Siemens SIMATIC S7 Manual page 58

CPU
CRC
Cycle Time
Cyclic Program Processing
D
Data Block (DB)
Data Type
Default Setting
Diagnostic Buffer
Diagnostic Event
Diagnostic Functions
Download
F
Function Block (FB)
H
Hardware
MODBUS / TCP communication via the integrated PN interface of the CPU
2XV9450-1MB02; Manual edition 2.1
Central processing unit of the S7 programmable logic controller with
control and arithmetic unit, memory, operating system, and interfaces to
I/O modules.
Cyclic Redundancy-Check = Checksum which guarantees a high
probability of error recognition.
The cycle time is the time the PLC needs to execute the user program
once.
In cyclic program processing, the user program is executed in a
constantly repeating program loop, called a cycle.
These are blocks containing data and parameters with which the user
program works. Unlike all other blocks, data blocks do not contain
instructions. They are subdivided into global data blocks and instance
data blocks. The data held in the data blocks can be accessed
absolutely or symbolically. Complex data can be stored in structured
form.
Data types allow users to define how the value of a variable or constant
is to be used in the user program. They are classified into elementary
and structured data types.
The default setting is a basic setting which is always used if no other
value is specified.
Every PLC has a diagnostic buffer, in which detailed information on
diagnostic events are stored in the order in which they occur.
Diagnostic events are, for example, errors on a module or system
errors in the PLC, which are caused by, say, a program error or by
operating mode transitions.
The diagnostics functions cover the entire system diagnosis and include
detection, analysis and reporting of errors within the automation
system.
Downloading means loading objects (e.g. code blocks) from the
programming device into the load memory of the PLC.
Function blocks are components of the user program and, in
accordance with the IEC standard, are "blocks with memory". The
memory for the function block is an assigned data block, a so called
"instance data block". Function blocks can be parameterized but can
also be used without parameters.
Hardware is the term given to all the physical and technical equipment
of a PLC.
Glossary - 2