Software Interrupt Request Acknowledgement - NEC mPD78F0730 Preliminary User's Manual

CPU processing
××IF
(××PR = 1)
××IF
(××PR = 0)
Remark 1 clock: 1/f
CPU processing
××IF
(××PR = 1)
××IF
(××PR = 0)
Remark 1 clock: 1/f

13.4.2 Software interrupt request acknowledgement

A software interrupt acknowledge 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 (003EH,
003FH) are loaded into the PC and branched.
Restoring from a software interrupt is possible by using the RETB instruction.
Caution Do not use the RETI instruction for restoring from the software interrupt.
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CHAPTER 13 INTERRUPT FUNCTIONS
Figure 13-8. Interrupt Request Acknowledgement Timing (Minimum Time)
Instruction
(f : CPU clock)
CPU CPU
Figure 13-9. Interrupt Request Acknowledgement Timing (Maximum Time)
Instruction
(f : CPU clock)
CPU CPU
Preliminary User's Manual U19014EJ1V0UD
6 clocks
PSW and PC saved,
Instruction jump to interrupt
servicing
8 clocks
7 clocks
25 clocks 6 clocks
PSW and PC saved,
Divide instruction jump to interrupt
servicing
33 clocks
32 clocks
Interrupt servicing
program
Interrupt servicing
program