38C3 datasheet(16/63 Pages) RENESAS

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SINGLE-CHIP 8-BIT CMOS MICROCOMPUTER

MITSUBISHI MICROCOMPUTERS

38C3 Group

INTERRUPTS

Interrupts occur by sixteen sources: six external, nine internal, and

one software.

Interrupt Control

Each interrupt except the BRK instruction interrupt have both an in-

terrupt request bit and an interrupt enable bit, and is controlled by the

interrupt disable flag. An interrupt occurs if the corresponding inter-

rupt request and enable bits are “1” and the interrupt disable flag is

“0”.

Interrupt enable bits can be set or cleared by software. Interrupt re-

quest 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.

Interrupt Operation

By acceptance of an interrupt, the following operations are automati-

cally performed:

1. The processing being executed is stopped.

2. The contents of the program counter and processor status reg-

ister are automatically pushed onto the stack.

3. The interrupt disable flag is set and the corresponding interrupt

request bit is cleared.

4. The interrupt jump destination address is read from the vector

table into the program counter.

sNotes on Interrupts

When the active edge of an external interrupt (INT0 – INT2, CNTR0

or CNTR1) is set or an vector interrupt source where several interrupt

source is assigned to the same vector address is switched, the cor-

responding interrupt request bit may also be set. Therefore, take fol-

lowing sequence:

(1) Disable the interrupt.

(2) Change the active edge in interrupt edge selection register.

(3) Clear the set interrupt request bit to “0.”

(4) Enable the interrupt.

38C3 Datasheet(PDF) 16 Page - Renesas Technology Corp