Receive Only Mode

When RXR is set and TXR is clear, the SPI host is in Receive Only mode. In this mode, data transfers when the receive FIFO is not full and the transfer counter is nonzero. In this mode, writing a value to SPIxTCNTL will start the clocks for transfer. The clocks will suspend while the receive FIFO is full and cease when the SPIxTCNT reaches zero (see the Transfer Counter section). If there is any data in the transmit FIFO, the first data written to SPIxTXB will be transmitted on each data exchange, although the transmit FIFO occupancy will not change, meaning that the same message will be sent on each transmission. If there is no data in the transmit FIFO, the most recently received data will be transmitted. The following figure shows an example of sending a command using the Transmit Only mode and then receiving a byte of data using the Receive Only mode.

Important: When operating in Receive Only mode and the size of every SPI transaction is less than 8 bits, it is recommended to operate in BMODE = 1 mode. The size of the packet can be configured using the SPIxTWIDTH register.
Figure 1. SPI Host Operation - Command+Read Data, TXR = 0, RXR = 1