Servicing Personal Computers, 3rd Edition

268 Servicing Personal Computers

Group 0 exceptions cause the currently executing instruction to be aborted and this allows

exception processing to start within two clock cycles. Response to a Group 0 exception is thus

virtually immediate.

Group 1 exceptions allow the execution of the current instruction to be completed.

Thereafter, exception processing begins before the next instruction. Note that privilege

violations and illegal instructions are detected when they are the next instruction to be

executed.

Since more than one exception may arise at the same time, some mechanism for

determining exception priority is required. This mechanism