Chapter 6. Service Request FunctionGFK-2950C February 2018 2836.6 SVC_REQ 5: Change Background Task Window Mode andTimer ValueUse SVC_REQ 5 to change the Background Task window mode and timer value. The change takesplace during the next CPU sweep after the function is called.SVC_REQ 5 executes unless a mode other than 0 (Limited) or 2 (Run-to-Completion) is selected.The parameter block has a length of one word.6.6.1 To disable the Background Task window:Enter SVC_REQ 5 with this parameter block:Address High Byte Low ByteAddress 0 06.6.2 To enable the Background Task window mode:Enter SVC_REQ 5 with this parameter block:Address High Byte Low ByteAddress Mode 0 = Limited2 = Run to Completion1ms value 255msSVC_REQ 5 ExampleWhen enabling contact #FST_SCN is set in the first scan, the MOVE function establishes a value of20ms for the Background task window, using a parameter block beginning at %P00050. Later in theprogram, when input %I00500 transitions on, the state of the Background task window toggles onand off. The parameter block for all three windows is at location %P00051. The time for theBackground task window is the third value in the parameter block returned from the Read WindowValues function (function #2); therefore, the location of the existing window time for the Backgroundwindow is %P00053.
