Siemens SIMATIC STEP 7 V5.2 Getting Started page 9

1.2 Combining Hardware and Software
Using the STEP 7 software, you can create your S7 program within a project. The
S7 programmable controller consists of a power supply unit, a CPU, and input and
output modules (I/O modules).
The programmable logic controller (PLC) monitors and controls your machine with
the S7 program. The I/O modules are addressed in the S7 program via the
addresses.
Programming
device cable
Power supply module
STEP 7 Getting Started
A5E00171228-01
Programming device
Transferring a program
CPU
Input module
Introduction to STEP 7
STEP 7 software
Machine to be
controlled
Output module
1-3