4.2.2. gc_Extension( )

The gc_Extension( ) function and corresponding GCEV_EXTENSION event is primarily used to support the Continuity Check feature.

For the GCEV_EXTENSION event, the extevtdatap field of the METAEVENT structure is a pointer to an EXTENSIONEVTBLK structure. The ext_id member of EXTENSIONEVTBLK can be:

• S7_EXT_CONTCHECK - Indicating the beginning of a Continuity Check.
• S7_EXT_CONTCHECK_END - Indicating the end of a Continuity Check

The parmblk field of the EXTENSIONEVTBLK structure contains additional information. The parmblk field is of type GC_PARM_BLK and contains only a GC_PARM_DATA structure. The set_ID of GC_PARM_DATA is S7SET_CONTCHECK, and the parm_ID is S7PARM_CONTCHECK_TYPE. The parm_data_size is sizeof(int).

For an inbound Continuity Check request, the value of this parameter is S7RV_CC_INBOUND. See Section 5.10.1, Inbound Continuity Check for more information.

For an outbound, out-of-call Continuity Check request, the application can use the gc_Extension( ) function with an ext_id of S7_EXT_REQUESTCONTCHECK. See Section 5.10.2, Outbound Continuity Check for more information.

For an outbound, in-call Continuity Check request, the application must use the gc_MakeCall( ) function. See Section 4.3.8, gc_MakeCall( ) for more information.

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