Siemens SIMATIC ET 200SP Manual page 37

Evaluation unit
The evaluation unit reads the safety-related control commands ON or OFF on the AS-i bus
and passes corresponding switching commands, e.g., to switching contacts. In case of error,
e.g., communication error on the AS-i bus, the evaluation unit switches off. The evaluation
unit is integrated in the safe AS-i output module to which, for example, drive contactor coils
are connected. The evaluation unit behaves as a passive unit in the AS-i communication.
The master does not detect the evaluation unit and does not call it. The evaluation unit
monitors the communication of the AS-i address of the control unit and reacts to its safety-
related control signals.
You set the AS-i address (see Section "Control unit") the evaluation unit is to monitor.
You can set multiple evaluation units to the same address so that a control unit can control
multiple safe output modules simultaneously.
NOTICE
Bus cycle time for safe AS-i outputs
An evaluation unit requires a minimum AS-i bus cycle time. Ensure that at least 5 AS-i
addresses are present on the AS-i bus. Otherwise, the control unit goes to error state.
When A/B slaves are used, at least 5 different numerical AS-i addresses must be present.
That is, a combination of slave addresses 1A and 1B count as 1 numerical address.
The F-CM AS-i Safety ST module does not have a monitoring function for this configuration
rule.
Fail-safe Module F‑CM AS‑i Safety ST (3RK7136‑6SC00‑0BC1)
Manual, 03/2017, A5E03957059020A/RS-AB/002
5.2 Safety-related communication with AS-Interface
Configuring
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