Initialization Role of CKE

During power-up, CKE is the only input to the SDRAM that has its level recognized (other than the reset pin) once power is applied. It should be driven LOW by the DDR controller to make sure the SDRAM components float DQ and DQS during power-up. CKE signals remain LOW (while any reset is active) until the BIOS writes to a configuration register. Using this method, CKE is ensured to remain inactive for much longer than the specified 200 micro-seconds after power and clocks to SDRAM devices are stable. In LPDDR5/DDR5, there is no CKE pin and the power management roll is assumed by the CS signals.