Siemens Simatic S7-300, Руководство по аппаратному обеспечению и установке, Страница: 234 / 242

Glossary
S7-300 Programmable Controller Hardware and Installation
12-14
A5E00105492-01
Substitute value
Substitute values are configurable values which output modules transmit to the
process when the CPU switches to STOP mode.
In the event of an input access error, a substitute value can be written to the
accumulator instead of the input value which could not be read (SFC 44).
System diagnostics
System diagnostics is the term used to describe the detection, evaluation and
signaling of errors which occur within the programmable controller. Examples of
such errors are program errors or module failures. System errors can be displayed
with LED indicators or in STEP 7.
System function block
A System Function Block (SFB) is a --> function block integrated in the CPU
operating system. If required, it can be called in the STEP 7 user program.
System function
A system function (SFC) is an integrated --> Function of the CPU. It can be called
at any time in the STEP 7 user program.
System Memory
The system memory (RAM) is integrated on the central processing unit. System
memory contains the operand areas (e.g. timers, counters, memory bits) as well as
the data areas required internally by the --> operating system (e.g. buffers for
communication).
System state list
The system status list contains data describing the current status of an S7-300.
You can use it to gain an overview of the following at any time:
•
The S7-300 configuration
•
The current CPU configuration and the configurable signal modules
•
Current status and processes in the CPU and configurable signal modules.
Terminating resistor
The terminating resistance is used to avoid reflections on data links.
Time-of-day interrupt
--> Interrupt, Time-of-day
Timer
--> Timers, Principle