Siemens SIRIUS 3RK3 - Diagnosis Using AS-Interface (CTT2 Protocol); Diagnostics Concept Using the CTT2 Protocol; Diagnostics Using the CTT2 Protocol

7.6 Diagnosis using AS-Interface (CTT2 protocol)
7.6.1 Diagnostics concept using the CTT2 protocol
For the 3RK3 central units with AS-interface, the diagnostics concept of the MSS 3RK3 Basic is
supplemented to include diagnostics of elements via AS-Interface using the CTT2 protocol. For
this purpose, the MSS 3RK3 simulates a CTT2 slave, which is interconnected in the logic. The
diagnostics concept using the CTT2 protocol is shown in the following graphic: The device
messages result in an entry in the cyclic data, the message data. The acyclic data can then be
read out using a command. In these acyclic data, all elements are entered with their pending
messages.
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Figure 7-4 Diagnostics concept of MSS 3RK3 with AS-i interface using CTT2
7.6.2 Diagnostics using the CTT2 protocol
Diagnostics over an AS‑i CTT2 channel provides access to the elements that have an error or
whose safety sensor has been triggered. Device diagnostics using AS‑i is possible with a
simulated AS‑i slave of type CTT2. This is able to process AS‑i frames of type "Combined
Transaction Type 2."
Because both the cyclic and the acyclic "CTT2 data" are transmitted over the same CTT2 channel,
the cyclic CTT2 data transmission from the AS‑i master is interrupted for transmission of the
acyclic CTT2 data and resumed by the AS‑i master automatically after acyclic data transmission
has been completed.
Cyclic CTT2 data transmission
The cyclic CTT2 data transmission provides 8 bytes of input data and 8 bytes of output data per
AS‑i standard slave, which are cyclically exchanged over the CTT2 channel between the AS‑i
master and the AS‑i slaves. Message data are sent by the AS‑i slave to the AS‑i master and control
data are sent by the AS‑i master to the AS‑i slave.
For the simulated CTT2 slave of the MSS 3RK3, the message data consist of 2 bytes of diagnostics
data and 6 bytes of freely interconnectable signals that can be interconnected in the logic via
terminals. The diagnostic data signal the status and the operating state of the MSS 3RK3 to a
higher-level control.
The MSS 3RK3 can be acknowledged with RESET via the control data.
Diagnostics / service
7.6 Diagnosis using AS-Interface (CTT2 protocol)
SIRIUS 3RK3 Modular Safety System
298 Equipment Manual, 07/2020, NEB926253002000/RS-AC/006