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(4) Internal state during an interrupt
The internal state of the microcomputer during an interrupt is as
follows (Figure 14).
• Program counter (PC)
An interrupt address is set in program counter. The address to be
executed when returning to the main routine is automatically
stored in the stack register (SK).
• Interrupt enable flag (INTE)
INTE flag is cleared to "0" so that interrupts are disabled.
• Interrupt request flag
Only the request flag for the current interrupt source is cleared to
"0."
• Data pointer, carry flag, skip flag, registers A and B
The contents of these registers and flags are stored automati-
cally in the interrupt stack register (SDP).
(5) Interrupt processing
When an interrupt occurs, a program at an interrupt address is ex-
ecuted after branching a data store sequence to stack register.
Write the branch instruction to an interrupt service routine at an in-
terrupt address.
Use the RTI instruction to return from an interrupt service routine.
Interrupt enabled by executing the EI instruction is performed after
executing 1 instruction (just after the next instruction is executed).
Accordingly, when the EI instruction is executed just before the RTI
instruction, interrupts are enabled after returning the main routine.
(Refer to Figure 13)
Main
routine
Interrupt
occurs
Interrupt is
enabled
Fig. 13 Program example of interrupt processing
Interrupt
service routine
•
•
•
•
EI
RTI
: Interrupt enabled state
: Interrupt disabled state
4513/4514 Group User's Manual
FUNCTION BLOCK OPERATIONS
• Program counter (PC)
.............................................................. Each interrupt address
• Stack register (SK)
....................................................................................................
• Interrupt enable flag (INTE)
.................................................................. 0 (Interrupt disabled)
• Interrupt request flag (only the flag for the current interrupt
source) ................................................................................... 0
• Data pointer, carry flag, registers A and B, skip flag
........ Stored in the interrupt stack register (SDP) automatically
Fig. 14 Internal state when interrupt occurs
INT0 pin
(L H or
EXF0
H L input)
INT1 pin
(L H or
EXF1
H L input)
Timer 1
underflow
T1F
Timer 2
underflow
T2F
Timer 3
underflow
T3F
Timer 4
underflow
T4F
Completion of
A-D conversion
ADF
Completion of
serial I/O transfer
SIOF
Activated
Request flag
condition
(state retained)
Fig. 15 Interrupt system diagram
HARDWARE
The address of main routine to be
executed when returning
Address 0
in page 1
V1
0
Address 2
in page 1
V1
1
Address 4
in page 1
V1
2
Address 6
in page 1
V1
3
Address 8
in page 1
V2
0
Address A
in page 1
V2
1
Address C
in page 1
V2
2
Address E
in page 1
INTE
V2
3
Enable
Enable
bit
flag
1-23
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