Siemens simatic c7-621 Hardware Installation Manual page 130

Glossary
Process Image The signal states of the digital inputs and outputs are stored in the C7 CPU in
a process image. There are two process images: the process image input table
(PII) and the process image output table (PIQ).
The process image input table is read by the input modules before execution
of the user program.
The process image output table is transferred to the output modules by the
operating system at the end of the user program.
Programmable Programmable controllers (PLCs) are electronic controllers whose function is
Logic Controller
stored as a program in the CPU. The design and wiring of these devices
therefore does not depend on the controller function. The programmable
controller has the structure of a computer; it consists of a CPU with memory,
inputs and outputs and an internal bus system. The I/O and the programming
language are designed specifically for the requirements of control
engineering.
Programming Programming devices are essentially personal computers that are compact
Device and portable and suitable for use in industry. They are characterized by being
equipped with special hardware and software for SIMATIC programmable
controllers.
R
RAM Random access memory is a read/write memory in which each memory cell
can be addressed individually and can be changed. RAM memories are used
as data memories and program memories.
Reference Ground
–> Ground
Reference Potential to which from which the voltages of the connected circuits are
Potential referred.
S
Scan Cycle Time
The scan cycle time is the time required by the –> C7 to execute the –> user
program once.
Signal Module Signal modules (C7 I/Os) form the interface between the process and the C7.
There are digital input and output modules and analog input and output
modules.
Glossary-8
C7-621 / C7-621 AS-i Control Systems
C79000-G7076-C621-01