7906 datasheet(100/531 Pages) RENESAS

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7906 Group User’s Manual Rev.2.0

INTERRUPTS

6-21

6.10 External interrupts

6.10.2 Functions of INTi interrupt request bit

Figure 6.10.4 shows an INTi interrupt request.

(1)

Functions when edge sense is selected

In this case, the interrupt request bit has the same function 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 occur.

(2)

Functions when level sense is selected

In this case, the interrupt request bit is ignored.

INTi interrupt requests continuously occur while the level at pin INTi is the valid level✽1; when the level

at pin INTi changes from the valid level to the invalid level✽2 before the corresponding INTi interrupt

request is accepted, this interrupt request is not retained. (See Figure 6.10.5.)

Valid level✽1: This means the level selected by the polarity select bit (bit 4 at addresses 6E16, 6F16,

FD16 to FF16)

Invalid level✽2: This means the reversed level of “valid level”

Data bus

Edge detection

circuit

Interrupt request

Interrupt request bit

Pin INTi

Level sense/Edge sense

select bit

Fig. 6.10.4 INTi Interrupt request

Fig. 6.10.5 Occurrence of INTi interrupt request when level sense is selected

When the level at pin INTi changes

to the invalid level before the INTi

interrupt request is accepted, this

interrupt request is not retained.

First interrupt routine

Level at pin INTi

Valid

Invalid

Main routine

Interrupt request is accepted.

Return to main routine.

Second interrupt

routine

Third interrupt

routine

Main routine

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