
1.OVERVIEW OF PMC B-63983EN/02
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1.2.4 Graphic Symbols of Relays and Coils
Ladder diagrams use the following relay symbols:
Relays (contacts)
Instruction
representation
Function
-| |-
Normally open contact
(contact A)
-|/ |-
Normally closed contact
(contact B)
Coils
Instruction
representation
Function
-¡-Coil
-¡¡- Negated coil
-(S)- Set coil
-(R)- Reset coil
These instructions perform a 1-bit operation and are called basic
instructions.
In addition, there are functional instructions that enable easy
programming of complicated operations for processing byte, word, and
double-word data, which are difficult to program just using basic
instructions. The symbol formats of the functional instructions are
slightly different from instruction to instruction. For details, see the
description of each functional instruction in Chapter 4.
1.2.5 Line Number and Net Number
A line number is indicated in every line of ladder diagrams.
A continuous ladder circuit from a contact to a coil is called a net. A
net number is also indicated for each net.