MOTOROLA
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SECTION 5: INTERRUPTS
MC68HC05V7 Specification Rev. 1.0
5.5.1.4
IRQF - IRQ Interrupt Request
The IRQF flag bit indicates that an IRQ request is pending. Writing to the IRQF flag bit will
have no effect on it. The IRQF flag bit is cleared when the IRQ vector is fetched prior to the
service routine being entered. The IRQF flag bit can also be cleared by writing a logic one
to the IRQA acknowledge bit to clear the IRQ latch. In this way any additional IRQF flag bit
that is set while in the service routine can be ignored by clearing the IRQF flag bit before
exiting the service routine. If the additional IRQF flag bit is not cleared in the IRQ service
routine and the IRQE enable bit remains set, the CPU will re-enter the IRQ interrupt
sequence continuously until either the IRQF flag bit or the IRQE enable bit is clear. The IRQ
latch is cleared by reset. This flag can be set only when the IRQE enable is set.
5.5.1.5
IRQPCE - Port C IRQ Interrupt Enable
The IRQPCE bit controls whether the IRQPCF flag bit can or cannot initiate an IRQ interrupt
sequence. If the IRQPCE enable bit is set the IRQPCF flag bit can generate an interrupt
sequence. If the IRQPCE enable bit is cleared the IRQPCF flag bit cannot generate an
interrupt sequence. Reset clears the IRQPCE enable bit, thereby disabling Port C IRQ
interrupts. In addition, reset also sets the I-bit, which masks all interrupt sources. Execution
of the STOP or WAIT instructions does not effect the IRQPCE bit.
5.5.1.6
IRQPAE - Port A IRQ Interrupt Enable
The IRQPAE bit controls whether the IRQPAF flag bit can or cannot initiate an IRQ interrupt
sequence. If the IRQPAE enable bit is set the IRQPAF flag bit can generate an interrupt
sequence. If the IRQPAE enable bit is cleared the IRQPAF flag bit cannot generate an
interrupt sequence. Reset clears the IRQPAE enable bit, thereby disabling Port A IRQ
interrupts. In addition, reset also sets the I-bit, which masks all interrupt sources. Execution
of the STOP or WAIT instructions does not effect the IRQPAE bit.
NOTE:
The IRQPAE and IRQPCE mask bits must be set prior to entering STOP
or WAIT modes if Port IRQ interrupts are to be enabled.
5.5.1.7
IRQE - IRQ Interrupt Enable
The IRQE bit controls whether the IRQF flag bit can or cannot initiate an IRQ interrupt
sequence. If the IRQE enable bit is set the IRQF flag bit can generate an interrupt
sequence. If the IRQE enable bit is cleared the IRQF flag bit cannot bet set and therefor
cannot generate an interrupt sequence. Reset sets the IRQE enable bit, thereby enabling
IRQ interrupts once the I-bit is cleared. Execution of the STOP or WAIT instructions causes
the IRQE bit to be set in order to allow the external IRQ to exit these modes. In addition,
reset also sets the I-bit, which masks all interrupt sources.
5.5.2
If the interrupt mask bit (I bit) of the CCR is set, all maskable interrupts (internal and
external) are disabled. Clearing the I bit enables interrupts. The interrupt request is latched
immediately following the falling edge of the IRQ source. It is then synchronized internally
External Interrupt Timing
F
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