50.6.1.1.2 Host Read in Single Data Rate Mode

${\mathit{\text{f}}}_{\mathrm{QSCK}}\text{max}=\frac{1}{\mathit{\text{Q}}\mathit{\text{S}}\mathit{\text{P}}{\mathit{\text{I}}}_0+{\mathit{\text{t}}}_{\mathrm{VALID}}}$

t_VALID is the client time response to output data after detecting a QSCK edge.

For a QSPI SPI Mode client device with t_VALID (or t_V) = 12 ns, with QSPI₀ = 1.8ns, f_QSCKmax = 72.4 MHz.

For a QSPI Flash memory device with t_VALID (or t_V) = 6 ns, and QSPI₀ = 1.0ns, the formula returns a value of 128 MHz. In worst case conditions, this exceeds the maximum allowed frequency of the QSPI. In this case, the limitation is due to the controller and not to the client.