EXTERNAL INTERRUPTS
Chapter 2 External Interrupts
MCU-AN -300203-E-V17
- 6 -
© Fujitsu Microelectronics Europe GmbH
2 External Interrupts
THE BASIC FUNCTIONALITY OF THE EXTERNAL INTERRUPT MODULE
2.1 Block
Diagram
Figure 2-1 shows the internal block diagram of an External Interrupt channel.
Figure 2-1: External Interrupts Block Diagram
2.2 Connection
Diagram
Figure 2-2 shows the connection diagram depicting how the external interrupt pin INTn is
interfaced to the external circuitry.
The pull up resistor R is connected to limit the current when the key is pressed. The
capacitor (hardware debounce) circuit shown with the dotted line is optional and is used to
eliminate the bouncing of the switch. The RC time constant needs to be chosen according to
the bouncing time or debounce delay of the switch. If such arrangement is not used then the
bouncing needs to be taken care in the software and also vice a versa.
Here the INTn needs to be configured to detect a falling edge.
Figure 2-2: External Interrupts Connection Diagram
C
R
Vcc
MCU
INTn
Pin INTn
Interrupt
Request
Edge
Detection
Circuit
MCU
