INTERRUPTS
6.10 External interrupts
6.10.2 Functions of INT
i
interrupt request bit
Figure 6.10.4 shows an INT
i
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.
INT
i
interrupt requests continuously occur while the level at pin INT
i
is the valid level
�½1
; when the level
at pin INT
i
changes from the valid level to the invalid level
�½2
before the corresponding INT
i
interrupt
request is accepted, this interrupt request is not retained. (See Figure 6.10.5.)
Valid level
�½1
: This means the level selected by the polarity select bit (bit 4 at addresses 6E
16
, 6F
16
,
FD
16
to FF
16
)
�½2
Invalid level
: This means the reversed level of “valid level”
Data bus
Level sense/Edge sense
select bit
Pin INT
i
Edge detection
circuit
Interrupt request bit
0
1
Interrupt request
Fig. 6.10.4 INT
i
Interrupt request
Interrupt request is accepted.
When the level at pin INT
i
changes
to the invalid level before the INT
i
interrupt request is accepted, this
interrupt request is not retained.
Return to main routine.
Valid
Level at pin INT
i
Invalid
Main routine
First interrupt routine
Second interrupt
routine
Third interrupt
routine
Main routine
Fig. 6.10.5 Occurrence of INT
i
interrupt request when level sense is selected
7906 Group User’s Manual Rev.2.0
6-21
RENESAS [ RENESAS TECHNOLOGY CORP ]
