Allen-Bradley Logix5000 Reference Manual page 196

Chapter 4 Input/Output Instructions (MSG, GSV, SSV, IOT)
196
ATTENTION: Use the GSV and SSV instructions carefully. Making changes to objects
may cause unexpected controller operation or injury to personnel.
You must test and confirm that the instructions don't change data that you don't
want them to change.
The GSV and SSV instructions write or read past a member into other members of a
tag. If the tag is too small, the instructions don't write or read the data. They log a
minor fault instead.
Example 1
Member_A is too small for the attribute. So the GSV instruction writes the last
value to Member_B.
Example 2
My_Tag is too small for the attribute. So the GSV instruction stops and logs a minor
fault.
Rockwell Automation Publication 1756-RM003N-EN-P - October 2011