
66
Chapter 3
CPU Function
User’s Manual U16702EE3V2UD00
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NMI status saving registers (FEPC and FEPSW)
FEPC and FEPSW are used to save the status when a non-maskable interrupt (NMI) occurs.
If an NMI occurs, the contents of the program counter (PC) are saved to FEPC, and those of the
program status word (PSW) are saved to FEPSW.
The address of the instruction next to the one of the instruction under execution, except some
instructions, is saved to FEPC when an NMI occurs.
The current contents of the PSW are saved to FEPSW.
Because only one set of NMI status saving registers is available, the contents of these registers
must be saved by program when multiple interrupts are enabled.
Bits 31 to 26 of FEPC and bits 31 to 8 of FEPSW are reserved for future function expansion (these
bits are always fixed to 0).
Figure 3-4:
NMI Status Saving Registers (FEPC and FEPSW) Format
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Interrupt source register (ECR)
The interrupt source register (ECR) holds the source of an exception or interrupt if an exception or
interrupt occurs. This register holds the exception code of each interrupt source. Because this reg-
ister is a read-only register, data cannot be written to this register using the LDSR instruction.
Figure 3-5:
Interrupt Source Register (ECR) Format
The list of exception codes is tabulated in
Table 17-1, “Interrupt/Exception Source List,” on
page 685
.
Bit position
Bit name
Meaning
31 to 16
FECC
Exception code of non-maskable interrupt (NMI)
15 to 0
EICC
Exception code of exception or maskable interrupt
31
0
FEPC
(PC contents)
0
0
After reset
0xxxxxxxH
(x: Undefined)
26 25
0 0 0 0
31
0
FEPSW
(PSW contents)
0
0
After reset
000000xxH
(x: Undefined)
8
0 0 0 0
0
0
0 0 0 0
0
0
0 0 0 0
0
0
0 0 0 0
31
0
ECR
FECC
EICC
After reset
00000000H
16 15
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