7721 datasheet(117/577 Pages) RENESAS

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7721 Group User’s Manual

INTERRUPTS

7–20

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7.10 External interrupts (INTi interrupt)

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7.10.1 Functions of INTi interrupt request bit

(1)

Functions when edge sense is selected

The interrupt request bit has the same functions as that of an internal interrupt. That is, when an

interrupt request occurs, the interrupt request bit is set to “1” and retains this state until the interrupt

request is accepted. When this bit is cleared to “0” by software, the interrupt request is cancelled;

when this bit is set to “1” by software, the interrupt request can be generated.

(2)

Functions when level sense is selected

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The INTi interrupt request bit is ignored.

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Interrupt requests continuously occur while the level of the INTi pin is the valid levelV1; when the INTi

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pin’s level changes from the valid level to the invalid levelV2 before the INTi interrupt request is

accepted, this interrupt request is not retained. (Refer to “Figure 7.10.4.”)

Valid levelV1: This means the level selected by the polarity select bit (bit 4 at addresses 7D16 to 7F16)

Invalid levelV2: This means the reversed level of “valid level”

INTi pin

Edge detection

circuit

Interrupt request

Level sense/Edge sense

select bit

Data bus

Interrupt request bit

“0”

“1”

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Fig. 7.10.3 INTi Interrupt request

First interrupt routine

INTi

pin level

Valid

Invalid

Main routine

Interrupt request is accepted.

Return to main routine.

Second interrupt

routine

Third interrupt

routine

Main routine

When the INTi pin’s level changes

to the invalid level before an interrupt

request is accepted, the interrupt

request is not retained.

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Fig. 7.10.4 Occurrence of INTi interrupt request when level sense is selected

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