InterruptsInterrupts are organized into 256 vectors termed INT-00 through INT-FF. The first sixteen (INT-00 through INT-0F) are for CPU internal use; all others (INT-10 to INT-FF) are available to peripherals.
Interrupt vectors points to consecutive locations in the very first block of the addressable space. Each vector takes two consecutive addresses, thus INT-00 points to 0x00000, INT-01 points to 0x00002 and so on. INT-FF points to 0x001fe.
When interrupted, the CPU fetches the corresponding vectored address. What is expected to be there is a branch instruction to the actual ISR.
INT-00 is the computer's clock tic raised at 1 ms intervals. A multitasking operating system can make use of INT-0 to define processes time-slices among other uses.
INT-01 through INT-FF are used by the CPU to generate exceptions. Software code is allowed to raise interrupts within this range by using interrupt instructions.
All interrupts are maskable. Not masked interrupts can be served in a nested fashion according to interrupt priority.
Queuing interrupt requests is the job of the Operating System. The CPU limits itself to service interrupts in the simple way we just described.
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