ProSoft Technology ProLinx S3964R User Manual download pdf (Page 98)

98 Publication LOGIX-AP010B-EN-P - May 2010

Chapter 4 Additional RSLogix 5000 Features

Asynchronous I/O Updating

In Logix systems, I/O is updated asynchronously with respect to program

execution periods. In contrast, S5 uses the traditional PLC approach where an

I/O image table is updated at the start of the cycle and input values do not

change during an execution of the program.

When converting from S5 to Logix, consider if you must buffer input data so

its value remains constant during a program-scan cycle. To keep the value

constant, copy the inputs to memory variables at the start of the program and

then use these memory variables, instead of the inputs, throughout the code.

DINT Data Type

Logix controllers operate on DINT (32 bit integer) tags more efficiently than

on INT (16 bit integer) or SINT (8 bit integer). Use DINT whenever possible,

even if the range of values would fit in an INT or a SINT. These data types are

provided for IEC61131-3 compatibility reasons, but are internally converted to

DINTs before being used by the program. Therefore, code will execute more

efficiently in most situations.

String Data Type

The S5 permits ASCII characters to be stored in datablock locations but there

are no instructions available in S5 to manipulate text strings. In RSLogix 5000

software, it is possible to define a variable of type STRING and to manipulate

these string variables with the following instructions:

• Find –finds the starting position of a string within another string.

• Insert –inserts ASCII characters at a specified location in a string.

• Concat –adds ASCII characters to the end of a string.

• Mid –copies a specified number of characters from a string and stores

them in another string.

• Delete –removes ASCII characters from a string.

• File Search and Compare (FSC) – finds a string in an array of strings

In RSLogix 5000 software, the following comparison operations can be

performed on string variables and numerical variables. The hexadecimal value

of each character is used to determine the value of a string where the

hexadecimal values are determined from the ASCII character code table.

• Compare (CMP)

• Equal (EQU)

• Not Equal (NEQ)

• Greater Than Or Equal GEQ)

• Greater Than (GRT)

• Less Than or Equal (LEQ)

• Less Than (LES)

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ProSoft Technology ProLinx S3964R User Manual Page 98