Rockwell-automation Logix5000 Controllers Structured Text Programming Bedienungsanleitung PDF herunterladen (Seite 17)

Publication 1756-PM007D-EN-P - November 2012 17

Program Structured Text Chapter 1

For example:

How Strings Are Evaluated

The hexadecimal values of the ASCII characters determine if one string is less

than or greater than another string.

• When the two strings are sorted as in a telephone directory, the order of

the strings determines which one is greater.

• Strings are equal if their characters match.

• Characters are case sensitive. Upper case “A” ($41) is not equal to lower

case “a” ($61).

Use this format Example

For this situation You’d write

value1 operator value2 If temp is a DINT tag and your specification

says: “If temp is less than 100⋅ then…”

IF temp<100 THEN...

stringtag1 operator stringtag2 If bar_code and dest are string tags and your

specification says: “If bar_code equals dest

then…”

IF bar_code=dest THEN...

char1 operator char2

To enter an ASCII character directly into

the expression, enter the decimal value of

the character.

If bar_code is a string tag and your

specification says: “If bar_code.DATA[0] equals

’A’ then…”

IF bar_code.DATA[0]=65 THEN...

bool_tag := bool_expressions If count and length are DINT tags, done is a

BOOL tag, and your specification says ”If count

is greater than or equal to length, you are done

counting.”

done := (count >= length);

ASCII Characters Hex Codes

1ab $31$61$62

1b $31$62

A $41

AB $41$42

B $42

a $61

ab $61$62

AB < B

a > B

1 2 ... 12 13 14 15 16 17 18 19 20 21 22 ... 39 40

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