STM8S datasheet(274/467 Pages) STMICROELECTRONICS

274 / 467 page

Serial peripheral interface (SPI)

RM0016

274/467

DocID14587 Rev 14

Figure 98. RXNE behavior in receive-only mode (BDM = 0 and RXONLY = 1).

Case of continuous transfers

Bidirectional receive procedure (BDM = 1 and BDOE = 0)

In this mode, the procedure is similar to the Receive-only procedure except that the BDM bit

must be set and the BDOE bit must be reset in the SPI_CR2 register before enabling the

SPI.

Continuous and discontinuous transfers

When transmitting data in master mode, if the software is fast enough to detect each TXE

rising edge (or TXE interrupt) and to immediately write the SPI_DR register before the

ongoing data transfer is complete, the communication is said to be continuous. In this case,

there is no discontinuity in the generation of the SPI clock between each data and the BSY

bit will never be reset between each data transfer.

On the contrary, if the software is not fast enough, this can lead to some discontinuities in

the communication. In this case, the BSY bit is reset between each data transmission (see

Figure 99).

In master receive-only mode (BDM = 0 and RXONLY = 1) or in bidirectional receive mode

(BDM = 1 and BDOE = 0), the communication is always continuous and the BSY flag is

always read at 1.

In slave mode, the continuity of the communication is decided by the SPI master device. But

even if the communication is continuous, the BSY flag goes low between each transfer for a

minimum duration of one SPI clock cycle (see Figure 95).

STM8S Datasheet(PDF) 274 Page - STMicroelectronics