/** Project name : Clock; Data : 2020 April 2; Function : A clock for millisecond precision, 4 keys modify Clock parameter; KEY0 is pause key under running mode and add one under settings mode KEY1 is right key under settings mode KEY2 is lift key under settings mode KEY3 is set key Hardware : DE2-115; Development environment : Quartus II 15.0; FPGA type: EP4CE115F29C7; System frequency : 50MHz; Company : Author : Hardware simulation : Modification record : */