Value Status - Siemens SIMATIC ET 200SP Manual

Assigning parameters / Setting the address space
6.3 Address space
Note
Use of the error acknowledgment bit of a safe AS-i output
The values in the PROFIsafe process output image have Safety Integrity Level SIL 3. In
addition to the switching states, a control unit can send out two different auxiliary signals to a
safe AS-i output: AUX1 and AUX2. These auxiliary signals are not safety-related signals.
You can use the auxiliary signals for error acknowledgement in the evaluation unit. For
technical reasons, these error acknowledgment bits are mapped in the safe process output
image. If error acknowledgment bits are sent to a safe AS-i output, the
Manager configuration tool is unable to detect that the error acknowledgment bits are not
safe. This means: No warnings or faults will be output for it when the safety application is
generated. The user is responsible for the correct processing of these signals in the safety
application.
6.3.2

Value status

Properties
For each input signal and output signal, the F-CM AS-i Safety ST module provides
information about the signal's validity, i.e., the "value status". Like the input signal, the value
status is stored in the process image.
Value status for the digital input and output modules
The value status is binary supplementary information of a digital input or output signal. It is
entered in the process input image simultaneously with the process signal. The value status
provides information regarding the validity of the input or output signal.
The value status is influenced by the following:
● Code sequence errors, e.g, caused by a permanent fault on the AS-i bus, wiring error,
etc.
● Missing safe AS-i input slaves
● Channel faults
● Replacement of a safe AS-i slave by a non-safe AS-i slave
● Discrepancy error
● Sequence error
Value status = 1: A valid process value is output for the channel.
Value status = 0: A substitute value is output for the channel or the channel is deactivated.
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Fail-safe Module F‑CM AS‑i Safety ST (3RK7136‑6SC00‑0BC1)
Manual, 03/2017, A5E03957059020A/RS-AB/002
STEP 7
or SIMATIC