Siemens SIRIUS 3RK3 - Acyclic Data Transmission with Function Block

7.6.4 Acyclic data transmission with function block
The process of transferring CTT2 data from the CPU to AS-i master is dependent on the master.
The sequence is described below by way of example based on the DP/AS-i link Advanced. If you
are working with SIEMENS AS-i masters and SIMATIC S7 controllers, FC ASI_3422, for example,
o󹪜ers a user-friendly command interface.
Note
This FC ASi_3422 is not supported by all SIEMENS AS-i masters. You will 󹪝nd additional
information in the documentation of the FC ASi_3422.
If you are not using the FC ASi_3422, refer to the documentation of the master used and the
following chapter on CTT2..
Command interface block FB ASI_CTRL for AS-i master
Calling the command interface block FB ASI_CTRL enables you to both transfer commands and
accept response data. The FB ASI_CTRL administers the calls Write_data_record and
Read_data_record autonomously
When the command interface is called using command 44
H
, a byte string can be used to send a
CTT2 request to the AS-i master. The master forwards the string bytes to the AS-i slave address
speci󹪝ed in the transmit bu󹪜er. The AS-i master determines the number of string bytes to be sent
to the AS-i slave (number depends on the data set to be transferred) on the basis of byte 2 of the
transmit bu󹪜er (number of string bytes).
The addressed AS-i slave responds to the CTT2 request with a CTT2 response. The AS-i master
communicates this response as a byte string in the receive bu󹪜er. The structure of the CTT2
request or CTT2 response (code, index, etc.) begins with string byte 1 in each case and is not
dependent on the master.
The extended process image with the addressed AS-i slave is not transferred while string
transfers to the AS-i are taking place.
Depending on the type of protocol, the process of transmitting a data set to a slave may take up
to 19 s:
• Read DS3: up to 17 s
• Write DS3: up to 2 s
Reference
You will 󹪝nd further details in the Internet (http://support.automation.siemens.com/WW/
view/en/22710305).
Diagnostics / service
7.6 Diagnosis using AS-Interface (CTT2 protocol)
SIRIUS 3RK3 Modular Safety System
302 Equipment Manual, 07/2020, NEB926253002000/RS-AC/006