19.4.1.3.1 Standard Buffer Mode

The SPIx Data Receive/Transmit Buffer (SPIxBUF) register is actually two separate internal registers: the Transmit Buffer (SPIxTXB) and the Receive Buffer (SPIxRXB). These two unidirectional registers share the SFR address of SPIxBUF.

When a complete byte/word is received, it is transferred from SPIxRXSR to SPIxRXB and the SPIRBF bit is set. If the software reads the SPIxBUF buffer, the SPIRBF bit is cleared.

As the software writes to SPIxBUF, the data is loaded into the SPIxTXB and the SPITBF bit is set by hardware. As the data is transmitted out of SPIxTXSR, the SPITBF bit is cleared.

The SPI module double-buffers transmit/receive operations and allows continuous data transfers in the background. Transmission and reception occur simultaneously in SPIxTXSR and SPIxRXSR, respectively.