8- 14 M68040 USER’S MANUAL MOTOROLA
EXTERNAL
IPL2–IPL0
INTERRUPT PRIORITY
MASK (I2–I0) ACTION
LEVEL 6 EXAMPLE
(INITIAL CONDITIONS)
100 ($3) 101 ($5)
(LEVEL COMPARISON)IF 001 ($6) THEN 110 ($6) AND LEVEL 6 INTERRUPT
IF 100 ($3) AND STILL 110 ($6) THEN NO ACTION
IF 001 ($6) AND STILL 110 ($6) THEN NO ACTION
IF STILL 001 ($6) AND RTE SO THAT 101 ($5) THEN LEVEL 6 INTERRUPT (LEVEL COMPARISON)
(TRANSITION)
(TRANSITION)
(INITIAL CONDITIONS)
100 ($3) 101 ($5)
IF 000 ($7) THEN 111 ($7) AND LEVEL 7 INTERRUPT
IF 100 ($3) AND STILL 111 ($7) THEN NO ACTION
IF 000 ($7) AND STILL 111 ($7) THEN NO ACTION
IF STILL 000 ($7) AND RTE SO THAT 101 ($5) THEN LEVEL 7 INTERRUPT (LEVEL COMPARISON)
LEVEL 7 EXAMPLE
Figure 8-3. Interrupt Recognition Examples
Note that a mask value of 6 and a mask value of 7 both inhibit request levels of 1–6 from
being recognized. In addition, neither masks a transition to an interrupt request level of 7.
The only difference between mask values of 6 and 7 occurs when the interrupt request
level is 7 and the mask value is 7. If the mask value is lowered to 6, a second level 7
interrupt is recognized.
External circuitry can chain or otherwise merge signals from devices at each level,
allowing an unlimited number of devices to interrupt the processor. When several devices
are connected to the same interrupt level, each device should hold its interrupt priority
level constant until its corresponding interrupt acknowledge bus cycle ensures that all
requests are processed. Refer to Section 7 Bus Operation for details on the interrupt
acknowledge cycle.
