Mitsubishi Digital Electronics FX2NC Manual

A SERVICE OF

next previous

FX Series Programmable Controllers Execution Times And Instructional Hierarchy 7

7-14

7.4 Batch Processing

This is the s

y

stem used b

y

all members of the FX famil

y

of PLC’s. The basic concept is that

there are three sta

g

es to an

y

pro

g

ram scan. In other words, ever

y

time the pro

g

ram is

processed form start to end the followin

g

sequence of events occurs:

Input processing:

All of the current input statuses are read in to a

temporar

y

memor

y

area; sometimes called an

ima

g

e memor

y

. The PLC is now read

y

for the next

pro

g

ram processin

g

.......

Program processing:

All of the updated inputs are checked as the

pro

g

ram is processed. If the new input statuses

chan

g

e the status of driven outputs, then these are

noted in the ima

g

e memor

y

for the......

Output processing:

The new, current statuses of the outputs which

have

j

ust be processed are ph

y

sicall

y

updated, i.e

rela

y

s are turned ON or OFF as required. The

pro

g

ram scan starts a

g

ain............

The s

y

stem is known as 'Batch processin

g

'

because all of the inputs, pro

g

ram operation and finall

y

the outputs are processed as batches.

7.5 Summary of Device Memory Allocations

The memor

y

allocations of the pro

g

rammable are ver

y

complex, but from a users point of view

there are three main areas:

a) The Pro

g

ram Memor

y

:

This memor

y

area holds all of the data re

g

ardin

g

: parameters, sequence pro

g

ram, constant

values K and H, pointer information for P and I devices, nest level information, file re

g

ister

contents/allocations and also the pro

g

ram comment area.

- This memor

y

area is latched either b

y

batter

y

backup or b

y

use of EEPROM pro

g

ram

mana

g

ement (dependent on the PLC bein

g

used). An

y

data stored in this area is kept

even when the PLC is powered down. The duration and reliabilit

y

of the data stora

g

e is

dependent upon the condition of the batter

y

or EEPROM bein

g

used to perform the

backup process.

Input Processing

Program Processing

Output Processing