SPRUI30H November 2015 – May 2024 DRA745 , DRA746 , DRA750 , DRA756
The EMIF controller supports automatic output impedance (ZQ) calibration for DDR3 memories. This feature is supported by DDR3 and not supported by DDR2 memories. The ZQ calibration can be enabled by setting to 0x1 the EMIF_SDRAM_OUTPUT_IMPEDANCE_CALIBRATION_CONFIG[30] ZQ_CS0EN bit. The EMIF supports three types of ZQ calibration commands:
The EMIF automatically issues ZQINIT command during DDR3 memory initialization. It also issues ZQCS command each time the EMIF_SDRAM_OUTPUT_IMPEDANCE_CALIBRATION_CONFIG[15:0] ZQ_REFINTERVAL bit field expires. In other words, the ZQ_REFINTERVAL defines the interval between two ZQCS commands. When ZQCS command is issued, the EMIF waits and blocks any other command for EMIF_SDRAM_TIMING_3[20:15] ZQ_ZQCS + 1 number of DDR clock cycles.
If the EMIF_SDRAM_OUTPUT_IMPEDANCE_CALIBRATION_CONFIG[28] ZQ_SFEXITEN bit field is set to 0x1, the EMIF issues ZQCL command every time it exits self-refresh, active power-down and precharge power-down modes. When ZQCL command is issued, the EMIF waits and blocks any other command for (EMIF_SDRAM_OUTPUT_IMPEDANCE_CALIBRATION_CONFIG[17:16] ZQ_ZQCL_MULT + 1) × (EMIF_SDRAM_TIMING_3[20:15] ZQ_ZQCS + 1) number of DDR clock cycles.
The ZQINIT is a non periodic command issued only once during DDR3 initialization as opposed to the ZQCL and ZQCS calibration commands which are issued by the EMIF periodically at regular intervals.