
External Interrupt Module (IRQ)
MC68HC908AZ60 — Rev 2.0
External Interrupt Module (IRQ)
Functional Description
A logic 0 applied to the external interrupt pin can latch a CPU interrupt
request. Figure 1 shows the structure of the IRQ module.
Interrupt signals on the IRQ/VPP pin are latched into the IRQ latch. An
interrupt latch remains set until one of the following actions occurs:
Vector fetch — A vector fetch automatically generates an interrupt
acknowledge signal that clears the latch that caused the vector
fetch.
Software clear — Software can clear an interrupt latch by writing
to the appropriate acknowledge bit in the interrupt status and
control register (ISCR). Writing a logic 1 to the ACK1 bit clears the
IRQ latch.
Reset — A reset automatically clears both interrupt latches.
Figure 1. IRQ Block Diagram
ACK1
IMASK1
DQ
CK
CLR
IRQ
HIGH
INTERRUPT
TO MODE
SELECT
LOGIC
IRQ
LATCH
REQUEST
IRQ/VPP
V
DD
MODE1
VOLTAGE
DETECT
SYNCHRO-
NIZER
IRQF
TO CPU FOR
BIL/BIH
INSTRUCTIONS
VECTOR
FETCH
DECODER
INTERNAL
ADDRESS
BUS
2-irq
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Freescale Semiconductor, Inc.
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