Siemens SIRIUS M200D Manual page 21

Extended cyclic process image:
CTT2 transfer is used for continually transferring 4 bytes between the AS-i master and slave,
in both directions.
Note
In the AS-i system, this generally involves analog data; however, the term "transparent data"
is more accurate for the M200D.
Data set transfer:
CTT2 transfer is used for transferring data sets between the AS-i master and slave. The data
sets are only transferred when triggered to do so. While (acyclic) data set transfer is in
progress, (cyclic) transfer of the extended process image is interrupted.
M200D AS-Interface Standard
Manual, 08/2014, A5E02548958A/RS-AA/004
Product family
2.4 Internal design
21