Basic Ladder Diagrams; Basic Terms - Omron CQM1H - PROGRAM Programming Manual

Basic Ladder Diagrams

4-3

Basic Ladder Diagrams

4-3-1

Basic Terms

Normally Open and
Normally closed
Conditions
Other terms used in describing instructions are introduced in SECTION 5
Instruction Set.
A ladder diagram consists of one line running down the left side with lines
branching off to the right. The line on the left is called the bus bar. The branch-
ing lines are called instruction lines or rungs. Along the instruction lines are
placed conditions that lead to other instructions on the right side. The logical
combinations of these conditions determine when and how the instructions at
the right are executed. A ladder diagram is shown below.
00000 06315
• •
00001
•
00100 00002 00003 HR 0050
• •
00010
• •
00011
•
As shown in the diagram above, instruction lines can branch apart and they
can join back together. The vertical pairs of lines are called conditions. Condi-
tions without diagonal lines through them are called normally open conditions
and correspond to a LOAD, AND, or OR instruction. The conditions with diag-
onal lines through them are called normally closed conditions and correspond
to a LOAD NOT, AND NOT, or OR NOT instruction. The number above each
condition indicates the operand bit for the instruction. It is the status of the bit
associated with each condition that determines the execution condition for fol-
lowing instructions. The way the operation of each of the instructions corre-
sponds to a condition is described below. Before we consider these, however,
there are some basic terms that must be explained.
Note When displaying ladder diagrams with the CX-Programmer, a second bus bar
will be shown on the right side of the ladder diagram and will be connected to
all instructions on the right side. This does not change the ladder-diagram
program in any functional sense. No conditions can be placed between the
instructions on the right side and the right bus bar, i.e., all instructions on the
right must be connected directly to the right bus bar. Refer to the CX-Pro-
grammer User Manual for details.
Each condition in a ladder diagram is either ON or OFF depending on the sta-
tus of the operand bit that has been assigned to it. A normally open condition
is ON if the operand bit is ON; OFF if the operand bit is OFF. A normally
closed condition is ON if the operand bit is OFF; OFF if the operand bit is ON.
Generally speaking, you use a normally open condition when you want some-
thing to happen when a bit is ON, and a normally closed condition when you
want something to happen when a bit is OFF.
25208 HR 0109 LR 2503 24400
•
00501 00502
00007 TIM 001 LR 0515
•
21001 21002
•
21005 21007
Section 4-3
24401
• •
00503 00504
•
00403 00405
•
•
Instruction
Instruction
181