FUJITSU MB91F109 FR30 - Manual (Page 241)

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6.6 External Interrupt Request Levels
6.6 External Interrupt Request Levels
When an edge is selected for the interrupt request mode, a pulse width of at least three
machine cycles (peripheral clock machine cycles) is required to detect an edge.
When a level is selected for the interrupt request mode, an external request that has
been input may be canceled later, though the request issued to the interrupt controller
remains active because an interrupt cause hold circuit exists inside.
The interrupt request register must be cleared to cancel the request issued to the
interrupt controller.
■ External Interrupt Request Levels
Figure 6.6-1 shows how the interrupt cause hold circuit is cleared when a level is selected for
the interrupt request mode. Figure 6.6-2 shows the input of an interrupt cause in interrupt
enable mode and a request issued to the interrupt controller.
Figure 6.6-1 Clearing the Interrupt Cause Hold Circuit at Level Setting for the Interrupt Request Mode
Figure 6.6-2 Input of an Interrupt Cause in Interrupt Enable Mode and a Request Issued to the Interrupt
Controller
Level
detection
Input of interrupt Cause F/F
(cause hold circuit)
The cause is held until the flip-flop is cleared.
Enable gate To the interrupt
controller
H level
Interrupt request to
the interrupt controller
Input of interrupt
Clearing the interrupt cause flip-flop deactivates the signal.