This paper introduces simply the composition and function of the centralized manageable message accounting system of public telephone. The system consists of the centralized management center and the centralized manageable message accounting devices. Between the center and the devices

the duplex communication links are created through the public switched telephone network

thus the remote management for the devices is realized. It describes the structure of the message accounting device. We design the special interface circuit between the message accounting device and the telephone wire. A piece of completely theoretical basis is presented in order to resolve the software design emphasis of the accounting device

such as the procedure design of off-hook and on hook and dialing pulse recognition.