CHAPTER 7 INTERRUPT/EXCEPTION PROCESSING FUNCTION
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User’s Manual U15195EJ5V0UD
7.3.2 Restore
Recovery from maskable interrupt servicing 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 7-5 illustrates the processing of the RETI instruction.
Figure 7-5. RETI Instruction Processing
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
Note
For details of the ISPR register, see
7.3.6 In-service priority register (ISPR)
.
Caution When the PSW.EP bit and the PSW.NP bit are changed by the LDSR instruction during
maskable interrupt servicing, in order to restore the PC and PSW correctly during 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 instruction.
Remark
The solid lines show the CPU processing flow.