Connecting Sensors/Actuators7.3 Safe programmable logic (SPL)05.087-225© Siemens AG 2008 All Rights ReservedSINUMERIK 840D sl/SINAMICS S120 SINUMERIK Safety Integrated (FBSI sl) – 05.2008 EditionClearing the external SPL outputs for SPL system errorsIf communications between the NCK and PLC with reference to the SPL crosswisedata comparison, are interrupted, then all external SPL output signals($A_OUTSE/$A_OUTSEP) are deleted with a delay of 5 s.This state occurs if no data exchange or crosswise data comparison occurs be-tween the NCK and PLC for one second. This is due to the fact that– the one second limit of the user cycle limit in the PLC (OB1 cycle) was ex-ceeded.– a system error has occurred. The NCK or PLC system software no longer runsdue to a system error – therefore interrupting communications.Behavior of the NCKThe specified timer of 5 s is started if Alarm 27092 ”Communication interrupted forcrosswise data comparison NCK–SPL, error detected by %1” is initiated. This isindependent of which component (NCK or PLC) interrupted the alarm.The system variable $A_STATSID, bit 29 = 1 is used to indicate to the SPL userthat this timer has been started. This means that he has a possibility of initiatingplant/system–specific actions before the system deletes (clears) the output.After this time has expired, the system deletes the external SPL outputs. The sta-tus variable $A_STATSID, bit 29 remains set. When reading–back the external out-puts in the NCK–SPL via the system variable $A_OUTSE, ”0” is read correspond-ing to the actual output status.Behavior of the PLCIf, on the PLC side, it is detected that the communication timeout has been ex-ceeded, then a timer is started with 5 s.After this time has expired, the PLC goes into Stop (by calling an SFC46). Thisstate can only be exited using a power on.After the 5 s timer has expired, the PLC outputs its own message for diagnosticpurposes. At the same time, an entry with the same significance is located in thediagnostics buffer.Using the status signal DB18.DBX119.5, the SPL programmer and the NCK is pro-vided with the information that the timer was started. This means that he has thepossibility of initiating system–specific actions before the PLC goes into the stopcondition.NoteIn order to achieve the shortest possible response time, the system variable$A_STATSID, bit 29 and the status signal DB18.DBX119.5 must be evaluated inthe SPL in order to bring, as far as possible, the SPL–SGA into a safe state(cleared SPL–SGA).
