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Chapter 8
Interrupt/Exception Processing Function
Preliminary User’s Manual U15839EE1V0UM00
8.5.2 Restore
Recovery from software exception processing is carried out by the RETI instruction.
By executing the RETI instruction, the CPU carries out the following processing and shifts control to the
restored PC’s address.
(1)
Loads the restored PC and PSW from EIPC and EIPSW because the EP bit of the PSW is 1.
(2) Transfers control to the address of the restored PC and PSW.
Figure 8-22 illustrates the processing of the RETI instruction.
Figure 8-22:
RETI Instruction Processing
Caution:
When the PSW.EP bit and the PSW.NP bit are changed by the LDSR instruction dur-
ing the software exception processing, in order to restore the PC and PSW correctly
during recovery by the RETI instruction, it is necessary to set PSW.EP back to 1
using the LDSR instruction immediately before the RETI instruction.
Remark:
The solid lines show the CPU processing flow.
PSW.EP
RETI instruction
PC
PSW
EIPC
EIPSW
PSW.NP
Original processing restored
PC
PSW
FEPC
FEPSW
1
1
0
0
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