7- 34 M68040 USER’S MANUAL MOTOROLA
generates the vector number, which is the sum of the interrupt priority level plus 24 ($18).
There are seven distinct autovectors that can be used, corresponding to the seven levels
of interrupts available with IPL2–IPL0 signals. Figure 7-23 illustrates a functional timing
diagram for an autovector operation.
Figure 7-23. Autovector Interrupt Acknowledge Bus Cycle Timing
18.104.22.168 SPURIOUS INTERRUPT ACKNOWLEDGE BUS CYCLE. When a device does
not respond to an interrupt acknowledge bus cycle with TA, or AVEC and TA , the external
logic typically returns the transfer error acknowledge signal (TEA). In this case, the
M68040 automatically generates the spurious interrupt vector number 24 ($18) instead of
the interrupt vector number. If TA and TEA are both asserted, the processor retries the