Mitsubishi Digital Electronics FX0 Manual

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FX Series Programmable Controlers Applied Instructions 5

5-9

5.1.4 IRET, EI, DI

(FNC 03, 04, 05)

General description of an interrupt routine:

An interrupt routine is a section of pro

g

ram which is, when tri

gg

ered, operated immediatel

y

interruptin

g

the main pro

g

ram flow. Once the interrupt has been processed the main pro

g

ram

flow continues from where it was,

j

ust before the interrupt ori

g

inall

y

occurred.

Operation:

Interrupts are tri

gg

ered b

y

different input conditions, sometimes a direct input such as X0 is

used other times a timed interval e.

g

. 30 msec can be used. The availabilit

y

of different

interrupt t

y

pes and the number operational points for each PLC t

y

pe are detailed on pa

g

e 4-

12, Interrupt Pointers. To pro

g

ram and operate interrupt routines requires up to 3 dedicated

instructions (those detailed in this section) and an interrupt pointer.

Defining an interrupt routine:

An interrupt routine is specified between its own

unique interrupt pointer and the first occurrence of an

IRET instruction.

Interrupt routines are ALWAYS pro

g

rammed after an

FEND instruction.

The IRET instruction ma

y

onl

y

be used within

interrupt routines.

Mnemonic Function

Operands

Program steps

D

IRET

FNC 03

(Interrupt

return)

Forces the

pro

g

ram to return

from the active

interrupt routine

N/A

Automaticall

y

returns to the main pro

g

ram step

which was bein

g

processed at the time of the

interrupt call.

IRET:

1 step

EI

FNC 04

(Enable

interrupts)

Enables interrupt

inputs to be pro-

cessed

N/A

An

y

interrupt input bein

g

activated after an EI

instruction and before FEND or DI instructions

will be processed immediatel

y

unless it has

been specificall

y

disabled.

EI:

1 step

DI

FNC 05

(Disable

interrupts)

Disables the

processin

g

of

interrupt routines

N/A

An

y

interrupt input bein

g

activated after a DI

instruction and before an EI instruction will be

stored until the next sequential EI instruction is

processed.

DI:

1 step

I

(Interrupt

pointer)

Identifies the

be

g

innin

g

of an

interrupt routine

A 3 di

g

it numeric code relatin

g

to the interrupt

t

y

pe and operation.

I

:

1 step

FEND

I001

IRET

IRET

I201

Interrupt Program I001

Interrupt Program I201