57.13.1.5.1.2 Host Read Mode

${\mathit{\text{f}}}_{\mathrm{QSCK}}\text{max}=\frac{1}{\mathit{\text{Q}}\mathit{\text{S}}\mathit{\text{P}}{\mathit{\text{I}}}_0\left({\text{or}\mathit{\text{Q}}\mathit{\text{S}}\mathit{\text{P}}\mathit{\text{I}}}_3\right)+{\mathit{\text{t}}}_{\mathrm{VALID}}}$

Where,

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

For a QSPI Client device with t_VALID (or t_V) = 12 ns, f_QSCK max = 66 MHz at VDDIO = 3.3V.

For a QSPI Flash memory device with t_VALID (or t_V) = 6 ns, the formula returns a value of 112 MHz. In worst case conditions, this exceeds 66 MHz, which is the maximum allowed frequency of the QSPI Host. In this case, the limitation is due to the controller and not the Client.