518CHAPTER 22 INTERRUPT FUNCTIONSFigure 22-14. Interrupt Request Acknowledge Timing (Minimum Time)Remark 1 clock: (f CPU : CPU clock)Figure 22-15. Interrupt Request Acknowledge Timing (Maximum Time)Remark 1 clock: (f CPU : CPU clock)22.4.3 Software interrupt request acknowledge operationA software interrupt request is acknowledged by BRK instruction execution. Software interrupt cannot bedisabled.If a software interrupt is acknowledged, the contents of program status word (PSW) and program counter (PC)are saved to stacks, in this order. Then the IE flag is reset (to 0), and the contents of the vector tables (003EHand 003FH) are loaded into PC and branched.Return from the software interrupt is possible with the RETB instruction.Caution Do not use the RETI instruction for returning from the software interrupt.f CPU1Instruction Divide Instruction PSW and PC Save,Jump to InterruptServicing6 ClocksInterruptServicingProgram33 Clocks32 ClocksCPU ProcessingxxIF(xxPR = 1)xxIF(xxPR = 0)25 Clocksf CPU1Instruction Instruction PSW and PC Save,Jump to InterruptServicing6 ClocksInterruptServicingProgram8 Clocks7 ClocksCPU ProcessingxxIF(xxPR = 1)xxIF(xxPR = 0)
