onkeyup is not working with textbox

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C#

C#4.0

ASP.NET4

function move(field,nextFieldID)
{
  if(field.value.length >= field.maxLength)
  {
    document.getElementById(nextFieldID).focus();
  }
}

=====================================================================

<asp:TextBox ID="T1" runat="server" MaxLength="3" onkeyup="move(this,'T2')">
<asp:TextBox ID="T2" runat="server" MaxLength="3" onkeyup="move(this,'T3')">
<asp:TextBox ID="T3" runat="server" MaxLength="3" onkeyup="move(this,'T1')">

=====================================================================

OnKeyUp is not working with TextBox. Even tried this too but none works for me.

T1.Attributes.Add("onkeyup", "move(this,' " + T2.ClientID + " ')"); 

Plz help me out.
Thanks in Advance.