CHAPTER 10 INTERRUPT FUNCTIONS
User’s Manual U18172EJ2V0UD
175
Figure 10-9. Example of Multiple Interrupts (1/2)
Example 1. Multiple interrupts are acknowledged
INTyy
EI
Main processing
EI
INTyy servicing
INTxx servicing
RETI
IE = 0
INTxx
RETI
IE = 0
During interrupt INTxx servicing, interrupt request INTyy is acknowledged, and multiple interrupts are generated.
Before each interrupt request acknowledgement, the EI instruction is issued, the interrupt mask is released, and the
interrupt request acknowledgement enable state is set.
Caution Multiple interrupts can be acknowledged even for low-priority interrupts.
Example 2. Multiple interrupts are not generated because interrupts are not enabled
INTyy
EI
Main processing
RETI
INTyy servicing
INTxx servicing
IE = 0
INTxx
RETI
INTyy is held pending
IE = 0
Because interrupts are not enabled in interrupt INTxx servicing (the EI instruction is not issued), interrupt request
INTyy is not acknowledged, and multiple interrupts are not generated. The INTyy request is held pending and
acknowledged after the INTxx servicing is performed.
IE = 0: Interrupt request acknowledgment disabled