MC68HC08XL36 Datasheet, PDF (304/362 Pages) Freescale Semiconductor, Inc – HCMOS Microcontroller Unit

IRQ
IRQ2 Pin
Freescale Semiconductor, Inc.
A logic 0 on the IRQ2 pin can latch a CPU interrupt request. A vector
fetch, software clear, or reset clears the IRQ2 CPU interrupt request.
If the MODE2 bit is set, the IRQ2 pin is both falling-edge-sensitive and
low-level-sensitive. With MODE2 set, both of the following actions must
occur to clear an IRQ2 CPU interrupt request:
• Vector fetch, software clear, or reset — A vector fetch generates
an interrupt acknowledge signal to clear the CPU interrupt
request. Software can generate the interrupt acknowledge signal
by writing a logic 1 to the ACK2 bit in the IRQ status and control
register (ISCR). The ACK2 bit is useful in applications that poll the
IRQ2 pin and require software to clear the IRQ2 CPU interrupt
request. Writing to the ACK2 bit before leaving an interrupt service
routine can also prevent spurious CPU interrupts due to noise.
Setting ACK2 does not affect subsequent transitions on the IRQ2
pin. A falling edge that occurs after writing to the ACK2 bit latches
another CPU interrupt request. If the IRQ2 mask bit, IMASK2, is
clear, the CPU loads the program counter with the vector address
at locations $FFE0 and $FFE1.
• Return of the IRQ2 pin to logic 1 — As long as the IRQ2 pin is at
logic 0, the IRQ2 CPU interrupt request remains latched.
The vector fetch, software clear, or reset and the return of the IRQ2 pin
to logic 1 can occur in any order. A reset clears the CPU interrupt request
and the MODE2 bit, clearing the CPU interrupt request even if the pin
stays low.
If the MODE2 bit is clear, the IRQ2 pin is falling-edge-sensitive only.
With MODE2 clear, a vector fetch or software clear immediately clears
the IRQ2 CPU interrupt request.
The IRQF2 bit in the ISCR register can be used to check for pending
CPU interrupts. The IRQF2 bit is not affected by the IMASK2 bit, which
makes it useful in applications where polling is preferred.
MC68HC08XL36
304
External Interrupt Module (IRQ)
For More Information On This Product,
Go to: www.freescale.com
6-intirq2_a
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