Advance Information MC68HC908MR16/MC68HC908MR32 — Rev. 4.0
330 External Interrupt (IRQ) MOTOROLA
External Interrupt (IRQ)
17.4 Functional Description
A logic 0 applied to any of the external interrupt pins can latch a CPU
interrupt request. Figure 17-1 shows the structure of the IRQ module.
Interrupt signals on the IRQ pin are latched into the IRQ1 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
IRQ1 latch.
Reset — A reset automatically clears both interrupt latches.
Figure 17-1. IRQ Module Block Diagram
Addr. Register Name Bit 7 6 5 4 3 2 1 Bit 0
$003F IRQ Status/Control Register
(ISCR)
See page 334.
Read: 0 0 0 0 IRQF 0IMASK1 MODE1
Write: R R R R ACK1
Reset:00000000
R= Reserved
Figure 17-2. IRQ I/O Register Summary
ACK1
IMASK1
DQ
CK
CLR IRQ
HIGH
INTERRUPT
TO MODE
SELECT
LOGIC
IRQ
LATCH
REQUEST
IRQ
VDD
MODE1
VOLTAGE
DETECT
SYNCHRO-
NIZER