数字音乐盒【课程设计】1.利用I/O口产生一定频率的方波，驱动蜂鸣器，发出不同的音调，从而演奏乐曲（最少三首乐曲，每首不少于30秒） -Digital Music Box】 【Course Design 1. The use of I/O I have a certain frequency square wave to drive the buzzer, the issue of different tones, which play music (at least 3 pieces, e