FOXBORO P0926CP ZCP270控制处理器
VMIVME-7750上的中断硬件实现是围绕PC架构构建的计算机的标准，PC架构是从IBM PC/XT演变而来的。在IBM PC/XT计算机中，仅存在八条中断请求线，在PIC处编号从IRQ0到IRQ7。IBM PC/AT计算机通过将第二个从属PIC级联到原始主PIC中，又增加了八条IRQx线，编号为IRQ8到IRQ15。主PIC处的IRQ2作为从PIC的级联输入。该架构如第47页图2-1所示。为了保持与PC/XT系统的向后兼容性，IBM选择在从属PIC上使用新的IRQ9输入作为PC/XT扩展总线上的旧IRQ2中断线。因此，在AT系统中，IRQ9中断线连接到AT扩展总线（或ISA总线）上的旧IRQ2引脚（引脚B4）。
The interrupt hardware implementation on the VMIVME-7750 is standard for
computers built around the PC architecture, which evolved from the IBM PC/XT. In
the IBM PC/XT computers, only eight interrupt request lines exist, numbered from
IRQ0 to IRQ7 at the PIC. The IBM PC/AT computer added eight more IRQx lines,
numbered IRQ8 to IRQ15, by cascading a second slave PIC into the original master
PIC. IRQ2 at the master PIC was committed as the cascade input from the slave PIC.
This architecture is represented in Figure 2-1 on page 47.
To maintain backward compatibility with PC/XT systems, IBM chose to use the new
IRQ9 input on the slave PIC to operate as the old IRQ2 interrupt line on the PC/XT
Expansion Bus. Thus, in AT systems, the IRQ9 interrupt line connects to the old IRQ2
pin (pin B4) on the AT Expansion Bus (or ISA bus).
