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8259A与MCS-51单片机接口技术的关键在于当CPU响应中断时如何产生三个(?)脉冲信号,以便可从8259A直接获得相应的中断服务程序的入口地址,而后转去执行中断服务程序。下图表示了8031单片机与两片8259A相连接的一种硬件接口方法。由图可见,373作为P_0口的输出锁存器,地址A_3低电平有效信号与(?)有效信号相“或”后可产生(?)脉冲信号。8259A的中断请求信号INT经非门后接向8031的(?)引脚,故编程时应从0003H单元开始存放一条转移指令(如AJMP 0101H),再从0101H单元开
The key to the 8259A’s interfacing with the MCS-51 microcontroller is how to generate three (?) Pulse signals when the CPU responds to an interrupt so that the 8259A can directly access the corresponding interrupt service routine’s entry address and then execute the interrupt service routine. The figure below shows a 8031 MCU with two 8259A connected to a hardware interface. Can be seen from the figure, 373 P_0 port as the output latch, address A_3 active low signal and (?) Valid signal phase “or” can generate (?) Pulse signal. The interrupt request signal INT of 8259A is connected to the (?) Pin of the 8031 through the NOT gate. Therefore, a branch instruction (such as AJMP 0101H) should be stored in the 0003H unit during programming and then the 0101H unit ON