ZQCL stands for ZQ calibration long. This command must be issued during the power-up and initialization sequence and requires 512 clocks to complete. After power-up and initialization, the command can be issued any time the DRAM is idle. These subsequent commands only require 246 clocks. This command is used when there is more impedance error correction required than a ZQCS can provide.
ZQCS stands for ZQ calibration short. This command can be performed any time the DRAM is idle. One ZQCS can correct a minimum of 0.5 percent impedance error and requires 64 clocks.