数字秒表的VHDL语言实现，由于系统定时器8253每秒中断18.2次,利用INT 1AH/00H取得中断次数(DX),得到54.945ms的定时单位。

-Digital stopwatch the VHDL language, because the system timer interrupt 18.2 times per second, 8253, made use of INT 1AH/00H interrupt number (DX), by 54.945ms timing unit.