RL78/G15 CHAPTER 14 INTERRUPT FUNCTIONS
R01UH0959EJ0110 Rev.1.10 Page 617 of 765
Mar 7, 2023
14.4.2 Software interrupt request acknowledgment
A software interrupt request is acknowledged by BRK instruction execution. Software interrupts cannot be disabled.
If a software interrupt request is acknowledged, the contents are saved into the stacks in the order of the program status
word (PSW), then program counter (PC), the IE flag is reset (0), and the contents of the vector table (0007EH, 0007FH)
are loaded into the PC and branched.
Returning from a software interrupt is possible by using the RETB instruction.
Caution The RETI instruction cannot be used for return from the software interrupt.
14.4.3 Multiple interrupt servicing
Multiple interrupt servicing occurs when another interrupt request is acknowledged during execution of an interrupt.
Multiple interrupt servicing does not occur unless the interrupt request acknowledgment enabled state is selected (IE =
1). When an interrupt request is acknowledged, interrupt request acknowledgment becomes disabled (IE = 0). Therefore,
to enable multiple interrupt servicing, it is necessary to set (1) the IE flag with the EI instruction during interrupt servicing
to enable interrupt acknowledgment.
Moreover, even if interrupts are enabled, multiple interrupt servicing may not be enabled, this being subject to interrupt
priority control. Two types of priority control are available: default priority control and programmable priority control.
Programmable priority control is used for multiple interrupt servicing.
In the interrupt enabled state, if an interrupt request with a priority higher than that of the interrupt currently being
serviced is generated, it is acknowledged for multiple interrupt servicing. If an interrupt with a priority equal to or lower
than that of the interrupt currently being serviced is generated during interrupt servicing, it is not acknowledged for
multiple interrupt servicing. However, when setting the IE flag to 1 during the interruption at level 0, other level 0
interruptions can be allowed.
Interrupt requests that are not enabled because interrupts are in the interrupt disabled state or because they have a
lower priority are held pending. When servicing of the current interrupt ends, the pending interrupt request is
acknowledged following execution of at least one main processing instruction execution.
Table 14-5 shows relationship between interrupt requests enabled for multiple interrupt servicing and Figure 14-10
shows multiple interrupt servicing examples.
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