MC68HC705JP7 Datasheet, PDF(57/242 Page) Motorola, Inc – HCMOS Microcontroller Unit

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MC68HC705JP7 Datasheet, PDF (57/242 Pages) Motorola, Inc – HCMOS Microcontroller Unit

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Freescale Semiconductor, Inc.

Interrupts

External Interrupts

NOTE:

The response of the IRQ/VPP pin can be affected if the external interrupt

capability of the PA0 through PA3 pins is enabled. If the port A pins are

enabled as external interrupts, then any high level on a PA0âPA3 pin will

cause the IRQ changes and state to be ignored until all of the PA0âPA3

pins have returned to a low level.

4.6.2 PA0âPA3 Pins

Programming the PIRQ bit in the MOR to a logic 1 enables the PA0âPA3

pins (PA0:3) to serve as additional external interrupt sources. A rising

edge on a PA0:3 pin latches an external interrupt request. After

completing the current instruction, the CPU tests the IRQ latch. If the

IRQ latch is set, the CPU then tests the I bit in the condition code register

and the IRQE bit in the ISCR. If the I bit is clear and the IRQE bit is set,

the CPU then begins the interrupt sequence. The CPU clears the IRQ

latch while it fetches the interrupt vector, so that another external

interrupt request can be latched during the interrupt service routine. As

soon as the I bit is cleared during the return from interrupt, the CPU can

recognize the new interrupt request.

The PA0:3 pins can be edge-triggered or edge- and level-triggered.

External interrupt triggering sensitivity is selected by the LEVEL bit in the

MOR.

With the edge- and level-sensitive trigger MOR option, a rising edge or

a high level on a PA0:3 pin latches an external interrupt request. The

edge- and level-sensitive trigger MOR option allows connection to a

PA0:3 pin of multiple wired-OR interrupt sources. As long as any source

is holding the pin high, an external interrupt request is present, and the

CPU continues to execute the interrupt service routine.

With the edge-sensitive only trigger MOR option, a rising edge on a

PA0:3 pin latches an external interrupt request. A subsequent external

interrupt request can be latched only after the voltage level of the

previous interrupt signal returns to a logic 0 and then rises again to a

logic 1.

NOTE: If the port A pins are enabled as external interrupts, then a high level on

any PA0:3 pin will drive the state of the IRQ function such that the

MC68HC705JJ7 â¢ MC68HC705JP7 â REV 4

MOTOROLA

Interrupts

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