uPD789074 Subseries 8-Bit Single-Chip Microcontrollers UD - Home

CHAPTER 10 INTERRUPT FUNCTIONS10.4 Interrupt Processing Operation10.4.1 Non-maskable interrupt request acknowledgment operationThe non-maskable interrupt request is unconditionally acknowledged even when interrupts are disabled. It is notsubject to interrupt priority control and takes precedence over all other interrupts.When the non-maskable interrupt request is acknowledged, the PSW and PC are saved to the stack in that order,the IE flag is reset to 0, the contents of the vector table are loaded to the PC, and then program execution branches.Figure 10-6 shows the flowchart from non-maskable interrupt request generation to acknowledgment. Figure 10-7shows the timing of non-maskable interrupt request acknowledgment. Figure 10-8 shows the acknowledgmentoperation if multiple non-maskable interrupts are generated.Caution During a non-maskable interrupt service program execution, do not input another nonmaskableinterrupt request; if it is input, the service program will be interrupted and the newinterrupt request will be acknowledged.158User’s Manual U14801EJ3V1UD