MITSUBISHI MICROCOMPUTERS
38B5 Group
SINGLE-CHIP 8-BIT CMOS MICROCOMPUTER
16
PRELIMINARY
Notice: This s not a final specification.
Some parametric imits are subject to change.
Interrupts
Interrupts occur by twenty one sources: five external, fifteen internal,
and one software.
(1) Interrupt Control
Each interrupt except the BRK instruction interrupt have both an
interrupt request bit and an interrupt enable bit, and is controlled by
the interrupt disable flag. An interrupt occurs if the corresponding
interrupt request and enable bits are “1” and the interrupt disable flag
is “0.” Interrupt enable bits can be set or cleared by software. Inter-
rupt request bits can be cleared by software, but cannot be set by
software. The BRK instruction interrupt and reset cannot be disabled
with any flag or bit. The I flag disables all interrupts except the BRK
instruction interrupt and reset. If several interrupts requests occurs
at the same time the interrupt with highest priority is accepted first.
(2) Interrupt Operation
Upon acceptance of an interrupt the following operations are auto-
matically performed:
1. The contents of the program counter and processor status
register are automatically pushed onto the stack.
2. The interrupt disable flag is set and the corresponding
interrupt request bit is cleared.
3. The interrupt jump destination address is read from the vector
table into the program counter.
I
Notes on Use
When the active edge of an external interrupt (INT
0
–INT
4
) is set or
when switching interrupt sources in the same vector address, the
corresponding interrupt request bit may also be set. Therefore, please
take following sequence:
(1) Disable the external interrupt which is selected.
(2) Change the active edge in interrupt edge selection register
(3) Clear the set interrupt request bit to “0.”
(4) Enable the external interrupt which is selected.