Siemens SIMATIC S5-115U, User Manual

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Technical Description S5-115U Manual
2.5 Operating Modes
Use the mode selector to set the "STOP" (ST) or "RUN" (RN) mode. The CPU executes the
"RESTART" mode automatically between "STOP" and "RUN".
2.5.1 STOP Mode
The program is not scanned in STOP mode. The values of the timers, counters, flags and process
images that were current when the CPU went into the STOP state are maintained. Output
modules are disabled (signal state "0"). The BASP (output disable) LED lights up. The BASP signal
is cancelled only after OB21 or OB22 (RESTART) have been processed.
2.5.2 Restart Characteristics
Everything that takes place between
•
a STOP RUN transition (manual cold restart) or
• a POWER UP RUN transition (automatic cold restart after power up)
is referred to as restart characteristics.
Two phases can be distinguished during restart:
•
The cold restart routine (PLC cannot be directly influenced)
• The actual RESTART (PLC characteristics can be controlled in RESTART OBs (OB21 and OB22)).
Cold Restart Routine
The following applies while the CPU runs the cold restart routine:
•
The BASP LED lights up;
- The status of the error LEDs remains unchanged during manual cold restart
- The error LEDs light up momentarily during automatic cold restart after power up
• Outputs display signal "0" if all output modules are disabled
• All inputs and outputs in the process I/O image display signal "0"
• Scan time monitoring is inactive.
During the cold restart routine, the processor ascertains the configuration of the I/O modules and
stores this information. This procedure is described in detail in the following.
To establish the configuration of the I/O modules, the processor checks the full address area of
the input/output modules word by word. If it addresses a module over an I/O word (=2 bytes),
the processor "notes" this word by setting the bit allocated to it in a special memory area called
the system data area. This bit is only set by the processor if both I/O bytes of an I/O word are
addressable.
The processor uses a system data word (SD) to check 16 I/O words (=32 I/O bytes).
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