MC68030 Datasheet, PDF (269/602 Pages) Motorola, Inc – ENHANCED 32-BIT MICROPROCESSOR

Exception Processing
The peripheral device uses the active-low interrupt priority level signals (IPL0–IPL2) to
signal an interrupt condition to the processor and to specify the priority of that condition. The
three signals encode a value of zero through seven (IPL0 is the least significant bit). High
levels on all three signals correspond to no interrupt requested (level 0) and low levels on
IPL0–IPL2 correspond to interrupt request level 7. Values 1-7 specify one of seven levels of
prioritized interrupts; level seven has the highest priority. External circuitry can chain or
otherwise merge signals from devices at each level, allowing an unlimited number of devices
to interrupt the processor.
The IPL0–IPL2 interrupt signals must maintain the interrupt request level until the MC68030
acknowledges the interrupt to guarantee that the interrupt is recognized. The MC68030
continuously samples the IPL0–IPL2 signals on consecutive falling edges of the processor
clock to synchronize and debounce these signals. An interrupt request that is the same for
two consecutive falling clock edges is considered a valid input. Although the protocol
requires that the request remain until the processor runs an interrupt acknowledge cycle for
that interrupt value, an interrupt request that is held for as short a period as two clock cycles
could be recognized.
The status register of the MC68030 contains an interrupt priority mask (I2, I1, I0, bits 10-8).
The value in the interrupt mask is the highest priority level that the processor ignores. When
an interrupt request has a priority higher than the value in the mask, the processor makes
the request a pending interrupt. Figure 8-2 is a flowchart of the procedure for making an
interrupt pending.
RESET
OTHERWISE
SAMPLE AND SYNCH
IPL2-IPL0
(COMPARE INTERRUPT LEVEL
WITH STATUS REGISTER MASK)
INTERRUPT LEVEL > I2-I0,
OR TRANSITION ON LEVEL 7
ASSERT IPEND
Figure 8-2. Interrupt Pending Procedure
MOTOROLA
MC68030 USER’S MANUAL
8-15