Minimum Number Of Slaves For As-I Safety Applications - Siemens SIMATIC ET200SP Function Manual

Circuit diagram example
4.4 TIA Portal configuration
4.4.7

Minimum number of slaves for AS-i Safety applications

In a normal application, an AS-i network contains more than 5 AS-i slaves.
However, only 3 AS-i slaves are used for this example. In this case, the specifications in
EN 60262-2 (AS-i specification) for the minimum cycle time and minimum number of slaves
for AS-i Safety applications must be observed.
In an AS-i network with at least 5 different slave addresses in the numerical part of the
address, each safety component functions as intended. "In the numerical part of the address"
means that two slaves with the addresses 5A and 5B are counted here as 1 address, whereas
two slaves with the addresses 10A and 11B are counted as 2 addresses. For the count, it is
irrelevant whether or not these are safety slaves.
With less than 5 slave addresses, only restricted plant availability is possible, i.e. instead of an
"ON" signal in the safety transmission report, it is possible to switch back to the "OFF" safe
state, since the affected safety component cannot execute the report for the "ON" signal
quickly enough in the short bus cycle time. An "OFF" signal remains of course in the safe state
"OFF".
The TIA Portal outputs a corresponding warning message on compilation if not enough slaves
have been configured as AS-i slaves in the TIA project.
An AS-i Safety network usually still functions with fewer slaves. However, to avoid an
unwanted shutdown, the rules in the standard should be observed. The F-CM AS-i Safety
module offers a simple solution for this, without installing additional slaves.
Open the Properties dialog of the F-CM AS-i Safety, and navigate to the "Safe outputs" tab.
Select the vector group 0, and set the option "Activate output control". The F-CM AS-i Safety
module now generates an AS-i address internally. At the same time, an associated virtual
module (AS-i Safe Out Ctrl) is configured on the AS-i subnet, so that the AS-i master is
instructed to accept the additional AS-i address into the cyclic operation.
Repeat this step four more times, so that a total of 5 additional AS-i addresses are activated in
the F-CM AS-i module. These act as a "base load" in the AS-i network, irrespective of the
number of other AS-i modules in the AS-i network.
If your AS-i network has enough modules, you can correspondingly deactivate the output
control in the vector groups of the F-CM AS-i Safety.
When a vector group is activated, additional safe output bits are made available. Do not
interconnect these safe output bits in the safety program if the vector group is only used to
increase the number of slaves.
You can use the vector groups of the F-CM AS-i Safety and the associated safe output bits as
required to control safe AS-i output modules in the AS-i network (see e.g. Art. No.
3RK1405-1SG15-0AA2). In this case, you use the safe output bits in the safety logic of the
safety program in a similar way as for F-DQ modules of the ET 200SP. This Function Manual
does not include a detailed example for this application.
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Safety engineering with AS‑Interface in the SIMATIC ET 200SP, including typical circuit diagram
Function Manual, 08/2020, A5E44991382002A/RS-AB/002