25.2.1 Block Diagram

The SPI is built around an 8-bit Shift register that will shift data out and in at the same time. The Transmit Data register and the Receive Data register are not physical registers but are mapped to other registers when written or read: Writing the Transmit Data register (SPIn.DATA) will write the Shift register in Normal mode and the Transmit Buffer register in Buffer mode. Reading the Receive Data register (SPIn.DATA) will read the First Receive Buffer register in normal mode and the Second Receive Data register in Buffer mode.

In Master mode, the SPI has a clock generator to generate the SCK clock. In Slave mode, the received SCK clock is synchronized and sampled to trigger the shifting of data in the Shift register.