With the CPUS7315F, ET200S, and fail-safe DI / DO modules, you will call the OB35 fail-safe program. Also, you have accepted the default settings for all monitoring times and are willing to receive the "communication failure" message. OB35 is set to 100 milliseconds by default. You have set the F monitoring time of the F I / O module to 100 milliseconds so that the I / O module is addressed at least once every 100 milliseconds. However, since the OB35 is called every 100 milliseconds, a communication failure occurs. To ensure that the scan interval of the OB35 differs from the F monitoring time, make sure that the F monitoring time is greater than the scan interval of OB35.

S7 distributed security system, until the V5.2SP1 and 6ES7138-4FA00-0AB0,6ES7138-4FB00-0AB0,6ES7138-4CF00-0AB0 will appear this problem. In the new module, the F monitoring time is set to 150 milliseconds.