49.6.2 Serial Clock Phase and Polarity

All combinations of polarity and phase are available when QSPI operates in SPI mode (QSPI_MR.SMM=0).

In QSPI Serial Memory mode (QSPI_MR.SMM=1), only Mode 0 is supported.

The clock polarity is programmed with the CPOL bit in the QSPI Serial Clock register (QSPI_SCR). QSPI_SCR.CPHA programs the clock phase. These two parameters determine the edges of the clock signal on which data is driven and sampled. Each of the two parameters has two possible states, resulting in four possible combinations that are incompatible with one another. Thus, the interfaced client must use the same parameter values to communicate.

The table below shows the four modes and corresponding parameter settings.

Table 49-2. QSPI Bus Clock Modes
QSPI Clock Mode QSPI_SCR.CPOL QSPI_SCR.CPHA Host Shift QSCK
 Edge Client Capture QSCK Edge QSCK Inactive Level
0 (QSPI, SPI) 0 0 Falling Falling Low
1 (SPI) 0 1 Rising Rising Low
2 (SPI) 1 0 Rising Rising High
3 (SPI) 1 1 Falling Falling High

The following figures show examples of data transfers.

Figure 49-2. QSPI Transfer Format (QSPI_SCR.CPHA = 0, 8 bits per transfer), Mode 0 and 2
Figure 49-3. QSPI Transfer Format (QSPI_SCR.CPHA = 1, 8 bits per transfer), Mode 1 and 3