本实验利用8253做定时器，用定时器输出的脉冲控制8259产生中断

在8259中断处理程序中，对时、分、秒进行计数，在等待中断的循

环中用LED显示时间。

8253用定时器/计数器1，8253片选接CS4，地址为0C000H。8253时钟

源CLK1接分频电路的F/64输出。分频器的Fin接4MHz时钟。8253的

GATE1接VCC。

8259中断INT0接8253的OUT1，片选接CS5，地址为0D000H。

显示电路的KEY/LED CS 接CS0，地址为08000H。-In this study, the use of 8253 to do the timer, using timer pulse output control 8259 generates an interrupt　in 8259 interrupt handler, for hours, minutes and seconds count, waiting for interruption through　ring using LED display time.　 8253 with the timer/counter 1,8253 chip select access CS4, address 0C000H. 8253 clock　source CLK1 of the F/64 then divider circuit output. Fin then 4MHz clock divider. 8253' s　GATE1 then VCC.　 8259 interrupt INT0 then 8253' s OUT1, chip select access CS5, address 0D000H.　 Display circuit of the KEY/LED CS access CS0, address 08000H.