Omron C200H - Basic Ladder Diagrams; Basic Terms

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designated as an operand is called an operand word. If the actual value is
entered as a constant, it is preceded by # to indicate that it is not an address.
Other terms used in describing instructions are introduced in Section 5 In-
struction Set.
4-3 Basic Ladder Diagrams
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
branching lines, 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
Instruction
Instruction
00403
00001
HR 0109 LR 250325208 24400
00501 00502 00503 00504
24401
00100 00002
00010
00011
00003 HR 0050 00007 TIM 001 LR 0515
21001 21002
00405
21005 21007
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. Con-
ditions without diagonal lines through them are called normally open condi-
tions and correspond to a LOAD, AND, or OR instruction. The conditions with
diagonal lines through them are called normally closed conditions and corre-
spond 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 following instructions. The way the operation of each of the in-
structions corresponds 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 a GPC, a FIT, or LSS, a second bus
bar will be shown on the right side of the ladder diagram and will be con-
nected to all instructions on the right side. This does not change the lad-
der-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 in-
structions on the right must be connected directly to the right bus bar. Refer
to the GPC, FIT, or LSS Operation Manual for details.
4-3-1 Basic Terms
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 condi-
tion 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
Normally Open and
Normally Closed
Conditions
Basic Ladder Diagrams Section 4-3