
4.LADDER LANGUAGE B-63983EN/02
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4.1 BASIC INSTRUCTIONS
Designing a sequence program entails drawing a ladder diagram.
Draw a ladder diagram by using relay contact symbols as well as
symbols representing the functional instructions described later. The
logic laid out in the ladder diagram is input to the programmer as a
sequence program.
You can input a sequence program to the programmer in two ways -
the relay symbol input method whereby relay contact symbols and
functional instruction symbols drawn in the ladder diagram are used as
they are (−−, −/−, −¡−, etc.) and the mnemonic format input
method that uses the mnemonic language (PMC instructions such as
RD, AND, and OR).
The relay symbol input method allows the ladder diagram format to be
used as it is, thus letting you input a sequence program in an intuitive,
easy-to-understand manner. You will virtually have no trouble
creating a program even if you have little or no knowledge of the
PMC instructions (basic instructions such as RD, AND, and OR).
In fact, however, the content of a sequence program that is input using
the relay symbol input method is internally converted to instructions
that are equivalent to the corresponding PMC instructions. Also, you
need to fully understand the functionalities of the functional
instructions that are described later. It is therefore necessary for you
to carefully read the descriptions of the basic and functional
instructions that are given later in this manual.
For information about how to input PMC instructions to the
programmer using relay and other symbols, see Chapter 8.
When reading the descriptions of the PMC instructions, keep the
following in mind.
(1) Signal addresses
An address is assigned to every relay coil and contact - that is,
every signal - drawn in a ladder diagram (see Fig. 4.1 (a)). An
address consists of an address number and a bit number. A zero
at the beginning of an address may be omitted. For detailed
information about addresses, see Section 2.2.
Signal name
Relay name
Bit number
ddress number
R9.0
X8.1
Y20.4
R12.6
B
RO
C
Fig. 4.1 (a) Signal addresses