MC68HC705C9ACFN datasheet(47/157 Pages) FREESCALE

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General Release Specification

Non-Maskable Software Interrupt (SWI)

MC68HC705C9A — Rev. 2.0

Interrupts

4.3 Non-Maskable Software Interrupt (SWI)

The SWI is an executable instruction and a non-maskable interrupt: It is

executed regardless of the state of the I bit in the CCR. If the I bit is zero

(interrupts enabled), SWI executes after interrupts which were pending

when the SWI was fetched, but before interrupts generated after the SWI

was fetched. The interrupt service routine address is specified by the

contents of memory locations $3FFC and $3FFD.

4.4 External Interrupt (IRQ or Port B)

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

IRQ. It is then synchronized internally and serviced as specified by the

contents of $3FFA and $3FFB.

When any of the port B pullups are enabled, each pin becomes an

additional external interrupt source which is executed identically to the

IRQ pin. Port B interrupts follow the same edge/edge-level selection as

the IRQ pin. The branch instructions BIL and BIH also respond to the

port B interrupts in the same way as the IRQ pin. See 7.4 Port B.

Either a level-sensitive and edge-sensitive trigger or an

edge-sensitive-only trigger operation is selectable. In MC68HC05C9A

mode, the sensitivity is software- controlled by the IRQ bit in the C9A

option register ($3FDF). In the MC68HC05C12A mode, the sensitivity is

determined by the C12IRQ bit in the C12 mask option register ($3FF1).

NOTE:

The internal interrupt latch is cleared in the first part of the interrupt

service routine; therefore, one external interrupt pulse can be latched

and serviced as soon as the I bit is cleared.

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MC68HC705C9ACFN Datasheet(PDF) 47 Page - Freescale Semiconductor, Inc