This project is used as an electronic private exchange. It has two telephones, which have the intercom facility, and they can be connected to the telephone line. All the functions are controlled by the 8-bit microcontroller AT89C2051 which has an Pro

avr单片机 定义矩阵键盘上的10个数字按键，将每个数字键与特定的音调相结合起来，-avr microcontroller definition of matrix 10 digits on the keyboard keys, each number key and the combination of specific tone up

三个功能键，当上电后，系统显示提示符P。按下k1后，系统开始正常运行，此时按其它键均无效当再按下k1后，进入调秒状态，按k2加1,按k3减1,再按一下k1进入调分状态，再按一下，进入调时，再按一下，进入正常的运行状态在调整状态下，当调整该位时，该位会闪烁-Three function keys, when the power on, the system displays the prompt P. After pressing k1, the system starts running, t

1.所有已知错误除大数乘法外皆解决 2.添加按键音 3.解决老版本缓冲区清空问题 4.添加类似windows计算器的/=功能（即自身作为第二个操作数） 5.目前小数仅保留4位以内-1. All known bugs are solved outside except multiply large numbers 2. Add the key tone 3. Solve the problem the old version of the buffer empty 4.