SINGLE-CHIP 8-BIT CMOS MICROCOMPUTER
Interrupts occur by 16 sources among 21 sources: nine external,
eleven internal, and one software.
Each interrupt is controlled by an interrupt request bit, an interrupt
enable bit, and the interrupt disable flag except for the software in-
terrupt set by the BRK instruction. An interrupt occurs if the
corresponding interrupt request and enable bits are “1” and the in-
terrupt disable flag is “0”.
Interrupt enable bits can be set or cleared by software.
Interrupt request bits can be cleared by software, but cannot be
set by software.
The BRK instruction cannot be disabled with any flag or bit. The I
(interrupt disable) flag disables all interrupts except the BRK in-
When several interrupts occur at the same time, the interrupts are
received according to priority.
By acceptance of an interrupt, the following operations are auto-
1. The contents of the program counter and the 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.
Interrupt Source Selection
Any of the following interrupt sources can be selected by the inter-
rupt source selection register (address 003916).
1. INT0 or Input buffer full
2. INT1 or Output buffer empty
3. Serial I/O1 transmission or SCLSDA
4. CNTR0 or SCLSDA
5. Serial I/O2 or I2C
6. INT2 or I2C
7. CNTR1 or Key-on wake-up
8. A-D conversion or Key-on wake-up
External Interrupt Pin Selection
The occurrence sources of the external interrupt INT2, INT3, and
INT4 can be selected from either input from INT20, INT30, INT40
pin, or input from INT21, INT31, INT41 pin by the INT2, INT3, INT4
interrupt switch bit (bit 4 of address 002F16).
When setting of the following register or bit is changed, the inter-
rupt request bit may be set to “1.”
• Interrupt edge selection register (address 003A16)
• Interrupt source selection register (address 003916)
• INT2, INT3, INT4 interrupt switch bit of Port control register 2 (bit
4 of address 002F16)
Accept the interrupt after clearing the interrupt request bit to “0”
after interrupt is disabled and the above register or bit is set.