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Chapter 5
Interrupt Controller (INTC)
Preliminary User’s Manual U17566EE1V2UM00
5.5.3
Exception status flag (EP)
The EP flag is bit 6 of PSW, and is a status flag used to indicate that exception
processing is in progress. It is set when an exception occurs.
5.6 Exception Trap
An exception trap is an interrupt that is requested when an illegal execution of
an instruction takes place. For this microcontroller, an illegal opcode exception
(ILGOP: Illegal Opcode Trap) is considered as an exception trap.
5.6.1
Illegal opcode definition
The illegal instruction has an opcode (bits 10 to 5) of 111111B, a sub-opcode
(bits 23 to 26) of 0111B to 1111B, and a sub-opcode (bit 16) of 0B. An
exception trap is generated when an instruction applicable to this illegal
instruction is executed.
Note
×: Arbitrary
(1)
Operation
If an exception trap occurs, the CPU performs the following processing, and
transfers control to the handler routine:
(1) Saves the restored PC to DBPC.
(2) Saves the current PSW to DBPSW.
(3) Sets the NP, EP, and ID bits of the PSW.
(4) Sets the handler address (00000060H) corresponding to the exception
trap to the PC, and transfers control.
Figure 5-12
illustrates the processing of the exception trap.
31
8
7
6
5
4
3
2
1
0
Initial value
PSW
0
0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 NP
EP
ID
SAT
CY
OV
S
Z
00000020H
Bit position
Bit name
Function
6
EP
Shows that exception processing is in progress.
0: Exception processing not in progress.
1: Exception processing in progress.
15
11 10
5
4
0 31
27 26
23 22
16
×
×
×
×
×
1
1
1
1
1
1
×
×
×
×
×
×
×
×
×
×
0
1
1
1
×
×
×
×
×
×
0
to
1
1
1
1
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