手机话费记录，通过状态机实现不同通话类型的手机话费记录功能-Their phone records, through the state machine to achieve different types of their phone call logging

用DE0开发板实现电话计费器，基本功能：可设置通话模式，能初始化话费余额，拨动开关可进入通话模式，并根据通话时间和相应通话模式扣除相应的费用。通话过程中能够通过开关切换显示通话时间和话费余额，并可暂停通话。压缩包里有详细的WORD文档的说明，包括波形仿真和DE0的引脚功能介绍。-Implemented by DE0 board telephone billing, basic function: to set the call mode, you can initiate credit bala