (Note: 2).
e) Configure the CRCEN and CRCEN bits if CRC is needed (while SCK clock signal
is at idle state).
f) Configure SSM and SSI (Note: 2).
g) Configure the MSTR bit (in multimaster NSS configuration, avoid conflict state on
NSS if master is configured to prevent MODF error).
h) Set the DFF bit to configure the data frame format (8 or 16 bits).
3. Write to SPI_CR2 register:
a) Configure SSOE (Note: 1 & 2).
b) Set the FRF bit if the TI protocol is required.
4. Write to SPI_CRCPR register: Configure the CRC polynomial if needed.
5. Write proper DMA registers: Configure DMA streams dedicated for SPI Tx and Rx in
DMA registers if the DMA streams are used.
Note: (1) Step is not required in slave mode.
(2) Step is not required in TI mode.
(3) The step is not required in slave mode except slave working at TI mode.
For code example, refer to A.19.1: SPI master configuration code example and A.19.2: SPI
slave configuration code example.
31.3.8 Procedure for enabling SPI
It is recommended to enable the SPI slave before the master sends the clock. Otherwise,
undesired data transmission might occur. The slave data register must already contain data
to be sent before starting communication with the master (either on the first edge of the
communication clock, or before the end of the ongoing communication if the clock signal is
continuous). The SCK signal must be settled at an idle state level corresponding to the
selected polarity before the SPI slave is enabled.
At full-duplex (or in any transmit-only mode), the master starts communicating when the SPI
is enabled and data to be sent is written in the Tx Buffer.
In any master receive-only mode (RXONLY=1 or BIDIMODE=1 & BIDIOE=0), the master
starts communicating and the clock starts running immediately after the SPI is enabled.
The slave starts communicating when it receives a correct clock signal from the master. The
slave software must write the data to be sent before the SPI master initiates the transfer.
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