Difference Between Dynamic/Static Signals - Siemens SINUMERIK 880 SW 6 Planning Manual

01.93
Basic signals in the flag area
Certain flag bytes (FYs) contain the basic signals for the PLC program. These comprise, for
example, ready signals, initial setting signals, interrupt signals and alarm signals. The PLC
operating system informs the PLC user program of the system condition by means of the basic
signals.
The flag area encompasses the flag bytes FY 0 to FY 255. The basic signals are contained in
FY 0 to FY 24. The area FY 25 to FY 255 can be utilized by the user program. Certain periph-
eral conditions that are explained with the description of the flag area must, however, be taken
into account here (see Section "Provision of Basic Signals").

1.2.2.5 Difference between dynamic/static signals

Signals are either dynamic or static.
Static signals are set or reset only by communication partners (PLC user program and, e.g.,
the NC). Static signals retain their value for several PLC cycles provided that it is not changed
by one of the communication partners.
Dynamic signals, on the other hand, are reset by the PLC operating system after one PLC
cycle. Dynamic signals are passed only to the PLC, that is to say from the NC, operator panel,
COM and the peer PLC.
Most dynamic signals are also available in the form of static signals.
1.2.3 Reaction to interrupt and alarm signals
A differentiation is made between interrupts triggered by machine signals (hardware interrupts)
and program interrupts triggered by the PLC operating system owing to alarm signal edge
changes (also see "Interrupt-generating I/O devices" Section).
Hardware interrupts
Hardware interrupts can be processed only in a special PLC mode, referred to as the special
mode. The PLC operating system depicts the interrupt-generating signals (see Section 1.4.3)
in the flag area so that the image showing the interrupt-generating signals reveals which signal
triggered the interrupt. Then the organisation block for interrupt processing OB 2 is called as
the user interface.
The signals that generate hardware interrupts can be masked. The edge of the interrupt-
generating signal that triggers the interrupt is determined by machine data.
Program interruption by alarm signal edge changes
The user can define certain input bytes as alarm bytes by means of machine data. The signals
depicted there trigger program interrupts.
Unlike the hardware interrupts, program interrupts are not triggered directly by the signals in
this case. The PLC operating system periodically updates the image of the incoming alarm
signals in the alarm bytes (about every 10 ms). OB 3 is activated if an edge change is detect-
ed in an alarm byte.
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1) If using a SIMATIC S5-155U, refer to SINUMERIK 880 with S5-155U, Difference Description to PLC 135 WB in
this context
© Siemens AG 1991 All Rights Reserved
SINUMERIK 880 (PJ)
1)
6ZB5 410-0HE02
1 General Overview
1.2.2 PLC program structure
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