Explanation Of External Interrupt Circuit Operations And Setup Procedure Example - Fujitsu F2MC-8FX Hardware Manual

18.6 Explanation of External Interrupt Circuit Operations and
Setup Procedure Example
This section describes the operation of the external interrupt circuit.
Operation of External Interrupt Circuit
When the polarity of an edge of a signal inputted from one of the external interrupt pins (INT0, 1) matches
the polarity of the edge selected by the external interrupt control register (EIC: SL00 to SL11), the
corresponding external interrupt request flag bit (EIC: EIR0, EIR1) is set to "1" and the interrupt request is
generated.
Always set the interrupt enable bit to "0" when not using an external interrupt to recover from a standby
mode.
When setting the edge polarity select bit (SL), set the interrupt request enable bit (EIE) to "0" to prevent the
interrupt request from being generated accidentally. Also clear the interrupt request flag bit (EIR) to "0"
after changing the edge polarity.
Figure 18.6-1 shows the operation for setting the INT0 pin as an external interrupt input.
Input waveform
to INT0 pin
EIR0 bit
EIE0 bit
SL01 bit
SL00 bit
IRQ
Setup Procedure Example
The external interrupt circuit is set up in the following procedure:
Initial setup
1) Set the interrupt level. (ILR0, ILR5)
2) Select the edge polarity. (EIC:SL01, SL00)
3) Enable interrupt requests. (EIC:EIE0 = 1)
Figure 18.6-1 Operation of External Interrupt
Cleared by
program
No edge Rising edge
detection
CHAPTER 18 EXTERNAL INTERRUPT CIRCUIT
Interrupt request flag bit cleared
by program
Falling edge Both edges
311