207
Chapter 8
Interrupt/Exception Processing Function
Preliminary User’s Manual U15839EE1V0UM00
8.2.2 Restore
(1)
NMI0
Execution is restored from the non-maskable interrupt (NMI0) processing 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 8-3 illustrates how the RETI instruction is processed.
Figure 8-3:
RETI Instruction Processing
Caution:
When the PSW.EP bit and PSW.NP bit are changed by the LDSR instruction during
non-maskable interrupt 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 0 and
PSW.NP back to 1 using the LDSR instruction immediately before the RETI instruc-
tion.
Remark:
The solid line indicates the CPU processing flow.
(2)
NMIWDT
Restoring by RETI instruction is not possible. Perform a system reset after interrupt servicing.
PSW.EP
RETI instruction
PSW.NP
Original processing restored
1
1
0
0
PC
PSW
EIPC
EIPSW
PC
PSW
FEPC
FEPSW
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