Basic Ladder Diagrams; Basic Terms - Omron SYSMAC CV Series Operation Manual

Basic Ladder Diagrams

4-3

Basic Ladder Diagrams

4-3-1 Basic Terms

Normally Open and
Normally Closed
Conditions
0000
00
Normally open
0000
00
condition
Normally closed
condition
A ladder diagram consists of two vertical lines running down the sides with lines
branching in between them. The vertical lines are called bus bars; the branch-
ing lines, instruction lines or rungs. Along the instruction lines are placed
conditions that lead to other instructions next to the right bus bar. The logical
combinations of the conditions on the instruction lines determine when and how
the instructions at the right are executed. A ladder diagram is shown below.
0000 0063 0252 0001 0025
00 15 08 09 03
0000 0005
01 01
0001 0000 0000 0000 0000
00 02 03 50 07
0000
10
0000
11
As shown in the diagram above, instruction lines can branch apart and they can
join back together. The short 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 diago-
nal 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. Only these conditions and a limited number of intermediate
instructions can appear along the instruction lines. All other instructions must
appear next to the right bus bar. Instructions that appear next to the right bus bar
are called right-hand instructions.
The way the operation of each of the instructions corresponds to a condition is
described below. Before we consider these, however, there are some basic
terms that must be explained.
Each condition in a ladder diagram is either ON or OFF depending on the status
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 something to happen when a
bit is ON, and a normally closed condition when you want something to happen
when a bit is OFF.
0244 0244
00 01
0005 0005 0005
02 03 04
T000 0005 0004 0004
01 15 03 05
0210 0210
01 02
0210 0210
05 07
Instruction is executed when
Instruction
CIO bit 00000 is ON.
Instruction is executed when
Instruction
CIO bit 00000 is OFF.
Section 4-3
Instruction
Instruction
75