Siemens S7-300 System diagnostics, System function block, System status list, Timers

Glossary

System diagnostics

System diagnostics refers to the detection, evaluation and signaling of errors which occur within the PLC, Examples of such error/faults include: Program errors or failures on modules. System errors can be indicated by LEDs or in STEP 7.

System function

A system function (SFC) is a --> function integrated in the operating system of the CPU that can be called when necessary in the STEP 7 user program.

System function block

A system function block (SFB) is a --> function block integrated in the operating system of the CPU that can be called when necessary in the STEP 7 user program.

System memory

System memory is an integrated RAM memory in the CPU. System memory contains the address areas (e.g. timers, counters, flag bits) and data areas that are required internally by the operating system (for example, communication buffers).

System status list

The system status list contains data that describes the current status of an S7-300. You can always use this list to obtain an overview of:

•The configuration of the S7-300

•the current CPU configuration and configurable signal modules

•the current status and processes in the CPU and in configurable signal modules.

Terminating resistor

The terminating resistor is used to avoid reflections on data links.

Timer

See Timers

Timers

Timers are part of CPU system memory. The content of timer cells is automatically updated by the operating system, asynchronously to the user program. STEP 7 instructions are used to define the precise function of the timer cell (for example, on-delay) and to initiate their execution (for example, start).

TOD interrupt

See Interrupt, time-of-day

CPU 31xC and CPU 31x, Technical data Manual, Edition 08/2004, A5E00105475-05

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