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■ External interrupt request level
•
If edge request has been selected for the request level, at least a pulse width of three
machine cycles is required for detecting edge.
•
If level setting has been selected for the request input level, note that an external request
that has been input remains active with respect to the interrupt controller even if it is later
withdrawn, since the interrupt controller contains an internal source retention circuit. To
withdraw a request with respect to the interrupt controller, the source retention circuit must
be cleared.
Figure 16.5-1 Clearing the source retention circuit when setting the request level
Interrupt
Level detection
source
Figure 16.5-2 Interrupt sources and interrupt requests to the interrupt controller when interrupts are
Interrupt source
Interrupt request to
interrupt controller
Note:
Edge detection cannot be used to return from watch mode.
Source F/F
(source retention
circuit)
Source is retained
until cleared
enabled
"H" level
Turned to inactive by clearing source F/F
CHAPTER 16 DTP/EXTERNAL INTERRUPTS
Enable gate
To interrupt
controller
351
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