请问老师：

机械臂及拧丝单元相关配套实验提供的练习答案项目中，子程序ExciseScrewCtrlManualScl中第63行，#statErrorUserCleared条件何时满足，我在程序中没有找到此句=1的语句，有点不理解此行的作用，请老师指点？？

包含此行的完整程序如下，行末有中文标记

//Check if FB is disabled

IF #axis = #AXIS_SCREW

    AND #mode = #MODE_MANUAL

THEN

    IF NOT #enable

        AND #statEnableOld

    THEN

        //TODO : Add functionality after disabling functionality, e.g. closing connections

        //--------------------------------------------------------------------------------

        //Error outputs are reset with falling edge of enable input

        #statErrorUserCleared := FALSE;

        #statErrorAutoCleared := FALSE;

        #error := FALSE;

        #status := #STATUS_NO_CALL;

        #errorID := #ERRORID_NO_ERROR;

        #statusID := #STATUSID_NO_FUNCTIONBLOCK;

        //Enable and busy are reset with falling edge of enable input

        #valid := FALSE;

        #busy := FALSE;

        //Set old value of enable for edge detection and end execution

        #statEnableOld := #enable;

        #instSinaPosScrew.ExecuteMode := false;

        RETURN;

        //Check if FB is enabled

    ELSIF #enable

        AND NOT #statEnableOld

    THEN

        //TODO: Initialize values after enabling FB, e.g. set state machine to initial state

        //-----------------------------------------------------------------------------------

        #instSinaPosScrew.HWIDSTW := #screwHwId;

        #instSinaPosScrew.HWIDZSW := #screwHwId;

        //Busy is set at rising edge of enable input

        #busy := TRUE;

        //Set status for first call

        #status := #STATUS_FIRST_CALL;

        //Set old value of enable for edge detection and end execution

        #statEnableOld := #enable;

        RETURN;

        //Check if user cleared error in FB occurred

    ELSIF #statErrorUserCleared                         //此行的条件何时=1，程序中没找到？？？？？？？

    THEN

        #busy := FALSE;

        //Set old value of enable for edge detection and end execution

        #statEnableOld := #enable;

        //No set of status necessary, because status already set when error occured

        RETURN;

        //Check if function block is disabled

    ELSIF NOT #enable

    THEN

        #busy := FALSE;

        #status := #STATUS_NO_CALL;

        //Set old value of enable for edge detection and end execution

        #statEnableOld := #enable;

        RETURN;

    ELSE

        //Detect edge for disabling

        #statEnableOld := #enable;

    END_IF;