What'™s the reason for freezing the value of dynamic element?

What'™s the reason for freezing the value of dynamic element?

What’s the reason for freezing the value of dynamic element?
One problem has been occurred in my project,as when I disconnect the plc connection to PC(disconnect the communication connection) the values of dynamic element is freezed in latest value that has seen in dynamic element instead of zero value.
whether there is a way to see zero value (videlicet numerical value) when connection is disrupted.
connecting protocol is MODBUS.

This is a migrated post! Originally posted on 25.08.2009 by user shahramkh59. Please be aware that information can be outdated.