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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.
C1 C2
A31–A0
BCLK
BYTE
SIZ1
TT1, TT0
TM2–TM0
D31–D0
UPA1, UPA0
CIOUT
TS
TIP
TA
R/W
SIZ0
INTERRUPT
ACKNOWLEDGE 
AUTOVECTORED
INTERRUPT LEVEL
AVEC
C1 C2
WRITE STACK
Figure 7-23. Autovector Interrupt Acknowledge Bus Cycle Timing
7.5.1.3 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
cycle.
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