SPRUIE9D May 2017 – May 2024 DRA74P , DRA75P , DRA76P , DRA77P
The slave receive mode is programmable (set the MCSPI_CHxCONF[13:12] TRM bit field [where x = 0] to 0x1).
In receive-only mode, the MCSPI_TXx register must be loaded before the McSPI is selected by an external SPI master device. The MCSPI_TXx register content is always loaded into the shift register whether it is updated or not. The TXx_UNDERFLOW event is activated accordingly and does not prevent transmission.
When the SPI word transfer completes (the MCSPI_CHxSTAT0[2] EOT bit [where x = 0] is set to 1), the received data is transferred to the channel receive register.
To use the McSPI as a slave receive-only device, the TXx_EMPTY and TXx_UNDERFLOW interrupts and the DMA write requests must be disabled due to the state of the MCSPI_TXx register.
For a full-duplex transmission, the serial clock (SPICLK) synchronizes shifting and sampling of the information on the single serial data line. For full duplex, two data lines are required. If SPICLK synchronizes on a single serial data line, the data line should be half-duplex.
Figure 26-90 shows a half-duplex system with a master device on the left and a receive-only slave device on the right. Each time a bit transfers out from the master, 1 bit transfers in from the slave. After eight cycles of the serial clock SPICLK, WordA transfers from the master to the slave.