Web Forms :: Check Validation When Save Button Pressed?

I am CustomValidator to vlidate some data.There are 3 static buttons and some dynamically creating buttons in that page. I just need to check validation when I press the save button.For all other button click I do not want to call the validation. How do I tell that in the Validation function?

<asp:CustomValidator ID="CustomValidator1" runat="server"
ErrorMessage="CustomValidator" ControlToValidate="DropDownList1"
ClientValidationFunction="MyCustomValidation" ></asp:CustomValidator>
function MyCustomValidation(objSource, objArgs)
{
/Proceed if the control pressed is cmdSave button.
var Specialty = document.getElementById("DropDownList1").options[document.getElementById("DropDownList1").selectedIndex].text;
if (Specialty == "Select an option")
{
objArgs.IsValid = false;
}
else
{
objArgs.IsValid = true;
}
}