一、6502对中断的处理 6502和一般较高档的八位微处理器一样,有不可屏蔽中断(NMI-Non MaskableInterrupt)和可屏蔽中断(Maskable Interrupt)两种中断方式。前者是通过NMI信号线上出现下跳沿而完成中断请求的;后者则为IRQ=0时进行中断请求。对于前者,CPU总是无条件地响应:对于后者,只有在状态寄存器P中的中断屏蔽位(I位)为0时才能响应。 此外,6502的BRK指令的作用正相当于内部中断请求。CPU执行它时,与CPU对IRQ响应后所执行的功能是基本相同的,因此,让我们先看一下执行BRK的过程: First, the 6502 interrupt handling 6502 and general higher-end eight microprocessors, there are NMI (Non Maskable Interrupt) and maskable interrupt (Maskable Interrupt) two interrupts. The former completes the interrupt request by the occurrence of the next hop on the NMI signal line. The latter interrupt request is generated when IRQ = 0. For the former, the CPU always responds unconditionally: In the latter case, the interrupt can only be serviced if the interrupt mask bit (I bit) in the status register P is zero. In addition, the effect of the 6502 BRK instruction is equivalent to an internal interrupt request. When the CPU executes it, the functions performed by the CPU after responding to the IRQ are basically the same, so let’s take a look at the process of executing a BRK: