MC68HC908KX8 Datasheet, PDF (167/310 Pages) Motorola, Inc – Microcontrollers

External Interrupt (IRQ)
IRQ1 Pin
When an interrupt pin is edge-triggered only, the interrupt latch remains
set until a vector fetch, software clear, or reset occurs.
When an interrupt pin is both falling-edge and low-level triggered, the
interrupt latch remains set until both of these occur:
• Vector fetch or software clear
• Return of the interrupt pin to logic 1
The vector fetch or software clear may occur before or after the interrupt
pin returns to logic 1. As long as the pin is low, the interrupt request
remains pending. A reset will clear the latch and the MODE1 control bit,
thereby clearing the interrupt even if the pin stays low.
When set, the IMASK1 bit in the ISCR masks all external interrupt
requests. A latched interrupt request is not presented to the interrupt
priority logic unless the IMASK1 bit is clear.
NOTE: The interrupt mask (I) in the condition code register (CCR) masks all
interrupt requests, including external interrupt requests.
12.5 IRQ1 Pin
A logic 0 on the IRQ1 pin can latch an interrupt request into the IRQ1
latch. A vector fetch, software clear, or reset clears the IRQ1 latch.
If the MODE1 bit is set, the IRQ1 pin is both falling-edge sensitive and
low-level sensitive. With MODE1 set, both of the following actions must
occur to clear the IRQ1 latch:
• Vector fetch or software clear — A vector fetch generates an
interrupt acknowledge signal to clear the latch. Software may
generate the interrupt acknowledge signal by writing a logic 1 to
the ACK1 bit in the interrupt status and control register (ISCR).
The ACK1 bit is useful in applications that poll the IRQ1 pin and
require software to clear the IRQ1 latch. Writing to the ACK1 bit
can also prevent spurious interrupts due to noise. Setting ACK1
does not affect subsequent transitions on the IRQ1 pin. A falling
edge on the IRQ1 pin that occurs after writing to the ACK1 bit
MC68HC908KX8 • MC68HC908KX2 • MC68HC08KX8 — Rev. 1.0
MOTOROLA
External Interrupt (IRQ)
Technical Data
167