GE PACSystems RXi User Manual

Chapter 7. CPU Program Data128 PACSystems* RXi Distributed IO Controller User Manual GFK-2816F7.2.2 Bit (Discrete) ReferencesType Description%I Represents input references. %I references are located in the input status table, which storesthe state of all inputs received from input modules during the last input scan. A referenceaddress is assigned to discrete input modules using your programming software. Until areference address is assigned, no data will be received from the module. %I memory is alwaysretentive.%Q Represents physical output references. The coil check function checks for multiple uses of %Qreferences with relay coils or outputs on functions. You can select the level of coil checkingdesired (Single, Warn Multiple, or Multiple).%Q references are located in the output status table, which stores the state of the outputreferences as last set by the application program. This output status table’s values are sent tooutput modules at the end of the program scan. A reference address is assigned to discreteoutput modules using your programming software. Until a reference address is assigned, nodata is sent to the module. A particular %Q reference may be either retentive or non-retentive.%M Represents internal references. The coil check function of your programming software checksfor multiple uses of %M references with relay coils or outputs on functions. A particular %Mreference may be either retentive or non-retentive.%T Represents temporary references. These references are never checked for multiple coil useand can, therefore, be used many times in the same program even when coil use checking isenabled—this is not a recommended practice because it makes subsequent trouble-shootingmore difficult. %T may be used to prevent coil use conflicts while using the cut/paste and filewrite/include functions. Because this memory is intended for temporary use, it is cleared onStop-to-Run transitions and cannot be used with retentive coils.%S%SA%SB%SCRepresent system status references. These references are used to access special CPU datasuch as timers, scan information, and fault information. For example, the %SC0012 bit can beused to check the status of the Controller Fault table. Once the bit is set on by an error, it willnot be reset until after the sweep.■ %S, %SA, %SB, and %SC can be used on any contacts.■ %SA, %SB, and %SC can be used on retentive coils -(M)-.Note: Although the programming software forces the logic to use retentive coils with %SA,%SB, and %SC references, most of these references are not preserved across powercycles, regardless of the state of the Energy Pack.%S can be used as word or bit-string input arguments to functions or function blocks.%SA, %SB, and %SC can be used as word or bit-string input or output arguments to functionsand function blocks.For a description of the behavior of each bit, refer to Section 7.7, System Status References.%G Represents global data references. These references are used to access data shared amongseveral control systems.Note: For details on retentiveness, refer to Section 7.5 Retentiveness of Logic and Data.