Abstract: A multi-bank testing apparatus for a synchronous DRAM, which allows all banks of the synchronous DRAM to simultaneously carry out their write and read operations in a test mode, thereby being capable of testing the entire bank in order to reduce the test time being likely to increase in accordance with an increased memory integration degree.

Abstract: An apparatus and a method for improving the stability of the transmitting frequency by using a costas loop section in a communication system of a half duplex transmitting method is disclosed, in which a receiving terminal is provided with an A/D converter, a D/A converter, a switching circuit, and a central processing unit, and thus, during a data transmission, a reference frequency is extracted through the costas loop section without installing a separate reference frequency extracting facility, thereby improving the stability of the transmitting frequency. In the conventional technique, in forming a reference frequency for a transmitting frequency, additional devices such as a pilot signal detector, a transmission reference frequency oscillator and the like are required, with the result that the cost for establishing the system becomes high, and that too much man hours and too many additional components are required.