SmartPLC SafeLine AC4S with fieldbus interfaces
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8.5
Data exchange between standard PLC and fail-safe PLC
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Standard PLC and fail-safe PLC of AC4S use a separate hardware. Data between the two areas is
therefore exchanged via a special memory area to which both PLCs can access independently from
each other.
The programmer can organise the data exchange between the areas via the CODESYS mechanism of
the logical exchange variables.
► Familiarise yourself with the following CODESYS functions!
GVL for logical exchange of data
→ Online help > Add-Ons > CODESYS Safety > Device topology > Logical I/Os >
GVL for logical exchange
Logical I/O for data exchange with the main controller
→ Online help > Add-Ons > CODESYS Safety > Device topology > Logical I/Os >
Logical I/O for data exchange with the main controller
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8.5.1
Remarks about the use of exchange variables
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The variable values between Standard PLC and fail-safe PLC are transferred as non-safe
data.
► Do not implicitly use non-safe variable values for safe functions.
If Standard PLC is in STOP state, the declared exchange variables for the data transfer
towards the safety PLC are written with the replacement value "0".
► Always transfer safe information created in the fail-safe area to the standard area
unchanged.
The signal can then be further processed (e.g. negation) in the standard area
