Logix5000 Controllers General Instructions - SLAC Confluence

174 Input/Output Instructions (MSG, GSV, SSV, IOT)Description:The GSV/SSV instructions get and set controller system data that isstored in objects. The controller stores system data in objects. There isno status file, as in the PLC-5 processor.When enabled, the GSV instruction retrieves the specified informationand places it in the destination. When enabled, the SSV instructionsets the specified attribute with data from the source.When you enter a GSV/SSV instruction, the programming softwaredisplays the valid object classes, object names, and attribute names foreach instruction. For the GSV instruction, you can get values for all theavailable attributes. For the SSV instruction, the software displays onlythose attributes are allowed to set (SSV).ATTENTIONUse the GSV and SSV instructions carefully. Making changes to objects may causeunexpected controller operation or injury to personnel.You must test and confirm that the instructions don’t change data that you don’twant them to change.The GSV and SSV instructions write or read past a member into other members of atag. If the tag is too small, the instructions don’t write or read the data. They log aminor fault instead.Example 1Member_A is too small for the attribute. So the GSV instruction writes the lastvalue to Member_B.Example 2My_Tag is too small for the attribute. So the GSV instruction stops and logs a minorfault.Publication 1756-RM003I-EN-P - January 2007