In the recent developent of D-4 Channel Bank which is the basic PCM multiplex terminal, we utilized the one-chip microprocessor in the design of the Alarm and Trunk processing unit besides we could add more flexible functions, we simplified the logic circuits and the discrete parts. Since in Korea, we are lacking in the semiconductor technology, the microprocessor applications in the communication systems desist give us the meaningful advantages in the a aspects of economy, reliability and new technology.