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395
User’s Manual U14260EJ3V1UD
CHAPTER 19 INTERRUPT FUNCTIONS
19.1 Interrupt Function Types
The following three types of interrupt functions are used.
(1) Non-maskable interrupts
A non-maskable interrupt is acknowledged even when interrupts are disabled. It does not undergo priority control
and is given top priority over all other interrupt requests. However, interrupt requests are held pending during
non-maskable interrupt servicing.
A non-maskable interrupt generates a standby release signal and releases the HALT mode during main system
clock operation.
The only non-maskable interrupt in the
μ
PD780078 Subseries is the interrupt from the watchdog timer.
(2) Maskable interrupts
These interrupts undergo mask control. Maskable interrupts can be divided into a high interrupt priority group
and a low interrupt priority group by setting the priority specification flag registers (PR0L, PR0H, PR1L).
High priority interrupts can be serviced preferentially to low priority interrupts (multiple interrupt servicing). If two
or more interrupts with the same priority are generated simultaneously, each interrupt has a predetermined priority
(see
Table 19-1
).
A standby release signal is generated and the STOP mode and HALT mode are released.
Five external interrupt requests and 18 internal interrupt requests (19 internal interrupt requests for the
μ
PD780078Y Subseries) are incorporated as maskable interrupts.
(3) Software interrupts
A software interrupt is a vectored interrupt that is generated by executing the BRK instruction. It is acknowledged
even when interrupts are disabled. A software interrupt does not undergo interrupt priority control.
19.2 Interrupt Sources and Configuration
A total of 25 interrupt sources (26 interrupt sources for the
μ
PD780078Y Subseries) exist among non-maskable,
maskable, and software interrupts (see
Table 19-1
).
Remark
A non-maskable interrupt or maskable interrupt (internal) can be selected as the watchdog timer interrupt
source (INTWDT).