SWCU194 March 2023 CC1314R10 , CC1354P10 , CC1354R10 , CC2674P10 , CC2674R10
Figure 23-2 shows the TI synchronous serial frame format for a single transmitted frame.
SPIn_CLK and SPIn_CS are forced low and the transmit data line SPIn_MOSI is put in tristate whenever the SPI is idle. When the bottom entry of the TX FIFO contains data, SPIn_CS is pulsed high for one SPIn_CLK period.
The transmitted value is also transferred from the TX FIFO to the serial shift register of the transmit logic. On the next rising edge of SPIn_CLK, the MSB of the 4-bit to 32-bit data frame is shifted out on the SPIn_MOSI pin. Likewise, the MSB of the received data is shifted onto the SPIn_MISO pin by the off-chip serial slave device.
Both the SPI and the off-chip serial slave device then clock each data bit into their serial shifter on each falling edge of SPIn_CLK. The received data is transferred from the serial shifter to the RX FIFO on the first rising edge of SPIn_CLK after the least significant bit (LSB) is latched.
Figure 23-3 shows the TI synchronous serial frame format when back-to-back frames are transmitted.