MITSUBISHI
ELECTRIC
15
MITSUBISHI MICROCOMPUTERS
4250 Group
SINGLE-CHIP 4-BIT CMOS MICROCOMPUTER
Table 4 Interrupt request flag, interrupt enable bit and
skip instruction
Request flag
EXF0
T1F
Timer 1 interrupt
Interrupt name
External interrupt
Enable bit
V1
0
V1
1
Skip instruction
SNZ0
SNZ1
Table 5 Interrupt enable bit function
Occurrence of
interrupt request
Enabled
Disabled
Skip instruction
Invalid
Valid
Interrupt enable bit
1
0
INTERRUPT FUNCTION
The interrupt type is a vectored interrupt branching to an
individual address (interrupt address) according to each in-
terrupt source. An interrupt occurs when the following 3
conditions are satisfied.
An interrupt activated condition is satisfied
(request flag = “1”)
Interrupt enable bit = “1”
(interrupt request occurrence enabled)
Interrupt enable flag (INTE) = “1” (interrupt enabled)
Table 3 shows interrupt sources. (Refer to each interrupt
request flag for details of activated conditions.)
(1) Interrupt enable flag (INTE)
The interrupt enable flag (INTE) controls whether the
every interrupt enable/disable. Interrupts are enabled
when INTE flag is set to “1” with the EI instruction and
disabled when INTE flag is cleared to “0” with the DI
instruction. When any interrupt occurs, the INTE flag is
automatically cleared to “0,” so that other interrupts
are disabled until the EI instruction is executed.
(2) Interrupt enable bit (V1
0
, V1
1
)
Use an interrupt enable bit of interrupt control register
V1 to select the corresponding interrupt or skip instruc-
tion.
Table 4 shows the interrupt request flag, interrupt en-
able bit and skip instruction.
Table 5 shows the interrupt enable bit function.
(3) Interrupt request flag
When the activated condition for each interrupt is sat-
isfied, the corresponding interrupt request flag is set to
“1.” Each interrupt request flag is cleared to “0” when
an interrupt occurs, or
the next instruction is skipped with a skip instruc-
tion.
Each interrupt request flag is set when the activated
condition is satisfied even if the interrupt is disabled
by the INTE flag or its interrupt enable bit. Once set,
the interrupt request flag retains set until a clear con-
dition is satisfied.
Accordingly, an interrupt occurs when the interrupt dis-
able state is released while the interrupt request flag
is set.
If more than one interrupt request flag is set when the
interrupt disable state is released, the interrupt priority
level is as follows shown in Table 3.
Table 3 Interrupt sources
Priority
level
1
External interrupt
2
Interrupt name
Timer 1 interrupt
Interrupt
address
Address 0
in page 1
Address 2
in page 1
Activated condition
Level change of INT
pin
Timer 1 underflow