Understanding The Programming Languages; Understanding The Basic Elements Of Ladder - Siemens Simatic S7-200 CPU 210 System Manual

4.4

Understanding the Programming Languages

The CPU 210 and STEP 7-Micro/WIN support the following programming languages:
Statement list (STL) is a set of mnemonic instructions that represent functions of the
CPU.
Ladder is a graphical language that resembles the electrical relay diagrams for the
equipment.
STEP 7-Micro/WIN also provides two representations for displaying the addresses and the
programming instructions in the program: International and SIMATIC. Both the international
and SIMATIC representations refer to the same CPU 210 instruction set. There is a direct
correspondence between the International and the SIMATIC representation; both
representations have the same functionality.

Understanding the Basic Elements of Ladder

When you write a program in ladder, you create and arrange the graphical components to
form a network of logic. As shown in Figure 4-7, the following types of elements are available
for creating your program:
Contacts: each of these elements represents a switch through which power can flow
when a switch is closed.
Coils: each of these elements represents a relay that is energized by power flowing to
that relay.
Boxes: each of these elements represents a function that is executed when power flows
to the box.
Networks: this element forms a complete circuit. Power flows from the left power rail
through the closed contacts to energize the coils or boxes.
Output Coils
Network 1
I0.0
Normally Open
Contact
Network 2
I0.0
Left Power Rail
Figure 4-7 Basic Elements of Ladder
S7-200 Programmable Controller, CPU 210
C79000-G7076-C235-01
Basic Concepts for Programming the CPU 210
Output
F2
NETWORK TITLE (single line)
I0.1 Q0.0
Normally Closed
Contact
NETWORK TITLE (single line)
T0
TON
IN
Box
PT
+0
F3
F4 F5 F6 F7
Coil
Network
Network
F8 F10
4-9