17.5.9.1 DDR3 Devices

ZQCL (ZQ Calibration Long) command is used as follows:

To perform the initial calibration during the power-up initialization sequence. This command is allowed a timing period of tZQinit determined by INIT5. dev_zqinit_x32 (see Register Descriptions) to perform full calibration and the transfer of values.
To perform long ZQ Calibration after exiting from Self-refresh mode. This command is allowed a timing period of tZQOPER, determined by ZQCTL0._t_zq_long_nop. This command is automatically issued when ZQCTL0.dis_srx_zqcl (ZQCTL0.dis_mpsmx_zqcl) is set to 0. To disable issuing ZQCL after self-refresh exit, set ZQCTL0.dis_srx_zqcl (ZQCTL0.dis_mpsmx_zqcl) to 1.

ZQCS (ZQ Calibration Short) command is used to perform periodic calibration to account for VT (Voltage/Temperature) variations. A shorter timing window is provided to perform calibration and transfer of values as defined by the timing parameter tZQCS (determined by ZQCTL0._t_zq_short_nop). ZQCS can be performed automatically on a regular interval or through direct software request. For more information, see Automatic and Software Initiated ZQCS.

In DDR3 mode, the ZQ Calibration commands are sent out encoded on the DFI command bus as mentioned in the JEDEC Specification. The UDDRC performs no other activities for the duration of tZQinit, tZQOPER and tZQCS. The quiet time on the SDRAM channel helps in accurate calibration of SDRAM RON and ODT. All banks are precharged and t_RP met before the UDDRC issues the ZQ Calibration commands.