CHAPTER 5 INTERRUPT/EXCEPTION PROCESSING FUNCTION
User’s Manual U13850EJ4V0UM
135
5.3.2 Restore
To restore execution from the maskable interrupt servicing, the RETI instruction is used.
Operation of 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 PC and PSW from EIPC and EIPSW because the EP bit of PSW is 0 and the NP bit of
PSW is 0.
(2) Transfers control to the address of the restored PC and PSW.
The processing of the RETI instruction is shown below.
Figure 5-8. RETI Instruction Processing
RETI instruction
Restores original processing
PC
PSW
EIPC
EIPSW
PSW. EP
1
0
1
0
PC
PSW
FEPC
FEPSW
PSW. NP
Caution When the PSW.EP bit and the PSW.NP bit are changed by the LDSR instruction during the
maskable interrupt service, 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 line shows the CPU processing flow.
Содержание MPD703030A
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