MC68LC040RC25A Datasheet, PDF (173/442 Pages) Freescale Semiconductor, Inc – M68040 Users Manual

Freescale Semiconductor, Inc.
The M68040 takes an interrupt exception for a pending interrupt within one instruction
boundary after processing any other pending exception with a higher priority. Thus, the
M68040 executes at least one instruction in an interrupt exception handler before
recognizing another interrupt request. The following paragraphs describe the various kinds
of interrupt acknowledge bus cycles that can be executed as part of interrupt exception
processing. Table 7-4 provides a summary of the possible interrupt acknowledge
terminations and the exception processing results.
Table 7-4. Interrupt Acknowledge Termination Summary
TA
High
High
Low
Low
Low
TEA
High
Low
High
High
Low
AVEC
Termination Condition
Don’t Care Insert Waits
Don’t Care Take Spurious Interrupt Exception
High
Latch Vector Number on D7–D0 and Take Interrupt
Exception
Low Take Autovectored Interrupt Exception
Don’t Care Retry Interrupt Acknowledge Cycle
7.5.1.1 INTERRUPT ACKNOWLEDGE BUS CYCLE (TERMINATED NORMALLY).
When the M68040 processes an interrupt exception, it performs an interrupt acknowledge
bus cycle to obtain the vector number that contains the starting location of the interrupt
exception handler. Some interrupting devices have programmable vector registers that
contain the interrupt vectors for the exception handlers they use. Other interrupting
conditions or devices cannot supply a vector number and use the autovector bus cycle
described in 7.5.1.2 Autovector Interrupt Acknowledge Bus Cycle.
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M68040 USER’S MANUAL
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