US Patent 7853842 Semiconductor memory device with ZQ calibration

A semiconductor memory device is capable of outputting calibration codes to an external circuit. The semiconductor memory device includes a data output control unit for controlling an output of data, a calibration code output control unit for transmitting calibration codes to determine a termination resistance value, a test mode signal generating unit for generating a test mode signal which is enabled in the test mode for outputting the calibration codes, and a test mode control unit for selectively outputting the data or the calibration codes in response to the test mode signal.