States Of Command And Acknowledgment Counter - Siemens MOBY FC 56 Technical Description

Principle of controlling non-cyclic communication with command and
acknowledgment counter
Command counter
1*
DP-V1 telegram DP-V1 telegram
0
3
* Status of the counters after ASM startup or after an init_run_.
Figure B-1

States of command and acknowledgment counter

As you can see from the diagram above, a DP/V1 telegram triggers the change
from one defined state to the next. A new DP/V1 telegram is not permitted until
the next state is reached. A DP/V1 telegram is either a command to the ASM or
an acknowledgment from the ASM.
For this reason, it is important to tell the master whether a new DP/V1 telegram
can be executed. Each state is coded in 2 bits and counted up (as shown in the
diagram above) - thus the name state bits or state counters.
The state bits are sent cyclically to the master with PROFIBUS-DP. These
bits must be evaluated by the user program. When the state bit changes, a
new state (new state = old state + 1) is created. Only now can the next DP/V1
telegram be sent.
FC 56
J31069-D0155-U001-A0-7618
Programming MOBY-ASM on PROFIBUS-DP-V1
2
DP-V1 telegram
Acknowledgment counter
0*
3
2
1
B-3