The ZQ calibration command can calibrate the DRAM's output drivers (Ron) and ODT values (Rtt) over process, voltage, and temperature when a dedicated 240 ohm (±1 percent) resistor is connected from the DRAM's ZQ pin to ground. In DDR3, two different calibration commands exist: ZQ calibration long (ZQCL) and ZQ calibration short (ZQCS). ZQCL is normally used during power-up initialization and reset sequences, but may be issued at any time by the controller, depending on the system environment. ZQCS is used to perform periodic calibrations to account for small voltage and temperature variations; it requires a smaller timing window to complete.