4500/720 Series 720 Family Models 4513, 4514 Group User's Manual

4513/4514 Group User’s Manual
HARDWARE
1-23
FUNCTION BLOCK OPERATIONS
(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)
Fig. 13 Program example of interrupt processing
• 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
The address of main routine to be
executed when returning
Fig. 15 Interrupt system diagram
Fig. 14 Internal state when interrupt occurs
T1F V12
EXF1 V11
EXF0
V10
Address 2
in page 1
Address 4
in page 1
Address 0
in page 1
T4F V21
T3F V20
T2F V13
Address 8
in page 1
Address A
in page 1
Address 6
in page 1
SIOF V23
ADF V22
Completion of
serial I/O transfer
Timer 1
underflow
Timer 4
underflow
Timer 3
underflow
Timer 2
underflow
Completion of
A-D conversion
Address E
in page 1
Address C
in page 1
Request flag
(state retained)
Enable
bit
Enable
flag
INTE
Activated
condition
INT0 pin
(L→H or
H→L input)
INT1 pin
(L→H or
H→L input)
EI
RTI
Interrupt
service routine
Interrupt
occurs
Interrupt is
enabled
Main
routine
: Interrupt enabled state
: Interrupt disabled state
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