CHAPTER 7 INTERRUPTION/EXCEPTION PROCESSING FUNCTION
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User’s Manual U14359EJ4V0UM
7.2.2 Restore
Execution is restored from the non-maskable interrupt servicing by the RETI instruction.
When the RETI instruction is executed, the CPU performs the following processing, and transfers control to the
address of the restored PC.
<1> Restores the values of the PC and the PSW from FEPC and FEPSW, respectively, because the EP bit of
the PSW is 0 and the NP bit of the PSW is 1.
<2> Transfers control back to the address of the restored PC and PSW.
Figure 7-3 illustrates how the RETI instruction is processed.
Figure 7-3. RETI Instruction Processing
PSW.EP
RETI instruction
PSW.NP
Original processing restored
1
1
0
0
PC
PSW
EIPC
EIPSW
PC
PSW
FEPC
FEPSW
Caution
When the PSW.EP bit and PSW.NP bit are changed by the LDSR instruction during non-
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 1 using
the LDSR instruction immediately before the RETI instruction.
Remark
The solid line shows the CPU processing flow.
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