Siemens SIMATIC S7-300 Series Reference Manual page 182

Glossary
Process image
The process image forms part of ³ CPU system memory. The signal states of
the input modules are written to the input process image at the start of the cyclic
program. At the end of the cyclic program, the signal states in the output process
image are transferred to the output modules.
Process Interrupt
A process interrupt is generated by respective modules, triggered as a result of
specific hardware events. The process interrupt is reported to the CPU. An
assigned OB is then processed, according to the interrupt priority³.
Product version
The product version differentiates between products which have the same order
number. The product version is increased with each upwardly compatible
function extension, production-related modification (use of new components) or
bug-fix.
PROFIBUS-DP
Digital, analog and intelligent modules and a wide range of field devices to EN
50170, Part 3, e.g. drives or valve blocks, are distributed local to the local
process by the PLC - across distances of up to 23 km.
The modules and field devices are connected to the programmable controller via
the PROFIBUS-DP fieldbus and addressed in the same way as centralized I/Os.
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
programmable controller has the structure of a computer; it consists of the ³
CPU (central module) with its memory, I/O modules and an internal bus system.
The I/Os and the programming language are oriented to control engineering
needs.
Programming device
Programming devices are essentially personal computers which are compact,
portable and suitable for industrial applications. They are equipped with special
hardware and software for SIMATIC programmable controllers.
Glossary-12
PLC S7-300, CPU Specifications CPU 312 IFM to CPU 318-2 DP
A5E00111190-01