Notes On Using The External Interrupt Functions - Fujitsu MB96300 series Hardware Manual

CHAPTER 17 EXTERNAL INTERRUPTS
17.3

Notes on using the External Interrupt functions

The following points must be considered to use the External Interrupt function.
• Conditions on the behavior of external circuit for use of DMA
• Clearing interrupt flag
• External interrupt request level
■ Conditions on the behavior of external circuit for use of DMA
• An external circuit which uses DMA must be able to inactivate the request signal when the requested
DMA transfer is performed. For the correct usage of external interrupts to start DMA transfers please
refer to application note MCU-AN-390208-e.
■ Clearing interrupt flag
• When it is used as an external interrupt the interrupt flag must be cleared within the interrupt service
routine. Otherwise the same service is performed again after the completion of the first interrupt service.
• When level detection is specified as the event input, the interrupt flag is set again even after it is cleared as
long as the active level is kept at the input pin. In this case, the external cause of the request should be
cleared or the interrupt enable bit should be cleared.
■ External interrupt request level
• When edge detection is specified as the event input, the pulse of the input signal must have a minimum
width to be recognized as an input edge and not be filtered by the noise filter. See datasheet of the specific
device for the minimum pulse width length.
• When level detection is specified as the event input, the interrupt flag keeps active status once the
specified level is input even after the input signal changes to the inactive level as shown in Figure 17.3-2
"Interrupt cause and interrupt request to the interrupt controller while interrupts are enabled". In order to
clear the request, the interrupt flag must be cleared.
Figure 17.3-1 Clearing interrupt cause register upon level set
Level detection Interrupt cause
Figure 17.3-2 Interrupt cause and interrupt request to the interrupt controller while interrupts are enabled
Interrupt cause
Interrupt request to
the interrupt controller
432
Interrupt flag
(interrupt cause register)
The cause is kept held unless cleared.
H level
MB96300 Super Series Hardware Manual
Interrupt enable
Set inactive when the interrupt flag is cleared
To interrupt
controller