Software Interrupt Request Acknowledgment Operation - NEC mPD780208 Subseries User Manual

Figure 16-13. Interrupt Request Acknowledgment Timing (Minimum Time)
CPU processing
××IF
(××PR = 1)
××IF
(×× PR = 0)
Remark 1 clock cycle = 1/f
Figure 16-14. Interrupt Request Acknowledgment Timing (Maximum Time)
CPU processing
××IF
(×× PR = 1)
××IF
(×× PR = 0)
Remark 1 clock cycle = 1/f

16.4.3 Software interrupt request acknowledgment operation

A software interrupt request is acknowledged by BRK instruction execution. Software interrupts cannot be
disabled.
If a software interrupt request is acknowledged, the contents of the program status word (PSW) and program
counter (PC) are saved in the stacks in that order, the IE flag is reset to 0 and the contents of the vector tables (003EH
and 003FH) are loaded into the 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.
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CHAPTER 16 INTERRUPT AND TEST FUNCTIONS
Instruction
(f : CPU clock)
CPU CPU
Instruction
(f : CPU clock)
CPU CPU
User's Manual U11302EJ4V0UM
PSW and PC save,
Instruction
jump to interrupt
servicing
8 clocks
7 clocks
25 clocks
PSW and PC save,
Divide instruction
jump to interrupt
servicing
33 clocks
32 clocks
6 clocks
Interrupt
servicing
program
6 clocks
Interrupt
servicing
program