ALLEN BRADLEY LADDER LOGIC PROGRAM HOW TO
ALLEN BRADLEY LADDER LOGIC PROGRAM CODE

For instance, if a string has space for 80 characters, but is filled with the characters вЂњToday is Tuesday, September 13вЂќ then LEN = 30.вЂќД¬oncatenate (CONCAT) вЂ“ Connect two strings together, one after another. Strings may also contain a length (LEN) field that contains the number of characters that exist in the string. These can be found in a standard ASCII table there is one in the appendix of this manual. These equate to the decimal numbers 84, 101, 120, 116 or the hex numbers 54, 65, 78, 74. If in text, they are often displayed with a вЂњ$вЂќ sign before the character, such as Text = $T, $e, $x, $t characters. Values contained in strings can be displayed as decimal or hexadecimal numbers, or as text characters. The array elements contain ASCII characters, which can be thought of as printable characters with a few non-printable commands included. вЂњAs mentioned in the data section of this manual, strings are arrays of SINTs, or Single Integers (Bytes). This is reprinted from my recently published training manual, вЂњPLC Hardware and Programming, Multi-PlatformвЂќ: While this is a good exercise in explaining how data may be encoded, bar codes actually read ASCII strings that have to be decoded in a different way.ДЇollowing are some of the common string manipulation instructions used in PLCs, along with their purpose. The lesson usually uses masks, rotates and bit shifts to extract sections of the DINT representing a product color, type or other value. In some PLC classes there are lessons where students are given a Double Integer (DINT) that is supposed to represent a bar code. The Null, SOH, STX and ETX characters are often used in interfacing with devices such as printers. As a matter of fact, there are 95 printable characters in Standard ASCII, while the other characters are made up of other keyboard-related commands such as backspace, tab and carriage return/line feed. The standard ASCII table has 128 (0-127) characters, while there are also 8 bit (or more) variants that include characters such as pi, foreign currency symbols and others.ДЄs you can see in the above picture, not all ASCII characters are printable. Notice that there are only 7 bits in the Binary column the original teleprinter based encoding left open the option of using the eighth bit for parity checking when the bits were transmitted serially.

The tables above show some of the printable characters and their corresponding values in Binary, Octal, Decimal and Hexadecimal.

While it isnвЂ™t the only method of turning printable characters into numbers that PLCs can deal with, it is the one most commonly used in the US.

ALLEN BRADLEY LADDER LOGIC PROGRAM CODE

The program communicated with a PC-based Cognex machine vision system that sent and received strings of data for everything from its camera triggering to its reporting of positional data for the object it was inspecting.ДЇirst lets talk about ASCII: American Standard Code for Information Interchange is a byte-based encoding of text into numerical values. The picture above is from a ControlLogix program (Allen-Bradley, RSLogix5000 v.16) I wrote back in 2006.

ALLEN BRADLEY LADDER LOGIC PROGRAM HOW TO

TodayвЂ™s post covers ASCII, string manipulation and how to deal with readable text in a PLC.

Allen bradley ladder logic program