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CHAPTER 11 EXTERNAL INTERRUPT CIRCUIT 2 (LEVEL)
11.5 Interrupt of External Interrupt Circuit 2
An "L" level input signal input to one of the external interrupt pins triggers external
interrupt circuit 2 to generate an interrupt.
s Interrupt During the Operation of External Interrupt Circuit 2
When an "L" level signal is input to one of the external interrupt pins for which interrupt inputs
are enabled, the external interrupt request flag bit (EIF2:IF20) is set to 1 and external interrupt
circuit 2 generates and issues an interrupt request (IRQA) to the CPU. Write 0 for the IF20 bit
within the interrupt processing routine, thus clearing the interrupt request.
When the external interrupt request flag bit (IF20) is set to 1, external interrupt circuit 2
generates the interrupt request, even if external interrupt inputs to the pin are set to disabled by
the bit corresponding to the pin among the interrupt enable bits (IE20 to IE27) of the external
interrupt 2 control register (EIE2), until the IF20 bit is cleared.
Therefore, the IF20 bit must
always be cleared.
If the "L" level input to the external interrupt pin continues as is, even if the IF20 bit is cleared
with external interrupt inputs to the pin remaining enabled, the IF20 bit is immediately set to 1
again. Disable external interrupt inputs to the pin or remove the cause of the external interrupt
as required.
Caution:
When enabling interrupts to the CPU following a release from the reset state, clear the IF20
bit in advance.
Tip:
"L" level inputs to external interrupt pins (INT20 to INT27) trigger external interrupt circuit 2 to
generate the same interrupt request (IRQA).
Thus, when an external interrupt input is
detected, it is necessary to identify the pin at which the input occurs by reading the port 0
data register (PDR0) before the input changes to "H" level.
Only external interrupt circuits 1 and 2 can execute a release from the stop mode by an
interrupt.
s Register Associated with Interrupt Generation by External Interrupt Circuit 2 and Vector Table
For interrupt operation, see Secti
on 3.4.2 "Steps in the Interrupt Operation".
Table 11.5-1 Register Associated with Interrupt Generation by External Interrupt Circuit 2 and Vector
Table
Interrupt designation
Interrupt level setting register
Vector table address
Register
Bit for setting level
Upper
Lower
IRQA
ILR3 (007DH)
LA1 (bit5)
LA0 (bit4)
FFE6H
FFE7H