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4
EIT
4-8
32185/32186 Group Hardware Manual
Rev.1.10 REJ09B0235-0110 May 15, 07
4.5 Acceptance of EIT Events
When an EIT event occurs, the CPU suspends the program it has hitherto been executed and branches to
EIT processing by the relevant handler. Conditions under which each EIT event occurs and the timing at
which they are accepted are shown below.
Table 4.5.1 Acceptance of EIT Events
EIT Event
Type of Processing
Acceptance Timing
Values Set in BPC Register
Reserved Instruction
Instruction processing-
During instruction execution
PC value of the instruction that
Exception (RIE)
canceled type
generated RIE
Address Exception (AE)
Instruction processing-
During instruction execution
PC value of the instruction that
canceled type
generated AE
Floating-Point Exception
Instruction processing-
Break in instructions
PC value of the instruction that
(FPE)
completed type
generated FPE + 4
Reset Interrupt (RI)
Instruction processing-
Each machine cycle
Undefined value
aborted type
System Break Interrupt
Instruction processing-
Break in instructions
PC value of the next instruction
(SBI)
completed type
(word boundary only)
External Interrupt (EI)
Instruction processing-
Break in instructions
PC value of the next instruction
completed type
(word boundary only)
Trap (TRAP)
Instruction processing-
Break in instructions
PC value of TRAP instruction + 4
completed type
4.6 Saving and Restoring PC and PSW
The following describes operation of the microcomputer at the time when it accepts an EIT and when it
executes the RTE instruction.
(1) Hardware preprocessing when an EIT is accepted
[1] Save the PSW register’s SM, IE and C bits in its backup field.
BSM
←
SM
BIE
←
IE
BC
←
C
[2] Update the PSW register’s SM, IE and C bits
SM
←
Remains unchanged (RIE, AE, FPE, TRAP) or cleared to "0" (SBI, EI, RI)
IE
←
Cleared to "0"
C
←
Cleared to "0"
[3] Save the PC register
BPC
←
PC
[4] Set the vector address in the PC register
Branches to the EIT vector and executes the branch (BRA) instruction written in it, thereby transfer-
ring control to the user-created EIT handler.
(2) Hardware postprocessing when the RTE instruction is executed
[A] Restore the PSW register’s SM, IE and C bits from its backup field.
SM
←
BSM
IE
←
BIE
C
←
BC
[B] Restore the PC register from the BPC register.
PC
←
BPC
Note: The values stored in the BPC and the PSW register’s BSM, BIE and BC bits after executing the RTE
instruction are undefined.
4.5 Acceptance of EIT Events