What should you watch out for when using the fail-safe communication blocks of S7 F Systems Lib V1.3 SP2 and higher?
With version V1.3 SP2 of the "S7 F Systems Lib" the blocks F_RCVBO, F_RCVR and F_RDS_R have received a new input parameter - "COMMVER_USED" - with which the compatibility mode can be set. This input parameter is set by default to "1".
Behavior with "COMMVER_USED" = 1
- This mode does not support communication with blocks from older versions of the S7 F Systems Lib (< V1.3 SP2).
- The communication is not affected by a brief connection interruption as long as the duration of the interruption is less than the set F monitoring time (value at the "TIMEOUT" input parameter.
- In the case of a communication overload, with this setting there might be sequence number errors that lead to an interruption of the communication and switching to the configured substitute values via the
F communication blocks.
More information on the topic is available in the entry entitled How can you determine the quantity framework of the communication instances (PBC) for PCS 7 automation systems?.
Behavior with "COMMVER_USED" = 0
- This mode supports communication with blocks from older versions of the S7 F Systems Lib (< V1.3 SP2).
- The communication can be aborted by a brief connection interruption even if the duration of the interruption is less than the set F monitoring time. If there is abortion of the F communication, there is a switchover to the configured substitute values.
- In this mode, a communication overload does not lead to an abortion of the F communication.
More information about F communication blocks and the "COMMVER_USED" input parameter is available in the manual entitled SIMATIC Industrial software S7 F/FH Systems - Configuring and Programming in the section "F-Blocks for F-Communication between F-CPUs".