Motorola MC68020 - Assertion of IPEND (MC68020 Only)

MOTOROLA M68020 USER’S MANUAL 6- 15
The MC68020 asserts IPEND (note that IPEND is not implemented in the MC68EC020)
when it makes an interrupt request pending. Figure 6-4 shows the assertion of
IPEND
relative to the assertion of an interrupt level on IPL2–IPL0. IPEND signals to external
devices that an interrupt exception will be taken at an upcoming instruction boundary
(following any higher priority exception). The state of the
IPEND signal is internally
checked by the processor once per instruction, independently of bus operation. In
addition, it is checked during the second instruction prefetch associated with exception
processing.
Figure 6-5 is a flowchart of the interrupt recognition and associated exception processing
sequence.
CLK
IPL2–IPL0
IPEND
COMPARE REQUEST
WITH MASK IN S
R
ASSERT IPEND
IPL2–IPL0 RECOGNIZED
IPL2–IPL0 SYNCHRONIZED
Figure 6-4. Assertion of IPEND (MC68020 Only)