Rockwell-automation Logix5000 Controllers Structured Text Programming Uživatelský manuál stáhnout pdf (Strana 28)

28 Publication 1756-PM007D-EN-P - November 2012

Chapter 1 Program Structured Text

FOR…DO

Use the FOR…DO loop to do something a specific number of times before

doing anything else.

Operands:

Structured Text

Operand Type Format Description

count SINT

INT

DINT

Tag Tag to store count position as the

FOR…DO executes

initial_ value SINT

INT

DINT

Tag

Expression

Immediate

Must evaluate to a number

Specifies initial value for count

final_ value SINT

INT

DINT

Tag

Expression

Immediate

Specifies final value for count, which

determines when to exit the loop

increment SINT

INT

DINT

Tag

Expression

Immediate

(optional) Amount to increment count

each time through the loop

If you don’t specify an increment, the

count increments by 1.

FOR count:= initial_value TO final_value BY

increment DO

<statement>;

END_FOR;

IMPORTANT

Make sure that you do not iterate within the loop too many times in a single

scan.

• The controller does not execute any other statements in the routine until

it completes the loop.

• If the time that it takes to complete the loop is greater than the

watchdog timer for the task, a major fault occurs.

• Consider using a different construct, such as IF...THEN.

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