Software Interrupt Request Acknowledge Operation - NEC mPD780852 Series Preliminary User's Manual

Figure 19-12. Interrupt Request Acknowledge Timing (Minimum Time)
CPU processing
××IF
(××PR = 1)
××IF
(××PR = 0)
Remark 1 clock: 1/f
CPU
Figure 19-13. Interrupt Request Acknowledge Timing (Maximum Time)
CPU processing
××IF
(××PR = 1)
××IF
(××PR = 0)
Remark 1 clock: 1/f
CPU

19.4.3 Software interrupt request acknowledge 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 are saved into the stacks in the order of the program
status word (PSW), then program counter (PC), the IE flag is reset (to 0), and the contents of the vector table (003EH,
003FH) are loaded into PC and branched.
Return from a software interrupt is possible with the RETB instruction.
Caution Do not use the RETI instruction for returning from the software interrupt.
CHAPTER 19 INTERRUPT FUNCTIONS
Instruction
(f : CPU clock)
CPU
Instruction
(f : CPU clock)
CPU
Preliminary User's Manual U14581EJ3V0UM00
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
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