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Chapter 8
Interrupt/Exception Processing Function
Preliminary User’s Manual U15839EE1V0UM00
8.3.2 Restore
Recovery from maskable interrupt processing is carried out by the RETI instruction.
When the RETI instruction is executed, the CPU performs the following steps, and transfers control to
the address of the restored PC.
(1) Restores the values of the PC and the PSW from EIPC and EIPSW because the EP bit of the
PSW is 0 and the NP bit of the PSW is 0.
(2) Transfers control to the address of the restored PC and PSW.
Figure 8-7 illustrates the processing of the RETI instruction.
Figure 8-7:
RETI Instruction Processing
Note: For the ISPR register, see 8.3.6 “In-service priority register (ISPR)” on page 220.
Caution:
When the PSW.EP bit and the PSW.NP bit are changed by the LDSR instruction dur-
ing maskable interrupt processing, in order to restore the PC and PSW correctly dur-
ing recovery by the RETI instruction, it is necessary to set PSW.EP back to 0 and
PSW.NP back to 0 using the LDSR instruction immediately before the RETI instruc-
tion.
Remark:
The solid lines show the CPU processing flow.
PSW.EP
RETI instruction
PSW.NP
Restores original processing
1
1
0
0
PC
PSW
Corresponding
bit of ISPR
Note
EIPC
EIPSW
0
PC
PSW
FEPC
FEPSW
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