Chapter 12. DiagnosticsGFK-2224Q January 2017 21912.7 Monitoring the FT Output of the COMMREQ Function Block.The COMMREQ function block indicates its status through its FT output:(Enable )-------------(Command Block address)(Rack/Slot Location ofthe Ethernet Interface)(Task value)---- Function Faulted (logic)COMMREQIN FTSYSIDTASK- CommReq DeliveredFigure 90: Monitoring FT Output in COMMREQ Function BlockIf after executing a COMMREQ Function, the FT Output is ON, there is a programming error in one or more ofthe following areas.▪ Invalid rack/slot specified. The module at this rack/slot is unable to receive a COMMREQ Command Block.▪ Invalid Task ID. This value should always be 65536 decimal (10000H) for the CPU Ethernet daughterboard,or 0 decimal (0000H) for the Ethernet module.▪ Invalid Data Block length (0 or greater than 128).This output also may indicate that no more COMMREQ functions can be initiated in the ladder program until theEthernet Interface has time to process some of the pending COMMREQ functions.If the FT Output is set, the CPU did not transfer the Command Block to the Ethernet Interface. In this case, theother status indicators are not updated for this COMMREQ. The Ethernet Interface is unable to return aCOMMREQ Status Word to the PLC logic application.12.8 Monitoring the COMMREQ Status WordEvery COMMREQ Command Block instruction specifies a 1-word memory address to receive status informationabout the execution of the command.Before executing a COMMREQ for the Ethernet interface, the application program logic should the associatedstatus word zero (for example, using a MOVE Word instruction). After executing a COMMREQ, the programshould monitor its status word. If the status word is updated to a one (1), the command has been processedsuccessfully. If the status word is updated to a value other than 1, an error has occurred. Any data returned bythat command should not be used until the problem is corrected and the status word indicates success. It iscritical to monitor the COMMREQ status word for each COMMREQ function. .If after executing a COMMREQ function, the COMMREQ status word is zero (0), the success Output is ON and theFT Output is OFF, the Command Block has been sent to the Ethernet Interface, but no status has been returned.If this condition persists, check the Controller Fault Table for information.
