SWCU194 March 2023 CC1314R10 , CC1354P10 , CC1354R10 , CC2674P10 , CC2674R10
The common TX FIFO is a 32 bit wide, 8 location deep, first-in first-out memory buffer. The CPU writes data to the FIFO by writing the SPI TX Data register, SPI:TXDATA, and data is stored in the FIFO until it is read out by the transmission logic.
When configured as a master (or a slave), parallel data is written into the TX FIFO before serial conversion and transmission to the attached slave or master, respectively, through the SPIn_MOSI (or SPIn_MISO) pin via SPIn_TX output.
In slave mode, the SPI transmits data each time the master initiates a transaction. If the TX FIFO is empty and the master initiates a transaction, the slave transmits garbage data. User or software is responsible to ensure valid data is available in the FIFO as needed. The SPI can be configured to generate an interrupt when a configurable level within the FIFO is selected via SPI:IFLS, or a µDMA single request when the FIFO is not FULL.