Preface
MicroLogix 1000 Programmable Controllers User Manual
4–14
When
entering values into an instruction or data table element, you can specify the
radix of your entry using the “&” special operator
. The radixes that can be used to
enter data into an instruction or data table element are:
• Integer (&N)
• Binary (&B)
• ASCII (&A)
• Hexadecimal (&H)
• BCD (&D)
• Octal (&O)
Numeric constants are used in place of data file elements. They cannot be
manipulated by the user program. You must enter the offline program editor to
change the value of a constant.
Applying Ladder Logics to Your Schematics
The logic you enter into the micro controller makes up a ladder program. A ladder
program consists of a set of instructions used to control a machine or a process.
Ladder logic is a graphical programming language based on electrical relay
diagrams. Instead of having electrical rung continuity, ladder logic is looking for
logical rung continuity. A ladder diagram identifies each of the elements in an
electromechanical circuit and represents them graphically
. This allows you to see
how your control circuit operates before you actually start the physical operation of
your system.
1
]/[
I
] [
( )
O
1
I
input instructions output instruction
0
In a ladder diagram each of the input devices are represented in series or parallel
combinations across the rung of the ladder. The last element on the rung is the
output that receives the action as a result of the conditional state of the inputs on the
rung.
Each output instruction is executed by the controller when the rung is scanned and
the conditions on the rung are true. When the rung is not scanned or the logic
conditions on the rung do not create a true logic path, the output is not executed.
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