FOXBORO P0926CP ZCP270控制處理器
VMIVME-7750上的中斷硬件實現是圍繞PC架構構建的計算機的標準，PC架構是從IBM PC/XT演變而來的。在IBM PC/XT計算機中，僅存在八條中斷請求線，在PIC處編號從IRQ0到IRQ7。IBM PC/AT計算機通過將第二個從屬PIC級聯到原始主PIC中，又增加了八條IRQx線，編號為IRQ8到IRQ15。主PIC處的IRQ2作為從PIC的級聯輸入。該架構如第47頁圖2-1所示。為了保持與PC/XT系統的向后兼容性，IBM選擇在從屬PIC上使用新的IRQ9輸入作為PC/XT擴展總線上的舊IRQ2中斷線。因此，在AT系統中，IRQ9中斷線連接到AT擴展總線（或ISA總線）上的舊IRQ2引腳（引腳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).
