Siemens SIMATIC S7-300 Hardware And Installation Manual page 247

Backplane Bus
The serial backplane data bus supplies the power required by the modules. It is
also used by the modules for communication. The connection between the
modules is established by bus connectors.
Nesting depth
One block can be called from another by means of a block call. Nesting depth is
defined as the number of simultaneously called --> code blocks.
Interface, multipoint
--> MPI
Segment
--> Bus Segment
SFB
--> System function block
SFC
--> System function
Signal module
Signal modules (SM) form the interface between the process and the PLC. There
are digital and analog I/O modules (input/output module, digital or analog). analog
I/O modules (input/output module)
Slave
A slave can only exchange data on --> Master request.
Programmable controller
Programmable controllers (PLCs) are electronic controllers whose function is
saved as a program in the control unit. The configuration and wiring of the unit are
therefore independent of the function of the control system. The PLC has a
computer structure; it consists of the --> CPU (Central Processing Unit) with
memories, I/O modules and internal bus system. The I/Os and the programming
language are oriented to control engineering needs.
S7-300 Programmable Controller Hardware and Installation
A5E00105492-02
Glossary
13-13