MC68030 Datasheet, PDF (277/602 Pages) Motorola, Inc – ENHANCED 32-BIT MICROPROCESSOR

Exception Processing
ENTRY
A19-A16 $0
A4-A2 BREAKPOINT NUMBER
INITIATE READ BUS CYCLE
DSACKx OR STERM
CYCLE TERMINATED WITH
BERR
PIPE STAGE D INSTRUCTION WORD ON DATA BUS
EXECUTE INSTRUCTION WORD
TAKE ILLEGAL INSTRUCTION
EXCEPTION
EXIT
Figure 8-7. Breakpoint Instruction Flowchart
8.1.12 Multiple Exceptions
When several exceptions occur simultaneously, they are processed according to a fixed
priority. Table 8-5 lists the exceptions, grouped by characteristics. Each group has a priority
from 0-4. Priority 0 has the highest priority.
As soon as the MC68030 has completed exception processing for a condition when another
exception is pending, it begins exception processing for the pending exception instead of
executing the exception handler for the original exception condition. Also, whenever a bus
error or address error occurs, its exception processing takes precedence over lower priority
exceptions and occurs immediately. For example, if a bus error occurs during the exception
processing for a trace condition, the system processes the bus error and executes its
handler before completing the trace exception processing. However, most exceptions
cannot occur during exception processing, and very few combinations of the exceptions
shown in Table 8-5 can be pending simultaneously.
MOTOROLA
MC68030 USER’S MANUAL
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