
GENERAL RELEASE SPECIFICATION
June 11, 1997
MOTOROLA
INTERRUPTS
MC68HC05CL48
4-6
REV 2.0
4.3.2 External Interrupts (IRQ0, IRQ1, IRQ2, KBI[3:7])
4.3.2.1
IRQ0, IRQ1, IRQ2
IRQ0, IRQ1, IRQ2 interrupt function is associated with PTA[0:2]. IRQ[0:2]
interrupts behave similar to IRQ except these are edge-triggered only. IRQ0 and
IRQ1 are both negative-edge triggered only and IRQ2 can be triggered on both
rising and falling edges. To enable this function, IRQE0, IRQE1 and IRQE2 bit of
the external interrupt control register (EXICR $1D) should be set rst. When an
appropriate edge occurring at the IRQ0, IRQ1 or IRQ2 pin and the interrupt mask
bit of the condition code register is cleared will cause an external interrupt to
occur. If the MCU has nished with the service routine, but the external interrupt
pin has not resumed backed to high, no further interrupt will be generated. If the
appropriate triggering edge occurs when the interrupt mask bit is set, the interrupt
signal will be latched, and interrupt will occur as soon as the interrupt mask bit is
cleared. The latch for IRQ0, IRQ1 and IRQ2 are cleared by reset or cleared by
writing a ‘0’ to the IRQF0, IRQF1 and IRQF2 bit in the external interrupt status
register ($1E EXISR) in the service routine.
The interrupt service routine is specied by the contents of the memory locations
$FFF2 and $FFF3.
To prevent unwanted interrupts generated on RQ0, IRQ1 pins. A logic ‘1’ should
be written to these pins before setting their corresponding interrupt enable bits.
Likewise, A logic ‘1’ should be written to IRQ2 pin prior to setting the IRQ2
interrupt enable bit.
4.3.2.2
Keyboard Interrupts
Keyboard Interrupt function is associated with PTA[3:7]. The keyboard interrupt
function is enabled by setting the individual interrupt enable bits KBE[3:7]
(bits[3:7] of EXICR at $001D). When the KBE bit is set, the corresponding Port A
pin will be congured as an input pin, regardless of the DDR setting, and a 100k
ohm pull-up resistor is connected to the pin, as shown in Figure 4-3. When a high
to low transition is sensed on the pin, a keyboard interrupt will be generated,
provided the I-bit in the CCR is cleared.
The interrupt signal is latched, and it should be cleared by writing a ‘0’ to the
corresponding KBIF bit in the external interrupt status register ($1E EXISR) in the
interrupt service routine. This should be cleared after the key is debounced, or
unwanted keyboard interrupt signal will be generated.
The Keyboard Interrupt is negative-edge sensitive only, and the interrupt service
routine is specied by the contents of the memory locations $FFF2 and $FFF3.