说明：  脉冲按键电话按键显示器：设计一个具有7位显示的电话按键显示器，显示器应能正确反映按键数字，显示器显示从低位向高位前移，逐位显示按键数字，最低位为当前显示位。 2．七位数字输入完毕后，电话接通，扬声器发出“嘟——嘟”接通声响，直到有接听信号输入。 3．若一直没有接听，10秒钟后，自动挂断，显示器清除显示，扬声器停止，直到有新号码输入。
(Pulse button phone keypad display: design a seven display phone keypad displays, monitors should be able to correctly reflect the key figures, from low to high display forward, bit by bit display key figures, the lowest for the current display position. 2. After seven digital inputs, telephone connections, the speaker issued a " toot- toot" sound connected until the answering signal input. 3. If it has not been answered, 10 seconds, automatically hang up, clear display shows speaker to stop, until the new number input.)