If multiple send FBs/receive FBs are simultaneously executed, the FBs do not function properly.
When there are multiple send FBs, do not execute two or more send FBs simultaneously. (Create a program that does not turn ON the I_START instructions for the send FBs simultaneously.)
When there are multiple receive FBs, do not execute two or more receive FBs simultaneously. (Create a program that does not turn ON the I_START instructions for the receive FBs simultaneously.)