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Rules for Failsafe Operation of an S5-95F
18.13.7 Triggering Edge for OB3 Interrupts
Safety Note
Execution of the interrupt service routine in OB3 can be initiated by a) a falling edge, b)
a rising edge or c) a falling or rising edge at a software interrupt input. The edge(s) to
trigger execution of OB3 must be specified with COM 95F.
Always choose a falling edge to trigger an interrupt. You should deviate from this only in
very special cases, and only after consulting with the responsible authority.
If the appropriate parameters are assigned, the S5-95F responds to a signal edge change at an
interrupt DI as follows:
•
On the falling edge as soon as a signal change from 1 to 0 is detected in one subunit .
On the rising edge when a signal change from 0 to 1 is detected in both subunits .
•
Special Feature of Interrupt DIs with OB1-Oriented Discrepancy Time
In systems with basic units 095-8FA02 you can also use the interrupt DIs with an OB1-oriented
discrepancy time.
To ensure detection of a continuous 1 fault by the S5-95F, the duration of the "0" and "1" signal
states must be at least: parametrized discrepancy time + one OB1 cycle .
18.13.8
Measures for Securing the User Program Against Errors
In safety mode, the user program must be stored on an EPROM submodule. The EPROM
submodules for the two subunits are identical.
Safety Measures for the User Program Provided by the S5-95F
The S5-95F examines the identity and integrity of the programs in subunits A and B in its RESTART
routine.
The S5-95F goes to STOP when
•
The two subunits' EPROM submodules contain different programs
•
The EPROMs were replaced without execution of an overall reset and the EPROMs previously in
the subunits had a different system ID number
•
Loaded standard function blocks were damaged or manipulated
Safety Measures Against Systematic Programmer Errors
The COM 95F software package contains an acceptance tool with which the user program can be
checked for programmer errors. The tool can detect systematic programmer errors and programmer
hardware failures (refer to the COM 95F Manual for details).
18-28
S5-95F
EWA 4NEB 812 6210-02
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