use textchange event on the server side and get data for that employee id and fill it. keep autopostback true for the textbox of employee id.
<asp:textbox id="txteid" runat="server" autopostback="true" ontextchange="txteid_ontextchange" xmlns:asp="#unknown"></asp:textbox>
protected void txteid_ontextchange (object sender, EventArgs e)
{
if(txteid.text!="")
{
string Eid = txteid.text
}
}