jQuery Grid Plugin - jqGrid

Hi!, I need a way to send a param to the server to indicate if Find button was clicked. _search param seems to be the right one but does not work as I need.

When Find button is clicked the grid send this data:

_search:true , nd:1304967922522 , rows:30 , page:1 , sidx:cpdId , sord:asc , filters:{"groupOp":"AND","rules":[{"field":"cpdId","op":"le","data":"13"}]}

And if after insert a filter, another action throws an ajax request, the grid send this data:

_search:true , nd:1304968373713 , rows:30 , page:1 , sidx:cpdId , sord:desc , filters:{"groupOp":"AND","rules":[{"field":"cpdId","op":"le","data":"13"}]}

_search seems to indicate if a filter is present or not.

I'm using jqgrid 3.8.2.

Thanks in advance!

Héctor