Siemens Simatic Ident Function Manual page 139

Synchronization between command and acknowledgment counter
The command counter (CC_H/CC_L) and the acknowledgment counter (AC_H/AC_L) are
synchronized during a startup. The Ident device "AC_H/AC_L = 0" and "CC_H/CC_L = 1".
Initialization can be triggered both by the Ident device (by switching it on again) and by the
block (by means of "Init").
a
b
c
d
e
Figure A-2
Ident profile and Ident blocks, standard function for Ident systems
Function Manual, 10/2018, C79000-G8976-C387-04
CC_H/CC_L = 1, AC_H/AC_L = 0
Defined reset
"Write_Config" command to the Ident device
CC_H/CC_L = 2
AC_H/AC_L = 1
"Write_Config" acknowledgment from the Ident device
An error message occurs when a command is interrupted with "Write_Config" or "Init".
Time of startup (initiated by block)
Appendix
A.2 Cyclic data
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